1. Field:
[0001] The present disclosure relates generally to antennas and, in particular, to electronically-steerable
antennas. Still more particularly, the present disclosure relates to an electronically-steerable
artificial impedance antenna capable of being steered in two dimensions.
2. Background:
[0002] In various applications, having the capability to electronically steer an antenna
in two directions may be desirable. As used herein, "steering" an antenna may include
directing the primary gain lobe, or main lobe, of the radiation pattern of the antenna
in a particular direction. Electronically steering an antenna means steering the antenna
using electronic, rather than mechanical, means. Steering an antenna with respect
to two dimensions may be referred to as two-dimensional steering.
[0003] Currently, two-dimensional steering is typically provided by phased array antennas.
However, currently available phased array antennas have electronic configurations
that are more complex and/or more costly than desired. Consequently, having some other
type of antenna that can be electronically steered in two dimensions and that is low-cost
relative to a phased array antenna may be desirable.
[0004] Artificial impedance surface antennas (AISAs) may be less expensive than phased array
antennas. An artificial impedance surface antenna may be implemented by launching
a surface wave across an artificial impedance surface (AIS) having an impedance that
is spatially modulated across the artificial impedance surface according to a function
that matches the phase fronts between the surface wave on the artificial impedance
surface and the desired far-field radiation pattern. The basic principle of an artificial
impedance surface antenna operation is to use the grid momentum of the modulated artificial
impedance surface to match the wave vectors of an excited surface wave front to a
desired plane wave.
[0005] Some low-cost artificial impedance surface antennas may only be capable of being
electronically steered in one dimension. In some cases, mechanical steering may be
used to steer a one-dimensional artificial impedance surface antenna in a second dimension.
However, mechanical steering may be undesirable in certain applications.
[0006] A two-dimensional electronically-steerable artificial impedance surface antenna has
been described in prior art. However, this type of antenna is more expensive and electronically
complex than desired. For example, electronically steering this type of antenna in
two dimensions may require a complex network of voltage control for a two-dimensional
array of impedance elements. This network is used to create an arbitrary impedance
pattern that can produce beam steering in any direction.
[0007] In one illustrative example, a two-dimensional artificial impedance surface antenna
may be implemented as a grid of metallic patches on a dielectric substrate. Each metallic
path may be referred to as an impedance element. The surface wave impedance of the
artificial impedance surface may be locally controlled at each position on the artificial
impedance surface by applying a variable voltage to voltage-variable varactors connected
between each of the patches. A varactor is a semiconductor element diode that has
a capacitance dependent on the voltage applied to this diode.
[0008] The surface wave impedance of the artificial impedance surface can be tuned with
capacitive loads inserted between the patches. Each patch is electrically connected
to neighboring patches on all four sides with voltage-variable varactor capacitors.
The voltage is applied to the varactors through electrical vias connected to each
patch. An electrical via may be an electrical connection that goes through the plane
of one or more adjacent layers in an electronic circuit.
[0009] One portion of the patches may be electrically connected to the ground plane with
vias that run from the center of each patch down through the dielectric substrate.
The rest of the patches may be electrically connected to voltage sources that run
through the dielectric substrate, and through holes in the ground plane to the voltage
sources.
[0010] Computer control allows any desired impedance pattern to be applied to the artificial
impedance surface within the limits of the varactor tunability and the limitations
of the surface wave properties of the artificial impedance surface. One of the limitations
of this method is that the vias can severely reduce the operational bandwidth of the
artificial impedance surface because the vias also impart an inductance to the artificial
impedance surface that shifts the surface wave bandgap to a lower frequency. As the
varactors are tuned to higher capacitance, the artificial impedance surface inductance
is increased, which may further reduce the surface wave bandgap frequency. The net
result of the surface wave bandgap is that it does not allow the artificial impedance
surface to be used above the bandgap frequency. Further, the surface wave bandgap
also limits the range of surface wave impedance to that which the artificial impedance
surface can be tuned.
[0011] Consequently, an artificial impedance surface antenna that can be electronically
steered in two dimensions and that is less expensive and less complex than some currently
available two-dimensional artificial impedance surface antennas, such as the one described
above, may be desirable in certain applications. Therefore, it would be desirable
to have a method and apparatus that take into account at least some of the issues
discussed above, as well as other possible issues.
SUMMARY
[0012] In one illustrative embodiment, an apparatus comprises a plurality of radiating elements
and a plurality of surface wave feeds. Each radiating element in the plurality of
radiating elements comprises a number of surface wave channels in which each of the
number of surface wave channels is configured to constrain a path of a surface wave
and comprises a plurality of switch elements and a plurality of impedance elements.
A surface wave feed in the plurality of surface wave feeds is configured to couple
a surface wave channel in the number of surface wave channels of a radiating element
in the plurality of radiating elements to a transmission line configured to carry
a radio frequency signal.
[0013] In another illustrative embodiment, an antenna system comprises a plurality of radiating
elements and a plurality of surface wave feeds. Each of the plurality of radiating
elements comprises a number of surface wave channels in which each of the number of
surface wave channels is configured to constrain a path of a surface wave. Each of
the number of surface wave channels comprises a plurality of impedance elements located
on a surface of a dielectric substrate and a plurality of switch elements located
on the surface of the dielectric substrate. Each of the plurality of switch elements
has only two states. The plurality of surface wave feeds is configured to couple the
number of surface wave channels of each of the plurality of radiating elements to
a number of transmission lines.
[0014] In yet another illustrative embodiment, a method for electronically steering an antenna
system is provided. A surface wave is propagated along each of a number of surface
wave channels formed in each of a plurality of radiating elements to form a radiation
pattern. Each surface wave channel in the number of surface wave channels formed in
each radiating element in the plurality of radiating elements is coupled to a transmission
line configured to carry a radio frequency signal using a surface wave feed in a plurality
of surface wave feed associated with the plurality of radiating elements. A main lobe
of the radiation pattern is electronically steered by controlling voltages applied
to a plurality of switch elements connecting a plurality of impedance elements in
each of the number of surface wave channels.
[0015] The features and functions can be achieved independently in various embodiments of
the present disclosure or may be combined in yet other embodiments in which further
details can be seen with reference to the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The novel features believed characteristic of the illustrative embodiments are set
forth in the appended claims. The illustrative embodiments, however, as well as a
preferred mode of use, further objectives and features thereof, will best be understood
by reference to the following detailed description of an illustrative embodiment of
the present disclosure when read in conjunction with the accompanying drawings, wherein:
Figure 1 is an illustration of an antenna system in the form of a block diagram in accordance
with an illustrative embodiment;
Figure 2 is an illustration of an antenna system in accordance with an illustrative embodiment;
Figure 3 is an illustration of a side view of a portion of a tunable artificial impedance
surface antenna in accordance with an illustrative embodiment;
Figure 4 is an illustration of a different configuration for an antenna system in accordance
with an illustrative embodiment;
Figure 5 is an illustration of another configuration for an antenna system in accordance with
an illustrative embodiment;
Figure 6 is an illustration of a side view of a dielectric substrate in accordance with an
illustrative embodiment;
Figure 7 is an illustration of a dielectric substrate having embedded pockets of material
in accordance with an illustrative embodiment;
Figure 8 is an illustration of an antenna system in accordance with an illustrative embodiment;
Figure 9 is another illustration of an antenna system in accordance with an illustrative embodiment;
Figure 10 is an illustration of an antenna system with a different voltage controller in accordance
with an illustrative embodiment;
Figures 11A and 11B are an illustration of yet another configuration for an antenna system in accordance
with an illustrative embodiment;
Figure 12 is an illustration of a portion of an antenna system in accordance with an illustrative
embodiment;
Figure 13 is an illustration of an antenna system having two radio frequency assemblies in
accordance with an illustrative embodiment;
Figure 14 is an illustration of another antenna system in accordance with an illustrative embodiment;
Figure 15 is an illustration of a different configuration for an artificial impedance surface
antenna in an antenna system in the form of a block diagram in accordance with an
illustrative embodiment;
Figure 16 is an illustration of an artificial impedance surface antenna in accordance with
an illustrative embodiment;
Figure 17 is an illustration of a cross-sectional side view of an artificial impedance surface
antenna in accordance with an illustrative embodiment;
Figure 18 is an illustration of an impedance pattern for an artificial impedance surface antenna
in accordance with an illustrative embodiment;
Figure 19 is an illustration of a portion of an artificial impedance surface antenna in accordance
with an illustrative embodiment;
Figure 20 is an illustration of a cross-sectional side view of an artificial impedance surface
antenna in accordance with an illustrative embodiment;
Figure 21 is an illustration of an artificial impedance surface antenna in the form of a block
diagram in accordance with an illustrative embodiment;
Figure 22 is an illustration of a radiating element in accordance with an illustrative embodiment;
Figure 23 is an illustration of an enlarged view of a portion of a surface wave channel in
accordance with an illustrative embodiment;
Figure 24 is an illustration of a radiating element in accordance with an illustrative embodiment;
Figure 25 is an illustration of a process for electronically steering an antenna system in
the form of a flowchart in accordance with an illustrative embodiment;
Figure 26 is an illustration of a process for electronically steering an antenna system in
the form of a flowchart in accordance with an illustrative embodiment; and
Figure 27 is an illustration of a process for electronically steering an antenna system in
the form of a flowchart in accordance with an illustrative embodiment.
DETAILED DESCRIPTION
[0017] Referring now to the figures and, in particular, with reference to
Figure 1, an illustration of an antenna system in the form of a block diagram is depicted
in accordance with an illustrative embodiment. Antenna system
100 may include antenna
102, voltage controller
104, phase shifter
106, and radio frequency module
108. Antenna
102 takes the form of artificial impedance surface antenna (AISA)
110 in this illustrative example.
[0018] Antenna
102 is configured to transmit and/or receive radiation pattern
112. Radiation pattern
112 is a plot of the gain of antenna
102 as a function of direction. The gain of antenna
102 may be considered a performance parameter for antenna
102. In some cases, "gain" is considered the peak value of gain.
[0019] Antenna
102 is configured to electronically control radiation pattern
112. When antenna
102 is used for transmitting, radiation pattern
112 may be the strength of the radio waves transmitted from antenna
102 as a function of direction. Radiation pattern
112 may be referred to as a transmitting pattern when antenna
102 is used for transmitting. The gain of antenna
102, when transmitting, may describe how well antenna
102 converts electrical power into electromagnetic radiation, such as radio waves, and
transmits the electromagnetic radiation in a specified direction.
[0020] When antenna
102 is used for receiving, radiation pattern
112 may be the sensitivity of antenna
102 to radio waves as a function of direction. Radiation pattern
112 may be referred to as a receiving pattern when antenna
102 is used for receiving. The gain of antenna
102, when used for receiving, may describe how well antenna
102 converts electromagnetic radiation, such as radio waves, arriving from a specified
direction into electrical power.
[0021] The transmitting pattern and receiving pattern of antenna
102 may be identical. Consequently, the transmitting pattern and receiving pattern of
antenna
102 may be simply referred to as radiation pattern
112.
[0022] Radiation pattern
112 may include main lobe
116 and one or more side lobes. Main lobe
116 may be the lobe at the direction in which antenna
102 is being directed. When antenna
102 is used for transmitting, main lobe
116 is located at the direction in which antenna
102 transmits the strongest radio waves to form a radio frequency beam. When antenna
102 is used for transmitting, main lobe
116 may also be referred to as the primary gain lobe of radiation pattern
112. When antenna
102 is used for receiving, main lobe
116 is located at the direction in which antenna
102 is most sensitive to incoming radio waves.
[0023] In this illustrative example, antenna
102 is configured to electronically steer main lobe
116 of radiation pattern
112 in desired direction
114. Main lobe
116 of radiation pattern
112 may be electronically steered by controlling phi steering angle
118 and theta steering angle
120 at which main lobe
116 is directed. Phi steering angle
118 and theta steering angle
120 are spherical coordinates. When antenna
102 is operating in an X-Y plane, phi steering angle
118 is the angle of main lobe
116 in the X-Y plane relative to the X-axis. Further, theta steering angle
120 is the angle of main lobe
116 relative to a Z-axis that is orthogonal to the X-Y plane.
[0024] Antenna
102 may operate in the X-Y plane by having array of radiating elements
122 that lie in the X-Y plane. As used herein, an "array" of items may include one or
more items arranged in rows and/or columns. In this illustrative example, array of
radiating elements
122 may be a single radiating element or a plurality of radiating elements. In one illustrative
example, each radiating element in array of radiating elements
122 may take the form of an artificial impedance surface, surface wave waveguide structure.
[0025] Radiating element
123 may be an example of one radiating element in array of radiating elements
122. Radiating element
123 may be configured to emit radiation that contributes to radiation pattern
112.
[0026] As depicted, radiating element
123 is implemented using dielectric substrate
124. Dielectric substrate
124 may be implemented as a layer of dielectric material. A dielectric material is an
electrical insulator that can be polarized by an applied electric field.
[0027] Radiating element
123 may include one or more surface wave channels that are formed on dielectric substrate
124. For example, radiating element
123 may include surface wave channel
125. Surface wave channel
125 is configured to constrain the path of surface waves propagated along dielectric
substrate
124, and surface wave channel
125 in particular.
[0028] In one illustrative example, array of radiating elements
122 may be positioned substantially parallel to the X-axis and arranged and spaced along
the Y-axis. Further, when more than one surface wave channel is formed on a dielectric
substrate, these surface wave channels may be formed substantially parallel to the
X-axis and arranged and spaced along the Y-axis.
[0029] In this illustrative example, impedance elements and tunable elements located on
a dielectric substrate may be used to form each surface wave channel of a radiating
element in array of radiating elements
122. For example, surface wave channel
125 may be comprised of plurality of impedance elements
126 and plurality of tunable elements
128 located on the surface of dielectric substrate
124. Together, plurality of impedance elements
126, plurality of tunable elements
128, and dielectric substrate
124 form an artificial impedance surface from which radiation is generated.
[0030] An impedance element in plurality of impedance elements
126 may be implemented in a number of different ways. In one illustrative example, an
impedance element may be implemented as a resonating element. In one illustrative
example, an impedance element may be implemented as an element comprised of a conductive
material. The conductive material may be, for example, without limitation, a metallic
material. Depending on the implementation, an impedance element may be implemented
as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic
film, a deposit of a metallic substrate, or some other type of conductive element.
In some cases, an impedance element may be implemented as a resonant structure such
as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR),
a structure comprised of one or more metamaterials, or some other type of structure
or element.
[0031] As used herein, a metamaterial may be an artificial material engineered to have properties
that may not be found in nature. A metamaterial may be an assembly of multiple individual
elements formed from conventional microscopic materials. These conventional materials
may include, for example, without limitation, metal, a metal alloy, a plastic material,
and other types of materials. However, these conventional materials may be arranged
in repeating patterns. The properties of a metamaterial may be based, not on the composition
of the metamaterial, but on the exactingly-designed structure of the metamaterial.
In particular, the precise shape, geometry, size, orientation, arrangement, or combination
thereof may be exactly designed to produce a metamaterial with specific properties
that may not be found or readily found in nature.
[0032] Each one of plurality of tunable elements
128 may be an element that can be controlled, or tuned, to change an angle of the one
or more surface waves being propagated along radiating element
123. In this illustrative example, each of plurality of tunable elements
128 may be an element having a capacitance that can be varied based on the voltage applied
to the tunable element.
[0033] In one illustrative example, plurality of impedance elements
126 takes the form of plurality of metallic strips
132 and plurality of tunable elements
128 takes the form of plurality of varactors
134. Each of plurality of varactors
134 may be a semiconductor element diode that has a capacitance dependent on the voltage
applied to the semiconductor element diode.
[0034] In one illustrative example, plurality of metallic strips
132 may be arranged in a row that extends along the X-axis. For example, plurality of
metallic strips
132 may be periodically distributed on dielectric substrate
124 along the X-axis. Plurality of varactors
134 may be electrically connected to plurality of metallic strips
132 on the surface of dielectric substrate
124. In particular, at least one varactor in plurality of varactors
134 may be positioned between each adjacent pair of metallic strips in plurality of metallic
strips
132. Further, plurality of varactors
134 may be aligned such that all of the varactor connections on each metallic strip have
the same polarity.
[0035] Dielectric substrate
124, plurality of impedance elements
126, and plurality of tunable elements
128 may be configured with respect to selected design configuration
136 for surface wave channel
125, and radiating element
123 in particular. Depending on the implementation, each radiating element in array of
radiating elements
122 may have a same or different selected design configuration.
[0036] As depicted, selected design configuration
136 may include a number of design parameters such as, but not limited to, impedance
element width
138, impedance element spacing
140, tunable element spacing
142, and substrate thickness
144. Impedance element width
138 may be the width of an impedance element in plurality of impedance elements
126. Impedance element width
138 may be selected to be the same or different for each of plurality of impedance elements
126, depending on the implementation.
[0037] Impedance element spacing
140 may be the spacing of plurality of impedance elements
126 with respect to the X-axis. Tunable element spacing
142 may be the spacing of plurality of tunable elements
128 with respect to the X-axis. Further, substrate thickness
144 may be the thickness of dielectric substrate
124 on which a particular waveguide is implemented.
[0038] The values for the different parameters in selected design configuration
136 may be selected based on, for example, without limitation, the radiation frequency
at which antenna
102 is configured to operate. Other considerations include, for example, the desired
impedance modulations for antenna
102.
[0039] Voltages may be applied to plurality of tunable elements
128 by applying voltages to plurality of impedance elements
126 because plurality of impedance elements
126 may be electrically connected to plurality of tunable elements
128. In particular, the voltages applied to plurality of impedance elements
126, and thereby plurality of tunable elements
128, may change the capacitance of plurality of tunable elements
128. Changing the capacitance of plurality of tunable elements
128 may, in turn, change the surface impedance of antenna
102. Changing the surface impedance of antenna
102 changes radiation pattern
112 produced.
[0040] In other words, by controlling the voltages applied to plurality of impedance elements
126, the capacitances of plurality of tunable elements
128 may be varied. Varying the capacitances of plurality of tunable elements
128 may vary, or modulate, the capacitive coupling and impedance between plurality of
impedance elements
126. Varying, or modulating, the capacitive coupling and impedance between plurality
of impedance elements
126 may change theta steering angle
120.
[0041] The voltages may be applied to plurality of impedance elements
126 using voltage controller
104. Voltage controller
104 may include number of voltage sources
146, number of grounds
148, number of voltage lines
150, and/or some other type of component. In some cases, voltage controller
104 may be referred to as a voltage control network. As used herein, a "number of" items
may include one or more items. For example, number of voltage sources
146 may include one or more voltage sources; number of grounds
148 may include one or more grounds; and number of voltage lines
150 may include one or more voltage lines.
[0042] A voltage source in number of voltage sources
146 may take the form of, for example, without limitation, a digital to analog converter
(DAC), a variable voltage source, or some other type of voltage source. Number of
grounds
148 may be used to ground at least a portion of plurality of impedance elements
126. Number of voltage lines
150 may be used to transmit voltage from number of voltage sources
146 and/or number of grounds
148 to plurality of impedance elements
126. In some cases, each of number of voltage lines
150 may be referred to as a via. In one illustrative example, number of voltage lines
150 may take the form of a number of metallic vias.
[0043] In one illustrative example, each of plurality of impedance elements
126 may receive voltage from one of number of voltage sources
146. In another illustrative example, a portion of plurality of impedance elements
126 may receive voltage from number of voltage sources
146 through a corresponding portion of number of voltage lines
150, while another portion of plurality of impedance elements
126 may be electrically connected to number of grounds
148 through a corresponding portion of number of voltage lines
150.
[0044] In some cases, controller
151 may be used to control number of voltage sources
146. Controller
151 may be considered part of or separate from antenna system
100, depending on the implementation. Controller
151 may be implemented using a microprocessor, an integrated circuit, a computer, a central
processing unit, a plurality of computers in communication with each other, or some
other type of computer or processor.
[0045] Surface waves
152 propagated along array of radiating elements
122 may be coupled to number of transmission lines
156 by plurality of surface wave feeds
130 located on dielectric substrate
124. A surface wave feed in plurality of surface wave feeds
130 may be any device that is capable of converting a surface wave into a radio frequency
signal and/or a radio frequency signal into a surface wave. In one illustrative example,
a surface wave feed in plurality of surface wave feeds
130 is located at the end of each waveguide in array of radiating elements
122 on dielectric substrate
124.
[0046] For example, when antenna
102 is in a receiving mode, the one or more surface waves propagating along radiating
element
123 may be received at a corresponding surface wave feed in plurality of surface wave
feeds
130 and converted into a corresponding radio frequency signal
154. Radio frequency signal
154 may be sent to radio frequency module
108 over one or more of number of transmission lines
156. Radio frequency module
108 may then function as a receiver and process radio frequency signal
154 accordingly.
[0047] Depending on the implementation, radio frequency module
108 may function as a transmitter, a receiver, or a combination of the two. In some illustrative
examples, radio frequency module
108 may be referred to as transmit/receive module
158. In some cases, when configured for transmitting, radio frequency module
108 may be referred to as a radio frequency source.
[0048] In some cases, radio frequency signal
154 may pass through phase shifter
106 prior to being sent to radio frequency module
108. Phase shifter
106 may include any number of phase shifters, power dividers, transmission lines, and/or
other components configured to shift the phase of radio frequency signal
154. In some cases, phase shifter
106 may be referred to as a phase-shifting network.
[0049] When antenna
102 is in a transmitting mode, radio frequency signal
154 may be sent from radio frequency module
108 to antenna
102 over number of transmission lines
156. In particular, radio frequency signal
154 may be received at one of plurality of surface wave feeds
130 and converted into one or more surface waves that are then propagated along a corresponding
waveguide in array of radiating elements
122.
[0050] In this illustrative example, the relative phase difference between plurality of
surface wave feeds
130 may be changed to change phi steering angle
118 of radiation pattern
112 that is transmitted or received. Thus, by controlling the relative phase difference
between plurality of surface wave feeds
130 and controlling the voltages applied to the tunable elements of each waveguide in
array of radiating elements
122, phi steering angle
118 and theta steering angle
120, respectively, may be controlled. In other words, antenna
102 may be electronically steered in two dimensions.
[0051] Depending on the implementation, radiating element
123 may be configured to emit linearly polarized radiation or circularly polarized radiation.
When configured to emit linearly polarized radiation, the plurality of metallic strips
used for each surface wave channel on radiating element
123 may be angled in the same direction relative to the X-axis along which the plurality
of metallic strips are distributed. Typically, only a single surface wave channel
is needed for each radiating element
123.
[0052] However, when radiating element
123 is configured for producing circularly polarized radiation, surface wave channel
125 may be a first surface wave channel and second surface wave channel
145 may be also present in radiating element
123. Surface wave channel
125 and second surface wave channel
145 may be about 90 degrees out of phase from each other. The interaction between the
radiation from these two coupled surface wave channels makes it possible to create
circularly polarized radiation.
[0053] Plurality of impedance elements
126 that form surface wave channel
125 may be a first plurality of impedance elements that radiate with a polarization at
an angle to the polarization of the surface wave electric field. A second plurality
of impedance elements that form second surface wave channel
145 may radiate with a polarization at an angle offset about 90 degrees as compared to
surface wave channel
125.
[0054] For example, each impedance element in the first plurality of impedance elements
of surface wave channel
125 may have a tensor impedance with a principal angle that is angled at a first angle
relative to an X-axis of radiating element
123. Further, each impedance element in the second plurality of impedance elements of
second surface wave channel
145 may have a tensor impedance that is angled at a second angle relative to the X-axis
of the corresponding radiating element. The difference between the first angle and
the second angle may be about 90 degrees.
[0055] The capacitance between the first plurality of impedance elements may be controlled
using plurality of tunable elements
128, which may be a first plurality of tunable elements. The capacitance between the
second plurality of impedance elements may be controlled using a second plurality
of tunable elements.
[0056] As a more specific example, plurality of metallic strips
132 on surface wave channel
125 may be angled at about positive 45 degrees with respect to the X-axis along which
plurality of metallic strips
132 is distributed. However, the plurality of metallic strips used for second surface
wave channel
145 may be angled at about negative 45 degrees with respect to the X-axis along which
the plurality of metallic strips is distributed. This variation in tilt angle produces
radiation of different linear polarizations, that when combined with a 90 degree phase
shift, may produce circularly polarized radiation.
[0057] The illustration of antenna system
100 in
Figure 1 is not meant to imply physical or architectural limitations to the manner in which
an illustrative embodiment may be implemented. Other components in addition to or
in place of the ones illustrated may be used. Some components may be optional. Also,
the blocks are presented to illustrate some functional components. One or more of
these blocks may be combined, divided, or combined and divided into different blocks
when implemented in an illustrative embodiment.
[0058] For example, in other illustrative examples, phase shifter
106 may not be included in antenna system
100. Instead, number of transmission lines
156 may be used to couple plurality of surface wave feeds
130 to a number of power dividers and/or other types of components, and these different
components to radio frequency module
108. In some examples, number of transmission lines
156 may directly couple plurality of surface wave feeds
130 to radio frequency module
108.
[0059] In some illustrative examples, a tunable element in plurality of tunable elements
128 may be implemented as a pocket of variable material embedded in dielectric substrate
124. As used herein, a "variable material" may be any material having a permittivity
that may be varied. The permittivity of the variable material may be varied to change,
for example, the capacitance between two impedance elements between which the variable
material is located. The variable material may be a voltage-variable material or any
electrically variable material, such as, for example, without limitation, a liquid
crystal material or barium strontium titanate (BST).
[0060] In other illustrative examples, a tunable element in plurality of tunable elements
128 may be part of a corresponding impedance element in plurality of impedance elements
126. For example, a resonant structure having a tunable element may be used. The resonant
structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled
resonator, or some other type of resonant structure.
[0061] With reference now to
Figure 2, an illustration of an antenna system is depicted in accordance with an illustrative
embodiment. Antenna system
200 may be an example of one implementation for antenna system
100 in
Figure 1. As depicted, antenna system
200 includes tunable artificial impedance surface antenna (AISA)
201, which may be an example of one implementation for artificial impedance surface antenna
110 in
Figure 1. Further, antenna system
200 may also include voltage controller
202 and phase shifter
203. Voltage controller
202 and phase shifter
203 may be examples of implementations for voltage controller
104 and phase shifter
106, respectively, in
Figure 1.
[0062] In this illustrative example, tunable artificial impedance surface antenna
201 is a relatively low cost antenna capable of being electronically steered in both
theta, θ, and phi, φ, directions. When tunable artificial impedance surface antenna
201 is operating in the X-Y plane, the theta direction may be a direction perpendicular
to the Z axis that is perpendicular to the X-Y plane, while the phi direction may
be a direction parallel to the X-Y plane.
[0063] As depicted, tunable artificial impedance surface antenna
201 includes dielectric substrate
206, metallic strips
207, varactors
209, and radio frequency (RF) surface wave feeds
208. Metallic strips
207 may be a periodic array of metallic strips
207 that are located on one surface of dielectric substrate
206. Varactors
209 may be located between metallic strips
207. Dielectric substrate
206 may or may not have a ground plane (not shown in this view) on a surface of dielectric
substrate
206 opposite to the surface on which metallic strips
207 are located.
[0064] Steering of the main lobe of tunable artificial impedance surface antenna
201 in the theta direction is controlled by varying, or modulating, the surface wave
impedance of tunable artificial impedance surface antenna
201. For example, the impedance of tunable artificial impedance surface antenna
201 may be varied, or modulated, by controlling the voltages applied to metallic strips
207 located on the surface of dielectric substrate
206. With varactors
209 present between metallic strips
207, the voltage applied to varactors
209 may be controlled using metallic strips
207. Each of varactors
209 is a type of diode that has a capacitance that varies as a function of the voltage
applied across the terminals of the diode.
[0065] The voltages applied to metallic strips
207 may change the capacitance of varactors
209 between metallic strips
207, which may, in turn, change the impedance of tunable artificial impedance surface
antenna
201. In other words, by controlling the voltages applied to metallic strips
207, the capacitances of varactors
209 may be varied. Varying the capacitances of varactors
209 may vary or modulate the capacitive coupling and impedance between metallic strips
207 to steer the beam produced by antenna system
200 in the theta direction.
[0066] In this illustrative example, radio frequency surface wave feeds
208 may be a two-dimensional array of radio frequency surface wave feeds. Steering of
the main lobe of tunable artificial impedance surface antenna
201 in the phi direction is controlled by changing the relative phase difference between
radio frequency surface wave feeds
208.
[0067] Voltage controller
202 is used to apply direct current (DC) voltages to metallic strips
207 on the structure of tunable artificial impedance surface antenna
201. Voltage controller
202 may be controlled based on commands received through control bus
205. In this manner, control bus
205 provides control for voltage controller
202. Further, control bus
204 may provide control for phase shifter
203. Each of control bus
204 and control bus
205 may be a bus from a microprocessor, a central processing unit (CPU), one or more
computers, or some other type of computer or processor.
[0068] In this illustrative example, the polarities of varactors
209 may be aligned such that all varactor connections to any one of metallic strips
207 may be connected with the same polarity. One terminal on a varactor may be referred
to as an anode, and the other terminal may be referred to as a cathode. Thus, some
of metallic strips
207 are only connected to anodes of varactors
209, while other of metallic strips
207 are only connected to cathodes of varactors
209. Further, as depicted, adjacent metallic strips
207 may alternate with respect to which ones are connected to the anodes of varactors
209 and which ones are connected to the cathodes of varactors
209.
[0069] The spacing of metallic strips
207 in one dimension of tunable artificial impedance surface antenna
201, which may be in an X direction, may be a fraction of the radio frequency surface
wave wavelength of the radio frequency waves that propagate across tunable artificial
impedance surface antenna
201 from radio frequency surface wave feeds
208. In one illustrative example, the spacing of metallic strips
207 may be at most 2/5 of the radio frequency surface wave wavelength of the radio frequency
waves. In another illustrative example, the fraction may be only about 2/10 of the
radio frequency surface wave wavelength of the radio frequency waves. Depending on
the implementation, the spacing between varactors
209 connected to metallic strips
207 in a second dimension of tunable artificial impedance surface antenna
201, which may be in a Y direction, may be about the same as the spacing between metallic
strips
207.
[0070] Radio frequency surface wave feeds
208 may form a phased array corporate feed structure, or may take the form of conformal
surface wave feeds, which are integrated into tunable artificial impedance surface
antenna
201. The surface wave feeds may be integrated into tunable artificial impedance surface
antenna
201, for example, using microstrips. The spacing between radio frequency surface wave
feeds
208 in the Y direction may be based on selected rules that indicate that the spacing
be no farther apart than the free-space wavelength for the highest frequency signal
to be transmitted or received.
[0071] In this illustrative example, the thickness of dielectric substrate
206 may be determined by the permittivity of dielectric substrate
206 and the frequency of radiation to be transmitted or received. The higher the permittivity,
the thinner dielectric substrate
206 may be.
[0072] The capacitance values of varactors
209 may be determined by the range needed for the desired impedance modulations for tunable
artificial impedance surface antenna
201 in order to obtain the various angles of radiation. Further, the particular substrate
used for dielectric substrate
206 may be selected based on the operating frequency, or radio frequency, of tunable
artificial impedance surface antenna
201.
[0073] For example, when tunable artificial impedance surface antenna
201 is operating at about 20 gigahertz, dielectric substrate
206 may be implemented using, without limitation, a substrate, available from Rogers
Corporation, having a thickness of about 50 millimeters (mm). In this example, dielectric
substrate
206 may have a relative permittivity equal to about 12.2. Metallic strips
207 may be spaced about two millimeters to about three millimeters apart on dielectric
substrate
206. Further, radio frequency surface wave feeds
208 may be spaced about 2.5 centimeters apart and varactors
209 may be spaced about two millimeters to about three millimeters apart in this example.
Varactors
209 may vary in capacitance from about 0.2 picofarads (pF) to about 2.0 picofarads. Of
course, other specifications may be used for tunable artificial impedance surface
antenna
201 for different radiation frequencies.
[0074] To transmit or receive a radio frequency signal using tunable artificial impedance
surface antenna
201, transmit/receive module
210 is connected to phase shifter
203. Phase shifter
203 may be a one-dimensional phase shifter in this illustrative example. Phase shifter
203 may be implemented using any type of currently available phase shifter, including
those used in phased array antennas.
[0075] In this illustrative example, phase shifter
203 includes radio frequency transmission lines
211 connected to transmit/receive module
210, power dividers
212, and phase shifters
213. Phase shifters
213 are controlled by voltage control lines
216 connected to digital to analog converter (DAC)
214. Digital to analog converter
214 receives digital control signals from control bus
204 to control the steering in the phi direction.
[0076] The main lobe of tunable artificial impedance surface antenna
201 may be steered in the phi direction by using phase shifter
203 to impose a phase shift between each of radio frequency surface wave feeds
208. If radio frequency surface wave feeds
208 are spaced uniformly, then the phase shift between adjacent radio frequency surface
wave feeds
208 may be substantially constant. The relationship between the phi (φ) steering angle
and the phase shift may be calculated using standard phased array methods, according
to the following equation:
where λ is the radiation wavelength,
d is the spacing between radio frequency surface wave feeds
208, and Δψ is the phase shift between these surface wave feeds. In some cases, these
surface wave feeds may also be spaced non-uniformly, and the phase shifts adjusted
accordingly.
[0077] As described earlier, the main lobe of tunable artificial impedance surface antenna
201 may be steered in the theta (θ) direction by applying voltages to varactors
209 such that tunable artificial impedance surface antenna
201 has surface wave impedance Z
sw, which is modulated or varied periodically with the distance (
x) away from radio frequency surface wave feeds
208, according to the following equation:
where
X and
M are the mean impedance and the amplitude, respectively, of the modulation of tunable
artificial impedance surface antenna
201, and
p is the modulation period. The variation of the surface wave impedance, Z
SW, may be modulated sinusoidally. The theta steering angle, θ, is related to the impedance
modulation by the following equation:
where λ is the wavelength of the radiation, and
is the mean surface wave index.
[0078] The beam is steered in the theta direction by tuning the voltages applied to varactors
209 such that
X,
M, and
p result in the desired theta steering angle, θ. The dependence of the surface wave
impedance on the varactor capacitance is calculated using transcendental equations
resulting from the transverse resonance method or by using full-wave numerical simulations.
[0079] Voltages may be applied to varactors
209 by grounding alternate metallic strips
207 to ground
220 via voltage control lines
218 and applying tunable voltages via voltage control lines
219 to the rest of metallic strips
207. The voltage applied to each of voltage control lines
219 may be a function of the desired theta steering angle and may be different for each
of voltage control lines
219. The voltages may be applied from digital-to-analog converter (DAC)
217 that receives digital controls from control bus
205 from a controller for steering in the theta direction. The controller may be a microprocessor,
central processing unit (CPU) or any computer, processor or controller.
[0080] One benefit of grounding half of metallic strips
207 is that only half as many voltage control lines
219 are required as there are metallic strips
207. However, in some cases, the spatial resolution of the voltage control and hence,
the impedance modulation, may be limited to twice the spacing between metallic strips
207.
[0081] With reference now to
Figure 3, an illustration of a side view of a portion of tunable artificial impedance surface
antenna
201 from
Figure 2 is depicted in accordance with an illustrative embodiment. In this illustrative example,
dielectric substrate
206 has ground plane
300.
[0082] With reference now to
Figure 4, an illustration of a different configuration for an antenna system is depicted in
accordance with an illustrative embodiment. Antenna system
400 may be an example of one implementation for antenna system
100 in
Figure 1. Antenna system
400 includes tunable artificial impedance surface antenna (AISA)
401, which may be an example of one implementation for artificial impedance surface antenna
110 in
Figure 1.
[0083] Antenna system
400 and tunable artificial impedance surface antenna
401 may be implemented in a manner similar to antenna system
200 and tunable artificial impedance surface antenna
201, respectively, from
Figure 2. As depicted, antenna system
400 includes tunable artificial impedance surface antenna
401, voltage controller
402, and phase shifter
403. Tunable artificial impedance surface antenna
401 includes dielectric substrate
406, metallic strips
407, varactors
409, and radio frequency surface wave feeds
408. Further, antenna system
400 may include transmit/receive module
410.
[0084] However, in this illustrative example, voltage controller
402 may be implemented in a manner different from the manner in which voltage controller
202 is implemented in
Figure 2. In
Figure 4, voltage controller
402 may include voltage lines
411 that allow voltage to be applied from digital to analog converter
412 to each of metallic strips
407. Alternating metallic strips
407 are not grounded as in
Figure 2. Digital to analog converter
412 may receive digital controls from control bus
205 in
Figure 2 from, for example, controller
414, for steering in the theta direction. Controller
414 may be implemented using a microprocessor, a central processing unit, or some other
type of computer or processor. Steering in the phi direction may be performed using
phase shifter
403 in a manner similar to the manner in which phase shifter
203 is used in
Figure 2.
[0085] With voltage lines
411 applying voltage to all of metallic strips
407, twice as many control voltages are required compared to antenna system
200 in
Figure 2. However, the spatial resolution of the impedance modulation of tunable artificial
impedance surface antenna
401 is doubled. In this illustrative example, the voltage applied to each of voltage
lines
411 is a function of the desired theta steering angle, and may be different for each
of voltage lines
411.
[0086] With reference now to
Figure 5, an illustration of another configuration for an antenna system is depicted in accordance
with an illustrative embodiment. Antenna system
500 may be an example of one implementation for antenna system
100 in
Figure 1. Antenna system
500 includes tunable artificial impedance surface antenna (AISA)
501, which may be an example of one implementation for artificial impedance surface antenna
110 in
Figure 1.
[0087] Antenna system
500 and tunable artificial impedance surface antenna
501 may be implemented in a manner similar to antenna system
200 and tunable artificial impedance surface antenna
201, respectively, from
Figure 2. Further, antenna system
500 and tunable artificial impedance surface antenna
501 may be implemented in a manner similar to antenna system
400 and tunable artificial impedance surface antenna
401, respectively, from
Figure 4.
[0088] As depicted, antenna system
500 includes tunable artificial impedance surface antenna
501, voltage controller
502, and phase shifter
503. Tunable artificial impedance surface antenna
501 includes dielectric substrate
506, metallic strips
507, varactors
509, and radio frequency surface wave feeds
508. Further, antenna system
500 may include transmit/receive module
510.
[0089] However, in this illustrative example, voltage controller
502 may be implemented in a manner different from the manner in which voltage controller
202 is implemented in
Figure 2 and in a manner different from the manner in which voltage controller
402 is implemented in
Figure 4. In
Figure 5, the digital to analog converters of
Figure 2 and
Figure 4 have been replaced by variable voltage source
512.
[0090] As the voltage of variable voltage source
512 is varied, the radiation angle of the beam produced by tunable artificial impedance
surface antenna
501 varies between a minimum theta steering angle and a maximum theta steering angle.
This range for the theta steering angle may be determined by the details of the design
configuration of tunable artificial impedance surface antenna
501.
[0091] The voltage is applied to metallic strips
507 through voltage control lines
514 and voltage control lines
516. Voltage control lines
516 may provide a ground for metallic strips
507, while voltage control lines
514 may provide metallic strips
507 with a variable voltage. Across the X dimension, metallic strips
507 are alternately connected to voltage control lines
514 or voltage control lines
516. In other words, alternating metallic strips
507 are grounded.
[0092] Metallic strips
507 may have centers that are equally spaced in the X dimension, with the widths of metallic
strips
507 periodically varying with a period (
p)
518. The number of metallic strips
507 in period
518 may be any number. For example, metallic strips
507 may be between 10 and 20 metallic strips per period
518. The width variation per period
518 may be configured to produce surface wave impedance with a periodic modulation in
the X-direction with period
518, such as, for example, the sinusoidal variation of equation (3) described above.
[0093] The surface wave impedance at each point on tunable artificial impedance surface
antenna
501 is determined by the width of each of metallic strips
507 and the voltage applied to varactors
509. The capacitance of varactors
509 may vary with the varying applied voltage. When the voltage is about 0 volts, the
capacitance of a varactor may be at a maximum value of
Cmax. The capacitance decreases as the voltage is increased until the capacitance reaches
a minimum value of
Cmin. As the capacitance is varied, the impedance modulation parameters,
X and
M, as described in equation 2 above, may also vary from minimum values of X
min and M
min, respectively, to maximum values of X
max and M
max, respectively.
[0094] Further, the mean surface wave index of equation 4 described above varies from
to
Further, as described in equation 3 above, the range that the radiation angle of
tunable artificial impedance surface antenna
501 may be scanned may vary from a minimum of
to a maximum of
with variation of a single control voltage.
[0095] With reference now to
Figure 6, an illustration of a side view of a dielectric substrate is depicted in accordance
with an illustrative embodiment. In this illustrative example, dielectric substrate
601 may be used to implement dielectric substrate
206 from
Figure 2, dielectric substrate
406 from
Figure 4, and/or dielectric substrate
506 from
Figure 5. Dielectric substrate
601 may have an electrical permittivity that is varied with the application of an electric
field.
[0096] Metallic strips
602 are shown located on one surface of dielectric substrate
601. As depicted, no varactors are used in this illustrative example. When a voltage
is applied to metallic strips
602, an electric field is produced between adjacent metallic strips
602 and also between metallic strips
602 and ground plane
603. The electric field changes the permittivity of dielectric substrate
601, which results in a change in the capacitance between adjacent metallic strips
602. The capacitance between adjacent metallic strips
602 determines the surface wave impedance of the tunable artificial impedance surface
antenna that uses dielectric substrate
601.
[0097] With reference now to
Figure 7, an illustration of dielectric substrate
601 from
Figure 6 having embedded pockets of material is depicted in accordance with an illustrative
embodiment. In this illustrative example, dielectric substrate
601 may take the form of inert substrate
700. A voltage differential may be applied to adjacent metallic strips
602, which may create an electric field between metallic strips
602 and produce a permittivity change in pockets of variable material
702 located between metallic strips
602.
[0098] Pockets of variable material
702 may be an example of one manner in which plurality of tunable elements
128 in
Figure 1 may be implemented. The variable material in pockets of variable material
702 may be any electrically variable material, such as, for example, without limitation,
a liquid crystal material or barium strontium titanate (BST). In particular, variable
material
702 is embedded in pockets within dielectric substrate
601 between metallic strips
602.
[0099] With reference now to
Figure 8, an illustration of an antenna system is depicted in accordance with an illustrative
embodiment. In this illustrative example, antenna system
800 may be an example of one implementation for antenna system
100 in
Figure 1. Antenna system
800 includes antenna
802, voltage controller
803, phase shifter
804, and radio frequency module
806. Antenna
802, voltage controller
803, phase shifter
804, and radio frequency module
806 may be examples of implementations for antenna
102, voltage controller
104, phase shifter
106, and radio frequency module
108, respectively, in
Figure 1.
[0100] Antenna
802 is supplied voltage by voltage controller
803. Voltage controller
803 includes digital to analog converter (DAC)
808 and voltage lines
811. Digital to analog converter
808 may be an example of one implementation for a voltage source in number of voltage
sources
146 in
Figure 1. Voltage lines
811 may be an example of one implementation for number of voltage lines
150 in
Figure 1.
[0101] Voltage may be applied to antenna
802 from digital to analog converter
808 through voltage lines
811. Controller
810 may be used to control the voltage signals sent from digital to analog converter
808 to antenna
802. Controller
810 may be an example of one implementation for controller
151 in
Figure 1. In this illustrative example, controller
810 may be considered part of antenna system
800.
[0102] As depicted, antenna
802 may include radiating structure
812 formed by array of radiating elements
813. Array of radiating elements
813 may be an example of one implementation for array of radiating elements
122 in
Figure 1. In this illustrative example, each radiating element in array of radiating elements
813 may be implemented as an artificial impedance surface, surface wave waveguide.
[0103] Array of radiating elements
813 may include radiating elements
814, 815, 816, 818, 820, 822, 824, and
826. Each of these radiating elements may be implemented using a dielectric substrate.
Further, each of these dielectric substrates may have a plurality of metallic strips,
a plurality of varactors, and a surface wave feed located on the surface of the dielectric
substrate that forms a surface wave channel for the corresponding radiating element.
[0104] As one illustrative example, radiating element
814 may be formed by dielectric substrate
827. Plurality of metallic strips
828 and plurality of varactors
830 may be located on the surface of dielectric substrate
827 to form surface wave channel
831. Further, surface wave feed
832 may be located on the surface of dielectric substrate
827. Plurality of metallic strips
828 and plurality of varactors
830 may be examples of implementations for plurality of metallic strips
132 and plurality of varactors
134, respectively, in
Figure 1.
[0105] In the transmitting mode, surface wave feed
832 feeds a surface wave into surface wave channel
831 of radiating element
814. Surface wave channel
831 confines the surface wave to propagate linearly along a confined path across plurality
of metallic strips
828. In particular, surface wave channel
831 creates a region of high surface wave index surrounded by a region of lower surface
wave index to confine the surface wave to the set path. The surface wave index is
the ratio between the speed of light and the propagation speed of the surface wave.
[0106] The regions of high surface wave index are created by plurality of metallic strips
828 and plurality of varactors
830, while the regions of low surface wave index are created by the bare surface of dielectric
substrate
827. The widths of the regions of high surface wave index may be 50 percent to about
100 percent times the length of the surface wave wavelength. The surface wave wavelength
is as follows:
where λ
sw is the surface wave wavelength,
f is the frequency of the surface wave, c is the speed of light, and
nsw is the surface wave index.
[0107] Each of plurality of metallic strips
828 located on dielectric substrate
827 may have the same width. Further, these metallic strips may be equally spaced along
dielectric substrate
827. Additionally, plurality of varactors
830 may also be equally spaced along dielectric substrate
827. In other words, plurality of metallic strips
828 and plurality of varactors
830 may be periodically distributed on dielectric substrate
827. Further, plurality of varactors
830 may be aligned such that all of the varactors connections of plurality of metallic
strips
828 have the same polarity.
[0108] The thickness of dielectric substrate
827 may be determined by its permittivity and the frequency of radiation to be transmitted
or received. The higher the permittivity, the thinner dielectric substrate
827 may be.
[0109] The capacitance values of plurality of varactors
830 may be determined by the range needed for the desired impedance modulations for the
various angles of radiation. The main lobe of the radiation pattern produced by antenna
802 may be electronically steered in the theta direction by applying voltages to the
various varactors in array of radiating elements
813. Voltage may be applied to these varactors such that antenna
802 has a surface wave impedance that varies sinusoidally with a distance, x, away from
the surface wave feeds on the different dielectric substrates.
[0110] Voltage from digital to analog converter
808 may be applied to the metallic strips on array of radiating elements
813 through voltage lines
811. In this illustrative example, surface waves propagated across array of radiating
elements
813 may be coupled to phase shifter
804 by the surface wave feeds on array of radiating elements
813. Phase shifter
804 includes plurality of phase-shifting devices
834.
[0111] The main lobe of antenna
802 may be electronically steered in the phi direction by imposing a phase shift between
each of the surface wave feeds on array of radiating elements
813. If the surface wave feeds are uniformly spaced, the phase shift between adjacent
surface wave feeds may be substantially constant. The relation between the phi steering
angle and this phase shift may be calculated as follows:
[0112] In other illustrative examples, a radio frequency module, a phase shifter, and a
plurality of surface wave feeds may be present on the opposite side of antenna
802 relative to radio frequency module
806. This configuration may be used in order to facilitate steering in the negative theta
direction.
[0113] With reference now to
Figure 9, another illustration of an antenna system is depicted in accordance with an illustrative
embodiment. In this illustrative example, antenna system
900 may be an example of one implementation for antenna system
100 in
Figure 1. Antenna system
900 includes antenna
902, voltage controller
903, phase shifter
904, and radio frequency module
906.
[0114] Voltage controller
903 is configured to supply voltage to antenna
902. Voltage controller
903 includes variable voltage source
908. Voltage lines
911 apply voltage to antenna
902, while voltage lines
913 provide ground for antenna
902.
[0115] Antenna
902 may include array of radiating elements
915 that may include radiating elements
912, 914, 916, 918, 920, 922, 924, and
926. Each of these radiating elements may be implemented using a dielectric substrate.
A surface wave channel may be formed on each radiating element by a plurality of metallic
strips, a plurality of varactors, and the dielectric substrate.
[0116] For example, radiating element
912 may be formed using dielectric substrate
927. First plurality of metallic strips
928, second plurality of metallic strips
930, and plurality of varactors
932 located on the surface of dielectric substrate
927 may form surface wave channel
931. Surface wave feed
933 is also located on the surface of dielectric substrate
927 and couples a surface wave propagated along surface wave channel
931 to phase shifter
904.
[0117] Each of first plurality of metallic strips
928 located on array of radiating elements
915 may have the same width. Further, each of second plurality of metallic strips
930 located on array of radiating elements
915 may have the same width. The width of the metallic strips in both first plurality
of metallic strips
928 and second plurality of metallic strips
930 varies periodically along dielectric substrate
927 with period,
p,
934. This period may be determined by the size of the metallic strips, the radiation
frequency, the theta steering angle, and the properties and thickness of dielectric
substrate
927.
[0118] Although only two widths for the metallic strips are shown within one period, any
number of metallic strips may be included within a period. Further, any number of
different widths may be included within a period.
[0119] Voltage from variable voltage source
908 may be applied to first plurality of metallic strips
928 through voltage lines
911. Second plurality of metallic strips
930 may be grounded through voltage lines
913.
[0120] In this illustrative example, surface waves propagated over array of radiating elements
915 may be transmitted to phase shifter
904 as radio frequency signals by the surface wave feeds on array of radiating elements
915. As depicted, phase shifter
904 includes plurality of phase-shifting devices
936.
[0121] Transmission lines
938 couple the surface wave feeds to plurality of phase-shifting devices
936 and couple plurality of phase-shifting devices
936 to radio frequency module
906. Radio frequency module
906 may be configured to function as a transmitter, a receiver, or a combination of the
two.
[0122] Turning now to
Figure 10, an illustration of antenna system
900 from
Figure 9 with a different voltage controller is depicted in accordance with an illustrative
embodiment. In this illustrative example, voltage controller
903 from
Figure 9 has been replaced with voltage controller
1000. Voltage controller
1000 includes ground
1002, digital to analog converter
1004, voltage lines
1006, and voltage lines
1008.
[0123] Voltage lines
1006 allow second plurality of metallic strips
930 to be grounded to ground
1002. Voltage lines
1008 supply voltage from digital to analog converter
1004 to first plurality of metallic strips
928. Controller
1010 is used to control digital to analog converter
1004. In this illustrative example, different voltages are sent to each radiating element
in array of radiating elements
915.
[0124] Further, as depicted, phase shifter
904 is not included in this configuration for antenna system
900. Transmission lines
1012 directly couple radio frequency module
906 to the surface wave feeds on array of radiating elements
915.
[0125] In this illustrative example, the radiation pattern created by antenna
902 is steered in the theta direction by controlling the voltages applied to the different
varactors in array of radiating elements
915. The radiation pattern created by antenna
902 is steered in the phi direction by the slight variations in surface wave index between
neighboring radiating elements. This variation results in phase shifts between the
surface waves propagated along these radiating elements, which results in steering
in the phi direction.
[0126] With reference now to
Figures 11A and
11B, an illustration of yet another configuration for antenna system
900 is depicted in accordance with an illustrative embodiment. In this illustrative example,
phase shifter
904 from
Figure 9 has been replaced with phase shifter
1100.
[0127] Phase shifter
1100 may be used to control the phi steering angle for antenna system
900. Phase shifter
1100 includes waveguides
1102, 1104, 1106, 1108, 1110, 1112, 1114, and
1116. Each of these waveguides is a surface wave waveguide formed by a plurality of metallic
strips and a plurality of varactors located on a dielectric substrate. Voltages may
be applied to at least a portion of the metallic strips on the different dielectric
substrates to control the phase of the surface waves being propagated along these
waveguides to steer the radiation towards the phi steering angle.
[0128] The phase of the surface waves may be controlled such that the phase shift of the
surface waves at the end of the adjacent waveguides is Δψ. The phase of the surface
waves at the end of each of the waveguides is varied by controlling the propagation
speed of the surface waves. The propagation speed of the surface waves may be controlled
by controlling the voltage applied to the varactors on the dielectric substrates.
[0129] Voltage controller
1118 may be used to apply voltages to at least a portion of the metallic strips of the
dielectric substrates, and thereby, at least a portion of the varactors on the dielectric
substrates. Voltage controller
1118 includes digital to analog converter
1120, voltage lines
1122, and ground
1121. Voltages may be applied to at least a portion of the metallic strips on the dielectric
substrates from digital to analog converter
1120 by voltage lines
1122. Another portion of the metallic strips may be grounded to ground
1121. Controller
1123 may be used to control digital to analog converter
1120.
[0130] The phase of the surface waves at the end of a waveguide may be given by the following
equation:
where
nsw(V) is the surface wave index and is dependent on voltage. Each waveguide may be controlled
with a different voltage from voltage controller
1118 in order to create a phase difference at the surface wave feeds on the waveguides.
The radio frequency signals may be sent between the surface wave feeds and radio frequency
module
906 over transmission lines
1124.
[0131] With reference now to
Figure 12, an illustration of a portion of an antenna system is depicted in accordance with
an illustrative embodiment. In this illustrative example, a portion of antenna system
1200 is depicted. Antenna system
1200 is an example of one implementation of antenna system
100 in
Figure 1. As depicted, antenna system
1200 includes radiating element
1201 and radio frequency assembly
1202.
[0132] Radiating element
1201 is an example of one implementation for radiating element
123 in
Figure 1. Further, radiating element
1201 is an example of an implementation for array of radiating elements
122 in
Figure 1 comprising only a single radiating element. Only a portion of radiating element
1201 is shown in this illustrative example. In this example, the radiation pattern produced
by antenna system
1200 may only be electronically scanned in the X-Z plane.
[0133] In this illustrative example, radio frequency assembly
1202 includes radio frequency module
1203, phase shifting device
1204, transmission line
1206, transmission line
1208, surface wave feed
1210, and surface wave feed
1211. Radio frequency module
1203 may be configured to function as a transmitter, a receiver, or a combination of the
two. Phase shifting device
1204 takes the form of a hybrid power splitter in this example. In particular, the hybrid
power splitter is configured for use in varying the phase difference between the radio
frequency signal traveling along transmission line
1206 and the radio frequency signal traveling along transmission line
1208. In this illustrative example, the hybrid power splitter may be used to vary the
phase difference between these two transmission lines between about 0 degrees and
about 90 degrees.
[0134] Of course, in other illustrative examples, radio frequency module
1203 and phase shifting device
1204 may be implemented in some other manner. For example, radio frequency module
1203 may be configured to enable dual polarization with phase shifting device
1204 taking the form of a four port variable phase power splitter.
[0135] Radiating element
1201 is implemented using dielectric substrate
1205. Surface wave channel
1212 and surface wave channel
1213 are formed on dielectric substrate
1205. Surface wave feed
1210 couples transmission line
1206 to surface wave channel
1212. Surface wave feed
1211 couples transmission line
1208 to surface wave channel
1213. Surface wave channel
1212 and surface wave channel
1213 may be examples of implementations for surface wave channel
125 and second surface wave channel
145 in
Figure 1.
[0136] As depicted, surface wave channel
1212 is formed by plurality of metallic strips
1214 and plurality of varactors
1215. In this illustrative example, plurality of metallic strips
1214 are periodically arranged at an angle of about positive 45 degrees relative to X-axis
1216. X-axis
1216 is the longitudinal axis along radiating element
1201. Plurality of varactors
1215 are electrically connected to plurality of metallic strips
1214. Voltage lines
1218 are used to apply voltages to plurality of varactors
1215. Pins
1220 may be used to connect voltage lines
1218 to one or more voltage sources and/or one or more grounds.
[0137] Further, as depicted, surface wave channel
1213 is formed by plurality of metallic strips
1224 and plurality of varactors
1226. As depicted, plurality of metallic strips
1224 are periodically arranged at an angle of about negative 45 degrees relative to X-axis
1216. Voltage lines
1228 are used to apply voltages to plurality of varactors
1226. Pins
1230 are used to connect voltage lines
1228 to one or more voltage sources and/or one or more grounds.
[0138] The radiation pattern formed by radiating element
1201 may be scanned in the X-Z plane by changing the voltages applied to plurality of
varactors
1215 such that the surface wave impedance modulation pattern results in the desired radiation
angle. Surface wave channel
1212 and surface wave channel
1213 are configured such that the radiation from these two surface wave channels may be
orthogonal to each other. The net radiation from the combination of these two surface
wave channels is circularly polarized. When fed by phase shifting device
1204 in the form of a 0°-90° hybrid splitter, surface wave channel
1212 and surface wave channel
1213 are fixed into receiving or transmitting circularly-polarized radiation with either
right-hand polarization or left-hand polarization. Of course, in other illustrative
examples, phase shifting device
1204 may be implemented in some other manner such that the radiation may be switched between
left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP).
[0139] The radiation from surface wave channel
1212 and surface wave channel
1213 is polarized because of the angles at which plurality of metallic strips
1214 and plurality of metallic strips
1224, respectively, are tilted relative to X-axis
1216. Plurality of metallic strips
1214 and plurality of metallic strips
1224 are tensor impedance elements having a major principal axis that is perpendicular
to the long edges of the metallic strips and a minor axis that is along the edges.
The local tensor admittance of each surface wave channel in the coordinate frame of
the principal axes may be given as follows:
where
Ysw is the local tensor admittance and is determined by the voltage applied to the metallic
strips at position x.
[0140] The surface wave current, which is along the major principal axis, is as follows:
where
Jsw is the current of the surface wave and
Esw is the electric field of the surface wave.
[0141] The radiation is driven by the surface wave currents according to the following equation:
and is therefore polarized in the direction across the gaps between the metallic
strips.
Erad is the electric field of the radiation.
[0142] With reference now to
Figure 13, an illustration of antenna system
1200 from
Figure 12 having two radio frequency assemblies is depicted in accordance with an illustrative
embodiment. In this illustrative example, radio frequency assembly
1202 is located at end
1300 of radiating element
1201, while radio frequency assembly
1301 is located at end
1303 of radiating element
1201.
[0143] Radio frequency assembly
1301 includes radio frequency module
1302, phase shifting device
1304, transmission line
1306, transmission line
1308, surface wave feed
1310, and surface wave feed
1312. Surface wave feed
1310 feeds into surface wave channel
1212. Further, surface wave feed
1312 feeds into surface wave channel
1213.
[0144] Either radio frequency assembly
1301 or radio frequency assembly
1202 may function as a sink for any surface wave energy that is not radiated away. In
this manner, surface waves may be prevented from reflecting off at the end of radiating
element
1201, which would lead to undesired distortion of the radiation pattern.
[0145] Further, by having two radio frequency assemblies, the radiation pattern may be more
effectively tuned over a larger angular range. Thus, when radiation is to be tilted
towards the positive portion of X-axis
1216, radio frequency assembly
1202 may be used to feed the radio frequency signal to radiating element
1201. When radiation is to be tilted towards the negative portion of X-axis
1216, radio frequency assembly
1301 may be used to feed the radio frequency signal to radiating element
1201. In this manner, as the radio frequency beam formed by the radiation pattern is scanned
in an angle, beams directed with angles of positive theta and negative theta may be
mirror images of each other.
[0146] With reference now to
Figure 14, an illustration of another antenna system is depicted in accordance with an illustrative
embodiment. In this illustrative example, antenna system
1400 is another example of one implementation for antenna system
100 in
Figure 1. Antenna system
1400 includes antenna
1401, phase shifter
1402, and radio frequency module
1404. Antenna system
1400 may also include a voltage controller (not shown in this example).
[0147] Antenna
1401 includes array of radiating elements
1406 and plurality of surface wave feeds
1407. Array of radiating elements
1406 includes radiating elements
1408, 1410, 1412, 1414, 1416, 1418, 1420, and
1422. Each of these radiating elements may be implemented in a manner similar to radiating
element
1201 in
Figure 12.
[0148] Plurality of surface wave feeds
1407 couple array of radiating elements
1406 to phase shifter
1402. Phase shifter
1402 includes plurality of phase-shifting devices
1424. Transmission lines
1426 connect plurality of surface wave feeds
1407 to plurality of phase-shifting devices
1424 and connect plurality of phase-shifting devices
1424 to radio frequency module
1404. Radio frequency module
1404 may be configured to function as a transmitter, a receiver, or a combination of the
two.
[0149] Plurality of phase-shifting devices
1424 are variable phase shifters in this example. In this illustrative example, plurality
of phase-shifting devices
1424 may be tuned such that the net phase shift at each one of plurality of surface wave
feeds
1407 differs from the phase at a neighboring surface wave feed by a constant, Δφ. As this
constant is varied, the radiation pattern formed may be scanned in the Y-Z plane.
[0150] The illustrations in
Figures 2-14 are not meant to imply physical or architectural limitations to the manner in which
an illustrative embodiment may be implemented. Other components in addition to or
in place of the ones illustrated may be used. Some components may be optional.
[0151] The different components shown in
Figures 2-14 may be illustrative examples of how components shown in block form in
Figure 1 can be implemented as physical structures. Additionally, some of the components in
Figures 2-14 may be combined with components in
Figure 1, used with components in
Figure 1, or a combination of the two.
[0152] In some cases, it may be desirable to improve the gain of an antenna, such as artificial
impedance surface antenna
110 in
Figure 1. The gain of an artificial impedance surface antenna may be improved by improving
the accuracy with which the artificial impedance surface antenna is electronically
steered to reduce fall off in gain. The illustrative embodiments recognize and take
into account that a substantially, radially symmetric arrangement of surface wave
channels may allow more accurate electronic steering of the artificial impedance surface
antenna. Further, with this type of arrangement, the impedance elements used to form
the surface wave channels may be spaced apart greater than half a wavelength. Still
further, this type of arrangement may be used to produce radiation of any polarization.
[0153] With reference now to
Figure 15, an illustration of a different configuration for artificial impedance surface antenna
110 in antenna system
100 from
Figure 1 is depicted in the form of a block diagram in accordance with an illustrative embodiment.
Antenna system
100 from
Figure 1 is depicted with artificial impedance surface antenna
110 having radial configuration
1500.
[0154] When artificial impedance surface antenna
110 has radial configuration
1500, artificial impedance surface antenna
110 includes dielectric substrate
1501, plurality of radiating spokes
1502, and number of surface wave feeds
1504. Dielectric substrate
1501 may be implemented in a manner similar to dielectric substrate
124 in
Figure 1. However, with radial configuration
1500, dielectric substrate
1501 may be the only dielectric substrate used. Dielectric substrate
1501 may be comprised of any number of layers of dielectric material.
[0155] In one illustrative example, dielectric substrate
1501 may be comprised of a material with tunable electrical properties. For example, without
limitation, dielectric substrate
1501 may be comprised of a liquid crystal material.
[0156] In this illustrative example, dielectric substrate
1501 has circular shape
1506 with center point
1508. In other words, dielectric substrate
1501 may be substantially symmetric about center point
1508. In other illustrative examples, dielectric substrate
1501 may have some other shape. For example, without limitation, dielectric substrate
1501 may have an oval shape, a square shape, a hexagonal shape, an octagonal shape, or
some other type of shape. However, when dielectric substrate
1501 is not substantially symmetric about center point
1508, the radiation pattern
112 produced may not have the same gain at different steering angles.
[0157] Plurality of radiating spokes
1502 may be implemented using dielectric substrate
1501. In particular, plurality of radiating spokes
1502 may be formed on dielectric substrate
1501.
[0158] Plurality of radiating spokes
1502 may be arranged radially with respect to center point
1508 of dielectric substrate
1501. In these illustrative examples, being arranged radially with respect to center point
1508 means that each of plurality of radiating spokes
1502 may extend from center point
1508 towards an outer circumference of dielectric substrate
1501. Each of plurality of radiating spokes
1502 may be arranged substantially perpendicular to a center axis through center point
1508 of dielectric substrate
1501. Further, each of plurality of radiating spokes
1502 may be arranged in a manner such that each radiating spoke is substantially symmetric
about center point
1508.
[0159] Each of plurality of radiating spokes
1502 may be implemented in a manner similar to radiating element
123 from
Figure 1. Radiating spoke
1510 may be an example of one implementation for each radiating spoke in plurality of
radiating spokes
1502. Radiating spoke
1510 is configured to form surface wave channel
1512. In this manner, plurality of radiating spokes
1502 may form a plurality of surface wave channels. Surface wave channel
1512 is configured to constrain a path of a surface wave.
[0160] As depicted, radiating spoke
1510 may include plurality of impedance elements
1514 and plurality of tunable elements
1516. Plurality of impedance elements
1514 and plurality of tunable elements
1516 may be implemented in a manner similar to plurality of impedance elements
126 and plurality of tunable elements
128, respectively, from
Figure 1.
[0161] In this illustrative example, plurality of impedance elements
1514 and plurality of tunable elements
1516 may be located on surface
1513 of dielectric substrate
1501. In particular, plurality of impedance elements
1514 and plurality of tunable elements
1516 may be located on surface
1513 of corresponding portion
1515 of dielectric substrate
1501.
[0162] Plurality of impedance elements
1514, plurality of tunable elements
1516, and corresponding portion
1515 of dielectric substrate
1501 may form an artificial impedance surface from which radiation may be generated. In
this illustrative example, corresponding portion
1515 of dielectric substrate
1501 may be considered part of radiating spoke
1510. However, in other illustrative examples, dielectric substrate
1501 may be considered separate from plurality of radiating spokes
1502.
[0163] An impedance element in plurality of impedance elements
1514 may be implemented in a number of different ways. In one illustrative example, an
impedance element may be implemented as a resonating element. In one illustrative
example, an impedance element may be implemented as an element comprised of a conductive
material. The conductive material may be, for example, without limitation, a metallic
material. Depending on the implementation, an impedance element may be implemented
as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic
film, a deposit of a metallic substrate, or some other type of conductive element.
In some cases, an impedance element may be implemented as a resonant structure such
as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR),
a structure comprised of one or more metamaterials, or some other type of structure
or element.
[0164] Each one of plurality of tunable elements
1516 may be an element that can be controlled, or tuned, to change an angle of radiation
pattern
112 produced by radiating spoke
1510. In this illustrative example, each of plurality of tunable elements
1516 may be an element having a capacitance that can be varied based on the voltage applied
to the tunable element.
[0165] In one illustrative example, plurality of impedance elements
1514 takes the form of plurality of metallic strips
1518 and plurality of tunable elements
1516 takes the form of plurality of varactors
1520. Each of plurality of varactors
1520 may be a semiconductor element diode that has a capacitance dependent on the voltage
applied to the semiconductor element diode.
[0166] Plurality of metallic strips
1518 may be arranged in a row on corresponding portion
1515 of dielectric substrate
1501 substantially parallel to a plane that is substantially perpendicular to a center
axis through center point
1508 of dielectric substrate
1501. For example, plurality of metallic strips
1518 may be periodically distributed on corresponding portion
1515 of dielectric substrate
1501 along an axis that is substantially perpendicular to and that passes through the
center axis through dielectric substrate
1501.
[0167] In some illustrative examples, plurality of metallic strips
1518 may be printed onto dielectric substrate
1501. For example, plurality of metallic strips
1518 may be printed onto dielectric substrate
1501 using any number of three-dimensional printing techniques, additive deposition techniques,
inkjet deposition techniques, or other types of printing techniques.
[0168] Plurality of varactors
1520 may be electrically connected to plurality of metallic strips
1518 on surface
1513 of corresponding portion
1515 of dielectric substrate
1501. As one illustrative example, at least one varactor in plurality of varactors
1520 may be positioned between each adjacent pair of metallic strips in plurality of metallic
strips
1518. Further, plurality of varactors
1520 may be aligned such that all of the varactor connections on each metallic strip have
the same polarity.
[0169] Voltages may be applied to plurality of tunable elements
1516 by applying voltages to plurality of impedance elements
1514. In particular, varying the voltages applied to plurality of impedance elements
1514 varies the capacitance of plurality of tunable elements
1516. Varying the capacitances of plurality of tunable elements
1516 may vary, or modulate, the capacitive coupling and impedance between plurality of
impedance elements
1514.
[0170] Corresponding portion
1515 of dielectric substrate
1501, plurality of impedance elements
1514, and plurality of tunable elements
1516 may be configured with respect to selected design configuration
1522 for surface wave channel
1512 formed by radiating spoke
1510. Depending on the implementation, each radiating spoke in plurality of radiating
spokes
1502 may have a same or different selected design configuration.
[0171] As depicted, selected design configuration
1522 for radiating spoke
1510 may include a number of design parameters such as, but not limited to, impedance
element width
1524, impedance element spacing
1526, tunable element spacing
1528, and substrate thickness
1530. Impedance element width
1524 may be the width of an impedance element in plurality of impedance elements
1514. Impedance element width
1524 may be selected to be the same or different for each of plurality of impedance elements
1514, depending on the implementation.
[0172] Impedance element spacing
1526 may be the spacing of plurality of impedance elements
1514 along surface
1513 of corresponding portion
1515 of dielectric substrate
1501. Tunable element spacing
1528 may be the spacing of plurality of tunable elements
1516 along surface
1513 of corresponding portion
1515 of dielectric substrate
1501. Further, substrate thickness
1530 may be the thickness of corresponding portion
1515 of dielectric substrate
1501. In this illustrative example, an entirety of dielectric substrate
1501 may have a substantially same thickness. However, in other illustrative examples,
the different portions of dielectric substrate
1501 corresponding to the different radiating spokes in plurality of radiating spokes
1502 may have different thicknesses.
[0173] The values for the different parameters in selected design configuration
1522 may be selected based on, for example, without limitation, the radiation frequency
at which artificial impedance surface antenna
110 is configured to operate. Other considerations include, for example, the desired
impedance modulations for artificial impedance surface antenna
110.
[0174] The surface waves propagated along each of plurality of radiating spokes
1502 may be coupled to number of transmission lines
156 by number of surface wave feeds
1504 located on dielectric substrate
1501. Each of number of surface wave feeds
1504 couples at least one corresponding radiating spoke in plurality of radiating spokes
1502 to a transmission line that carries a radio frequency signal, such as one of number
of transmission lines
156.
[0175] A surface wave feed in number of surface wave feeds
1504 may be any device that is capable of converting a surface wave into a radio frequency
signal, a radio frequency signal into a surface wave, or both. In one illustrative
example, a surface wave feed in number of surface wave feeds
1504 may be located substantially at center point
1508 of dielectric substrate
1501.
[0176] In one illustrative example, number of surface wave feeds
1504 takes the form of a single surface wave feed positioned at center point
1508 of dielectric substrate
1501. This single surface wave feed, which may be referred to as a central feed, may couple
each of plurality of radiating spokes
1502 to number of transmission lines
156. In this example, number of transmission lines
156 may take the form of a coaxial cable.
[0177] In another illustrative example, number of surface wave feeds
1504 may take the form of a plurality of surface wave feeds located at or near center
point
1508 and configured to couple plurality of radiating spokes
1502 to number of transmission lines
156. In this example, number of transmission lines
156 may take the form of a single transmission line or a plurality of transmission lines.
[0178] When artificial impedance surface antenna
110 is in a receiving mode, electromagnetic radiation received at artificial impedance
surface antenna
110 may be propagated as surface waves along plurality of radiating spokes
1502. These surface waves are received by number of surface wave feeds
1504 and converted into number of radio frequency signals
1532. Number of radio frequency signals
1532 may be sent to radio frequency module
108 over one or more of number of transmission lines
156. Radio frequency module
108 may then process number of radio frequency signals
1532 accordingly.
[0179] When artificial impedance surface antenna
110 is in a transmitting mode, number of radio frequency signals
1532 may be sent from radio frequency module
108 to artificial impedance surface antenna
110 over number of transmission lines
156. In particular, number of radio frequency signals
1532 may be received at number of surface wave feeds
1504 and converted into surface waves that are propagated along plurality of radiating
spokes
1502.
[0180] Radiation pattern
112 of artificial impedance surface antenna
110 may be electronically steered in both a theta direction and a phi direction. Radiation
pattern
112 may be formed by number of radiation sub-patterns
1533. Number of radiation sub-patterns
1533 may be produced by a corresponding portion of plurality of radiating spokes
1502. This corresponding portion may be one or more of plurality of radiating spokes
1502. In some cases, number of radiation sub-patterns
1533 may be produced by all of plurality of radiating spokes
1502.
[0181] For example, number of radiation sub-patterns
1533 may be produced by a corresponding number of radiating spokes in plurality of radiating
spokes
1502. Each of number of radiation sub-patterns
1533 is the radiation pattern produced by a particular radiating spoke. Number of radiating
sub-patterns
1533 forms radiation pattern
112. For example, when number of radiating sub-patterns
1533 includes multiple radiating sub-patterns corresponding to multiple radiating spokes,
the combination and overlapping of these multiple radiation sub-patterns forms radiation
pattern
112.
[0182] In this illustrative example, each of plurality of radiating spokes
1502 may be independently controlled such that each of number of radiation sub-patterns
1533 may be electronically steered. For example, without limitation, radiating spoke
1510 may have radiation sub-pattern
1534. Radiation sub-pattern
1534 may be controlled independently of the other radiation sub-patterns formed by the
other radiating spokes in plurality of radiating spokes
1502.
[0183] As one illustrative example, voltage controller
104 may be used to control the voltages applied to plurality of tunable elements
1516 to control both the theta and phi steering angles of a main lobe of radiation sub-pattern
1534. Similarly, voltage controller
104 may be configured to control the voltages applied to the plurality of tunable elements
in each of plurality of radiating spoke
1502 to control both the theta and phi steering angles of a main lobe of the radiation
sub-pattern formed by each of plurality of radiating spokes
1502.
[0184] Thus, each of number of radiation sub-patterns
1533 may be directed in a particular theta direction and a broad phi direction. For example,
a particular radiation sub-pattern may be directed at a theta steering angle of about
45 degrees and may fan out over a broad range of phi angles. In this manner, each
radiation sub-pattern may form, for example, a fan beam.
[0185] Number of radiation sub-patterns
1533 overlap to form radiation pattern
112 having main lobe
116 directed in a particular phi direction and a particular theta direction. Radiation
pattern
112 may be formed such that a beam of radiation is produced. The beam may take the form
of, for example, a pencil beam that is directed at a particular phi steering angle
118 and a particular theta steering angle
120. In this manner, artificial impedance surface antenna
110 may be electronically steered in two dimensions.
[0186] Depending on the implementation, artificial impedance surface antenna
110 may be configured to emit linearly polarized radiation or circularly polarized radiation.
In other words, artificial impedance surface antenna
110 may be used to produce radiation pattern
112 that is linearly polarized or circularly polarized. Further, radiation pattern
112 may be switched between being linearly polarized and circularly polarized by adjusting
the voltages applied to plurality of tunable elements
1516 and without needing to change a physical configuration of artificial impedance surface
antenna
110.
[0187] The impedance sub-patterns produced by the surface wave channels formed by plurality
of radiating spokes
1502 may be modulated to produce overall radiation pattern
112 that is linearly polarized. For example, the voltages applied to the tunable elements
of each of a corresponding portion of plurality of radiating spokes
1502 may be set such that the impedance sub-pattern produced along the surface wave channel
formed by each radiating spoke is given as follows:
where θ
0 is the theta angle of the main lobe of the radiation pattern, Ø
0 is the phi angle of the main lobe of the radiation pattern,
ØSWC is the polar angle of the line that extends along a center of the surface wave channel,
r is the radial distance along the surface wave channels,
X and
M are the mean impedance and the amplitude, respectively, of the modulation of artificial
impedance surface antenna
110, and
Z(
r,ØSWC) is the impedance sub-pattern produced along the surface wave channel. This impedance
sub-pattern may produce radiation that is linearly polarized in the direction of the
theta unit vector, θ̂, where:
[0188] In other examples, the impedance sub-patterns of the surface wave channels formed
by plurality of radiating spokes
1502 may be modulated to produce overall radiation pattern
112 that is circularly polarized. The voltages applied to the tunable elements of each
of a corresponding portion of plurality of radiating spokes
1502 may be set such that the impedance sub-pattern produced by the surface wave channel
formed by each radiating spoke is given as follows:
where
where the "+" of ± indicates the impedance pattern that produces left-handed circular
polarization, and the "-" of ± indicates the impedance pattern that produces right-handed
circular polarization.
[0189] Equation 15 may be approximated as follows:
[0190] In other illustrative examples, the impedance sub-patterns may be given by other
types of equations involving periodic functions. For example, the sine function of
sin(γ ± ϕ) in Equation (19), the sine function of sin(γ ± γ
0) in Equation (15), and the cosine function of cos(
k0r(n0 - cos(Ø
SWC - Ø
0) sin(θ
0)) in Equation (13) may each be replaced by some other type of periodic function.
[0191] In this manner, artificial impedance surface antenna
110 may be used to produce radiation of any polarization without requiring a change in
the physical configuration of artificial impedance surface antenna
110. Artificial impedance surface antenna
110 may be used to produce linearly polarized or circularly polarized radiation just
by changing the voltages applied to the tunable elements of plurality of radiating
spokes
1502.
[0192] Depending on the implementation, artificial impedance surface antenna
110 may propagate surface waves towards or away from center point
1508 of dielectric substrate
1501. In some illustrative examples, artificial impedance surface antenna
110 may include absorption material
1536 when the surface waves are propagated away from center point
1508. Absorption material
1536 may be located at and around an edge of dielectric substrate
1501. Absorption material
1536 is configured to absorb excess energy from the surface waves propagated radially
outward away from center point
1508 through plurality of radiating spokes
1502.
[0193] In some illustrative examples, dielectric substrate
1501 may be grounded using grounding element
1538. In particular, grounding element
1538 may be located at an impedance surface of dielectric substrate
1501.
[0194] The illustration of antenna system
100 in
Figure 1 is not meant to imply physical or architectural limitations to the manner in which
an illustrative embodiment may be implemented. Other components in addition to or
in place of the ones illustrated may be used. Some components may be optional. Also,
the blocks are presented to illustrate some functional components. One or more of
these blocks may be combined, divided, or combined and divided into different blocks
when implemented in an illustrative embodiment.
[0195] In some illustrative examples, a tunable element in plurality of tunable elements
1516 may be implemented as a pocket of variable material embedded in dielectric substrate
1501.
[0196] In other illustrative examples, a tunable element in plurality of tunable elements
1516 may be part of a corresponding impedance element in plurality of impedance elements
1514. For example, a resonant structure having a tunable element may be used. The resonant
structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled
resonator, or some other type of resonant structure.
[0197] In other illustrative examples, center point
1508 may be the center point about which plurality of radiating spokes
1502 are arranged but may not be the geometric center of dielectric substrate
1501. For example, center point
1508 may be offset from the geometric center of dielectric substrate
1501.
[0198] In yet other illustrative examples, each of plurality of radiating spokes
1502 may have two independently controllable portions configured to form a surface wave
channel. For example, radiating spoke
1510 may have a first portion that extends in one direction away from center point
1508 and a second portion that extends in the substantially opposite direction away from
center point
1508. These two portions may have a same or different design configuration, depending
on the implementation. Further, these two portions may be individually referred to
as radiating spokes or radiating sub-spokes in some cases.
[0199] With reference now to
Figure 16, an illustration of an artificial impedance surface antenna is depicted in accordance
with an illustrative embodiment. In this illustrative example, artificial impedance
surface antenna
1600 may be an example of one implementation for artificial impedance surface antenna
110 having radial configuration
1500 in
Figure 15. Artificial impedance surface antenna
1600 has radial configuration
1601, which may be an example of one implementation for radial configuration
1500 in
Figure 15.
[0200] As depicted, artificial impedance surface antenna
1600 includes dielectric substrate
1602, central surface wave feed
1604, and plurality of radiating spokes
1606. Dielectric substrate
1602, central surface wave feed
1604, and plurality of radiating spokes
1606 may be examples of implementations for dielectric substrate
1501, number of surface wave feeds
1504, and plurality of radiating spokes
1502, respectively, in
Figure 15.
[0201] In this illustrative example, dielectric substrate
1602 has a circular shape with center point
1605. Plurality of radiating spokes
1606 are arranged radially with respect to center point
1605 such that artificial impedance surface antenna
1600 is substantially radially symmetric. Radiating spoke
1608, radiating spoke
1610, radiating spoke
1612, and radiating spoke
1614 may be examples of some of plurality of radiating spokes
1606.
[0202] Plurality of radiating spokes
1606 are formed by impedance elements
1616 that have been printed on dielectric substrate
1602. Impedance elements
1616 take the form of metallic strips in this illustrative example. Plurality of radiating
spokes
1606 may also include tunable elements (not shown in this view) located between impedance
elements
1616.
[0203] Central surface wave feed
1604 may couple plurality of radiating spokes
1606 to a transmission line (not shown in this view). The transmission line may be configured
to carry a radio frequency to, from, or both to and from central surface wave feed
1604.
[0204] Artificial impedance surface antenna
1600 may be electronically steered with a desired level of accuracy in a theta direction
and a phi direction. Each of plurality of radiating spokes
1606 may be individually electronically steered in a particular theta direction and a
broad phi direction to produce a fan beam. For example, radiating spoke
1608, radiating spoke
1612, and radiating spoke
1614 may be electronically steered to produce fan beam
1618, fan beam
1620, and fan beam
1622, respectively. The radiation patterns corresponding to fan beam
1618, fan beam
1620, and fan beam
1622 may overlap such that pencil beam
1624 is produced. Pencil beam
1624 may be directed at a particular theta steering angle and a particular phi steering
angle.
[0205] As depicted, absorption material
1626 is located at and around an outer edge of dielectric substrate
1602. Absorption material
1626 may be an example of one implementation for absorption material
1536 in
Figure 15. Absorption material
1626 is configured to absorb excess energy resulting from surface waves propagating away
from center point
1605.
[0206] With reference now to
Figure 17, an illustration of a cross-sectional side view of artificial impedance surface antenna
1600 from
Figure 16 is depicted in accordance with an illustrative embodiment. In this illustrative example,
a cross-sectional side view of artificial impedance surface antenna
1600 from
Figure 16 is depicted taken with respect to cross-section lines
17-17 in
Figure 17.
[0207] In this illustrative example, grounding element
1700 may be seen along the surface of dielectric substrate
1602. Grounding element
1700 is an example of one implementation for grounding element
1538 in
Figure 15.
[0208] Transmission line
1702 is also shown in this view. Transmission line
1702 may carry a radio frequency to, from, or both to and from central surface wave feed
1604. In one illustrative example, transmission line
1702 takes the form of a coaxial cable.
[0209] As depicted, surface waves may propagate in the direction of arrow
1704, substantially parallel to dielectric substrate
1602 and substantially perpendicular to center axis 1706 through center point
1605 of dielectric substrate
1602. Plurality of radiating spokes 1606 (not shown in this view) may be arranged such
that plurality of radiating spokes
1606 are substantially symmetric about center axis
1706.
[0210] With reference now to
Figure 18, an illustration of an impedance pattern for artificial impedance surface antenna
1600 from
Figures 16-17 is depicted in accordance with an illustrative embodiment. In this illustrative example,
impedance pattern
1800 may be produced when artificial impedance surface antenna
1600 is linearly polarized and configured to produce a radiation pattern having a main
lobe directed at a theta steering angle of about 45 degrees and a phi steering angle
of about 0 degrees.
[0211] Impedance pattern
1800 is shown with respect to first axis
1802 and second axis
1804. First axis
1802 and second axis
1804 may represent the two axes that form the plane substantially parallel to dielectric
substrate
1602 in
Figure 16. Impedance pattern
1800 is comprised of impedance sub-patterns
1806 formed by plurality of radiating spokes
1606 in
Figures 16. Scale
1808 provides the correlation between the impedance sub-patterns
1806 and impedance values. The impedance values may be in units of j-Ohms in which j is
equal to
[0212] With reference now to
Figure 19, an illustration of a portion of an artificial impedance surface antenna is depicted
in accordance with an illustrative embodiment. In this illustrative example, artificial
impedance surface antenna
1900 may be another example of one implementation for artificial impedance surface antenna
110 having radial configuration
1500 in
Figure 15. Artificial impedance surface antenna
1900 has radial configuration
1901, which may be an example of one implementation for radial configuration
1500 in
Figure 15.
[0213] In this illustrative example, artificial impedance surface antenna
1900 includes dielectric substrate
1902, radiating spokes
1904, and central surface wave feed
1906. Only a portion of the total plurality of radiating spokes that form artificial impedance
surface antenna
1900 are shown in this view.
[0214] Radiating spoke
1907 is an example of one of radiating spokes
1904. Only a portion of radiating spoke
1907 is shown. Radiating spoke
1907 is located on corresponding portion
1908 of dielectric substrate
1902. Radiating spoke
1907 includes plurality of metallic strips
1909 and plurality of varactors
1910. Plurality of metallic strips
1909 and plurality of varactors
1910 may be an example of one implementation for plurality of metallic strips
1518 and plurality of varactors
1520, respectively, in
Figure 15.
[0215] As depicted, voltages may be applied to plurality of metallic strips
1909, and thereby plurality of varactors
1910, through conductive lines
1912, which terminate at terminals
1914. Terminals
1914 may be connected to electrical vias (not shown in this view) that pass through the
thickness of dielectric substrate
1902 and through a grounding element (not shown in this view) to connectors that connect
to control hardware, such as a voltage controller.
[0216] With reference now to
Figure 20, an illustration of a cross-sectional side view of artificial impedance surface antenna
1900 from
Figure 19 is depicted in accordance with an illustrative embodiment. In this illustrative example,
a cross-sectional side view of artificial impedance surface antenna
1900 from
Figure 19 is depicted taken with respect to cross-section lines
20-20 in
Figure 19.
[0217] In this illustrative example, electrical vias
2000 that connect terminals
1914 in
Figure 19 to voltage controller
2002 are shown. Voltage controller
2002 may vary the voltages applied to the metallic strips of plurality of radiating spokes
1904 in
Figure 19.
[0218] The illustrative embodiments recognize and take into account that different types
of configurations for artificial impedance surface antenna
110 in
Figure 1 may improve the efficiency and thereby, overall performance, of artificial impedance
surface antenna
110. For example, the illustrative embodiments recognize and take into account that in
some cases, it may be desirable to provide a square-wave-type profile of surface impedance
across each surface wave channel formed on each radiating element of artificial impedance
surface antenna
110 in
Figure 1.
[0219] The illustrative embodiments recognize that using switch elements that have only
two possible states as compared to varactors that can be tuned to have any of various
capacitance states across a range of capacitance values may enable achieving a square-wave-type
profile of surface impedance for a surface wave channel. These switch elements may
take the form of, for example, without limitation, PIN diodes.
[0220] With reference now to
Figure 21, an illustration of artificial impedance surface antenna
110 from
Figure 1 is depicted in the form of a block diagram in accordance with an illustrative embodiment.
In this illustrative example, at least one surface wave channel on at least one radiating
element in artificial impedance surface antenna
110 in
Figure 21 may be implemented differently than as described in
Figure 1.
[0221] As depicted, surface wave channel
125 from
Figure 1 may not include plurality of tunable elements
128 from
Figure 1. Rather, in this illustrative example, surface wave channel
125 includes plurality of switch elements
2100 instead of plurality of tunable elements
128 from
Figure 1. Each of plurality of switch elements
2100 may have only two states
2102. Two states
2102 may include first state
2104 and second state
2106. In some cases, first state
2104 may be referred to as an on state and second state
2106 may be referred to as an off state.
[0222] In one illustrative example, plurality of switch elements
2100 takes the form of plurality of PIN diodes
2108. In other illustrative examples, a switch element in plurality of switch elements
2100 may be selected from one of a semiconductor switch, a microelectromechanical systems
(MEMS) switch, a high frequency diode, a Schottky diode, and a phase-change material
switch.
[0223] Switch element
2101 may be an example of one of plurality of switch elements
2100. Switch element
2101 may be placed within the gap between first impedance element
2113 of plurality of impedance elements
126 and second impedance element
2115 of plurality of impedance elements
126. Further, switch element
2101 may electrically connect first impedance element
2113 to second impedance element
2115. The capacitance of switch element
2101 and the capacitance of the gap between first impedance element
2113 and second impedance element
2115 contribute to the total capacitance between first impedance element
2113 and second impedance element
2115. In some cases, the capacitance of the gap between first impedance element
2113 and second impedance element
2115 may be negligible.
[0224] When switch element
2101 takes the form of a PIN diode, first state
2104 may take the form of inductance state
2105 and second state
2106 may take the form of capacitance state
2107. Switch element
2101 may be placed in inductance state
2105 by applying a first level of voltage to switch element
2101. Switch element
2101 may be placed in capacitance state
2107 by applying a second level of voltage to switch element
2101.
[0225] Whether switch element
2101 is in inductance state
2105 or in capacitance state
2107 may be determined by the reactance of switch element
2101. For example, the surface impedance associated with switch element
2101 may be defined as follows:
where R is resistance and is the real part of the surface impedance and where X is
reactance and is the imaginary part of the surface impedance. The resistance may also
be referred to as surface resistance and the reactance may also be referred to as
surface reactance. When the reactance is positive, the reactance is described as inductive
and switch element
2101 may be considered in inductance state
2105. When the reactance is negative, the reactance is described as capacitive and switch
element
2101 may be considered in capacitance state
2107. When the reactance is substantially zero, the surface impedance may be considered
substantially purely resistive.
[0226] In inductance state
2105, switch element
2101 may have substantially zero capacitance but may have parasitic inductance. In other
words, the capacitance of switch element
2101 may be zero or negligible when switch element
2101 is in inductance state
2105. In this manner, in inductance state
2105, switch element
2101 may be modeled as a series resistor-inductor circuit. In capacitance state
2107, switch element
2101 may have some selected non-zero capacitance value. In this manner, in capacitance
state
2107, switch element
2101 may be modeled as a parallel resistor-capacitor circuit.
[0227] Because each of plurality of switch elements
2100 may have only one of two states
2102 at any given point in time, the voltages applied to plurality of switch elements
2100 may be used to create surface impedance profile
2114 for surface wave channel
125. In particular, one of two levels of voltage may be applied to each of plurality
of switch elements
2100 to create surface impedance profile
2114. Surface impedance profile
2114 may be created such that only a selected high surface impedance, a selected low surface
impedance, or some combination of the two is formed.
[0228] For example, without limitation, the voltages applied to plurality of switch elements
2100 may be controlled such that surface impedance profile
2114 takes the form of square-wave modulation
2110 of high surface impedance and low surface impedance. Square-wave modulation
2110 may be a square-wave-type modulation. In other words, in one illustrative example,
the state of each of plurality of switch elements
2100 may be controlled to modulate high surface impedance and low surface impedance in
the form of a square-wave as compared to a sinusoidal wave. These two surface impedance
levels may be modulated over each surface wave channel on each radiating element of
artificial impedance surface antenna
110 to electronically steer artificial impedance surface antenna
110 in a theta direction, a phi direction, or both.
[0229] In one illustrative example, each of plurality of impedance elements
126 may take the form of a rectangular metallic strip. In some illustrative examples,
each of plurality of impedance elements
126 may have a shape that has repeating pattern
2112. Repeating pattern
2112 may be a pattern of shapes. For example, a particular impedance element of plurality
of impedance elements
126 may have a repeating pattern of a same shape that is selected from one of a hexagonal-type
shape, a diamond-type shape, or some other type of shape.
[0230] Using plurality of switch elements
2100 for surface wave channel
125 may improve the gain of artificial impedance surface antenna
110. Further, using plurality of switch elements
2100 may enable artificial impedance surface antenna
110 to be operated at a frequency in the Ka-band with a desired level of aperture efficiency.
In this manner, using plurality of switch elements
2100 may reduce power loss. The Ka-band may include frequencies between about 26.5 gigahertz
and about 40 gigahertz. As one illustrative example, using plurality of PIN diodes
2108 may enable artificial impedance surface antenna
110 to be operated at a frequency of about 30 gigahertz with greater than about 25 percent
aperture efficiency.
[0231] The illustration of artificial impedance surface antenna
110 in
Figure 21 is not meant to imply physical or architectural limitations to the manner in which
an illustrative embodiment may be implemented. Other components in addition to or
in place of the ones illustrated may be used. Some components may be optional. Also,
the blocks are presented to illustrate some functional components. One or more of
these blocks may be combined, divided, or combined and divided into different blocks
when implemented in an illustrative embodiment.
[0232] With reference now to
Figure 22, an illustration of a radiating element is depicted in accordance with an illustrative
embodiment. In this illustrative example, radiating element
2200 may be an example of one implementation for radiating element
123 in
Figure 21.
[0233] As depicted, radiating element
2200 includes dielectric substrate
2202. Surface wave channel
2204 is formed on dielectric substrate
2202. Surface wave channel
2204 may be an example of one implementation for surface wave channel
125 in
Figure 21.
[0234] In this illustrative example, surface wave channel
2204 comprises plurality of impedance elements
2206 and plurality of switch elements
2208. Plurality of switch elements
2208 may be an example of one implementation for plurality of switch elements
2100 in
Figure 21.
[0235] Each of plurality of switch elements
2208 may have only one of two states at any given point in time in this illustrative example.
For example, when one of plurality of switch elements
2208 is in an on state, the switch element may function in a manner similar to a circuit
comprising a resistor and inductor in series. The on state corresponds to high surface
impedance. The inductance that is provided may be important to enable operation of
the artificial surface impedance antenna to which surface wave channel
2204 belongs within the Ka-band of frequencies. When the switch element is in an off state,
the switch element may function in a manner similar to a circuit comprising a resistor
and capacitor in parallel. The off state corresponds to low surface impedance.
[0236] The state of each of plurality of switch elements
2208 may be controlled to modulate between high surface impedance and low surface impedance
to create a surface impedance profile for surface wave channel
2204. In this illustrative example, this surface impedance profile may resemble a square-wave-type
modulation. Portion
2210 of surface wave channel
2204 is shown enlarged in
Figure 23 below.
[0237] With reference now to
Figure 23, an illustration of an enlarged view of portion
2210 of surface wave channel
2204 from
Figure 22 is depicted in accordance with an illustrative embodiment. As depicted, plurality
of impedance elements
2206 includes impedance element
2300 and impedance element
2302. Impedance element
2300 and impedance element
2302 may be examples of implementations for first impedance element
2113 and second impedance element
2115, respectively, from
Figure 21.
[0238] Plurality of switch elements
2208 includes set of switch elements
2304 positioned within the gap between impedance element
2300 and impedance element
2302. Each of set of switch elements
2304 has only two possible states and may be in only one of these two possible states
at any given point in time. In one illustrative example, these two states may be an
inductance state and a capacitance state.
[0239] As depicted, set of switch elements
2304 includes switch element
2306, switch element
2308, and switch element
2310. Switch element
2306, switch element
2308, and switch element
2310 electrically connect impedance element
2300 and impedance element
2302.
[0240] Each of plurality of impedance elements
2206 in
Figure 22 may have a repeating pattern of shapes. For example, impedance element
2302 has repeating pattern
2312. Repeating pattern
2312 is a series of same shapes. In this illustrative example, repeating pattern
2312 is a series of hexagonal-type shapes. As depicted, repeating pattern
2312 includes hexagonal-type shape
2314, hexagonal-type shape
2316, and hexagonal-type shape
2318.
[0241] With reference now to
Figure 24, an illustration of another configuration for a radiating element is depicted in
accordance with an illustrative embodiment. In this illustrative example, radiating
element
2400 may be an example of one implementation for radiating element
123 in
Figure 21.
[0242] As depicted, radiating element
2400 includes dielectric substrate
2402. Surface wave channel
2404 is formed on dielectric substrate
2402. Surface wave channel
2404 may be an example of one implementation for surface wave channel
125 in
Figure 21. Surface wave channel
2404 comprises plurality of impedance elements
2406 and plurality of switch elements
2408.
[0243] Plurality of impedance elements
2406 may be an example of one implementation for plurality of impedance elements
126 in
Figure 1. In this illustrative example, each of plurality of impedance elements
2406 may take the form of a rectangular metallic strip.
[0244] Plurality of switch elements
2408 may be an example of one implementation for plurality of switch elements
2100 in
Figure 21. In this illustrative example, each of plurality of switch elements
2408 may have only one of two states at any given point in time. In one illustrative example,
each of plurality of switch elements
2408 may be implemented in the form of a PIN diode.
[0245] For example, when one of plurality of switch elements
2408 is in an on state, the switch element may function in a manner similar to a circuit
comprising a resistor and inductor in series. The on state corresponds to high surface
impedance. The inductance that is provided may be important to enable operating within
the Ka-band of frequencies. When the switch element is in an off state, the switch
element may function in a manner similar to a circuit comprising a resistor and capacitor
in parallel. The off state corresponds to low surface impedance.
[0246] The illustrations in
Figures 22-24 are not meant to imply physical or architectural limitations to the manner in which
an illustrative embodiment may be implemented. Other components in addition to or
in place of the ones illustrated may be used. Some components may be optional.
[0247] The different components shown in
Figures 22-24 may be illustrative examples of how components shown in block form in
Figures 1 and
2 can be implemented as physical structures. Additionally, some of the components in
Figures 22-24 may be combined with components in
Figures 1 and
2, used with components in
Figures 1 and
2, or a combination of the two.
[0248] Turning now to
Figure 25, an illustration of a process for electronically steering an antenna system is depicted
in the form of a flowchart in accordance with an illustrative embodiment. The process
illustrated in
Figure 25 may be implemented to electronically steer antenna system
100 in
Figure 1.
[0249] The process begins by propagating a surface wave along each of a number of surface
wave channels formed in each of a plurality of radiating elements to form a radiation
pattern (operation
2500). Each surface wave channel in the number of surface wave channels formed in each
radiating element in the plurality of radiating elements is coupled to a transmission
line configured to carry a radio frequency signal using a surface wave feed in a plurality
of surface wave feeds associated with the plurality of radiating elements (operation
2502).
[0250] Thereafter, a main lobe of the radiation pattern is electronically steered in a theta
direction by controlling voltages applied to the number of surface wave channels in
each radiating element in the plurality of radiating elements (operation
2504). Further, the main lobe of the radiation pattern is electronically steered in a
phi direction by controlling a relative phase difference between the plurality of
surface wave feeds (operation
2506), with the process terminating thereafter.
[0251] With reference now to
Figure 26, an illustration of a process for electronically steering an antenna system is depicted
in the form of a flowchart in accordance with an illustrative embodiment. The process
illustrated in
Figure 26 may be implemented to electronically steer, for example, artificial impedance surface
antenna
110 having radial configuration
1500 in
Figure 15.
[0252] The process begins by propagating a surface wave along a plurality of surface wave
channels formed by a plurality of radiating spokes in an antenna to generate a number
of radiation sub-patterns in which the plurality of radiating spokes is arranged radially
with respect to a center point of a dielectric substrate (operation
2600). Next, a main lobe of a radiation pattern of the antenna is electronically steered
in two dimensions (operation
2602), with the process terminating thereafter.
[0253] With reference now to
Figure 27, an illustration of a process for electronically steering an antenna system is depicted
in the form of a flowchart in accordance with an illustrative embodiment. The process
illustrated in
Figure 27 may be implemented to electronically steer, for example, artificial impedance surface
antenna
110 having switch elements as described in
Figure 21.
[0254] The process begins by propagating a surface wave along each of a number of surface
wave channels formed in each of a plurality of radiating elements to form a radiation
pattern (operation
2700). Next, each surface wave channel in the number of surface wave channels formed in
each radiating element in the plurality of radiating elements may be coupled to a
transmission line configured to carry a radio frequency signal using a surface wave
feed in a plurality of surface wave feeds associated with the plurality of radiating
elements (operation
2702).
[0255] A main lobe of the radiation pattern may be electronically steered by controlling
voltages applied to a plurality of switch elements connecting a plurality of impedance
elements in each of the number of surface wave channels (operation
2704), with the process terminating thereafter.
[0256] The flowcharts and block diagrams in the different depicted embodiments illustrate
the architecture, functionality, and operation of some possible implementations of
apparatuses and methods in an illustrative embodiment. In this regard, each block
in the flowcharts or block diagrams may represent a module, a segment, a function,
and/or a portion of an operation or step.
[0257] In some alternative implementations of an illustrative embodiment, the function or
functions noted in the blocks may occur out of the order noted in the figures. For
example, in some cases, two blocks shown in succession may be executed substantially
concurrently, or the blocks may sometimes be performed in the reverse order, depending
upon the functionality involved. Also, other blocks may be added in addition to the
illustrated blocks in a flowchart or block diagram.
[0258] Further, the disclosure comprises embodiments according to the following clauses:
Clause 1: An apparatus comprising: a plurality of radiating elements, wherein each
radiating element in the plurality of radiating elements comprises a number of surface
wave channels in which each of the number of surface wave channels is configured to
constrain a path of a surface wave and comprises: a plurality of switch elements;
and a plurality of impedance elements; and a plurality of surface wave feeds, wherein
a surface wave feed in the plurality of surface wave feeds is configured to couple
a surface wave channel in the number of surface wave channels of a radiating element
in the plurality of radiating elements to a transmission line configured to carry
a radio frequency signal.
Clause 2: The apparatus of clause 1, wherein the plurality of radiating elements and
the plurality of surface wave feeds form an artificial impedance surface antenna that
is configured to be electronically steered in a theta direction and a phi direction.
Clause 3: The apparatus of clause 2, wherein the artificial impedance surface antenna
operates at a frequency between about 26.5 gigahertz and about 40 gigahertz.
Clause 4: The apparatus of clause 2, wherein the artificial impedance surface antenna
operates at a frequency of about 30 gigahertz with an aperture efficiency greater
than about 25 percent.
Clause 5: The apparatus of clause 2, wherein the plurality of switch elements of each
surface wave channel of the number of surface wave channels enables creating a surface
impedance profile of high surface impedance and low surface impedance for the each
surface wave channel.
Clause 6: The apparatus of clause 5, wherein the surface impedance profile is a square-wave-type
modulation.
Clause 7: The apparatus of clause 5, wherein the high surface impedance and the low
surface impedance are modulated to enable scanning in the theta direction and in the
phi direction.
Clause 8: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a PIN diode that has an inductance state and a capacitance state.
Clause 9: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a Schottky diode that has only two states.
Clause 10: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a semiconductor switch that has only two states.
Clause 11: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a microelectromechanical systems switch diode that has only
two states.
Clause 12: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a phase-change material switch that has only two states.
Clause 13: The apparatus of clause 1, wherein each switch element in the plurality
of switch elements is a high frequency diode that has only two states.
Clause 14: The apparatus of clause 1, wherein an impedance element in the plurality
of impedance elements is selected from one of a metallic strip, a patch of conductive
paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate,
a resonant structure, a split-ring resonator, and an electrically-coupled resonator,
a structure comprised of one or more metamaterials.
Clause 15: The apparatus of clause 1, wherein an impedance element in the plurality
of impedance elements has a pattern formed by a series of a same shape.
Clause 16: The apparatus of clause 15, wherein the same shape is selected from one
of a diamond-type shape and a hexagonal-type shape.
Clause 17: An artificial impedance surface antenna comprising: a plurality of radiating
elements, wherein each of the plurality of radiating elements comprises a number of
surface wave channels in which each of the number of surface wave channels is configured
to constrain a path of a surface wave and comprises: a plurality of impedance elements
located on a surface of a dielectric substrate; and a plurality of switch elements
located on the surface of the dielectric substrate in which each of the plurality
of switch elements has a first state and a second state; and a plurality of surface
wave feeds configured to couple the number of surface wave channels of each of the
plurality of radiating elements to a number of transmission lines.
Clause 18: A method for electronically steering an antenna system, the method comprising:
propagating a surface wave along each of a number of surface wave channels formed
in each of a plurality of radiating elements to form a radiation pattern; coupling
each surface wave channel in the number of surface wave channels formed in each radiating
element in the plurality of radiating elements to a transmission line configured to
carry a radio frequency signal using a surface wave feed in a plurality of surface
wave feeds associated with the plurality of radiating elements; and electronically
steering a main lobe of the radiation pattern by controlling voltages applied to a
plurality of switch elements connecting a plurality of impedance elements in each
of the number of surface wave channels.
Clause 19: The method of clause 18, wherein electronically steering the main lobe
comprises: applying a first level of voltage or a second level of voltage to each
of the plurality of switch elements to create a surface impedance profile for each
surface wave channel of the number of surface wave channels.
Clause 20: The method of clause 18, wherein electronically steering the main lobe
comprises: applying a first level of voltage or a second level of voltage to each
of the plurality of switch elements to modulate between high surface impedance and
low surface impedance.
[0259] The description of the different illustrative embodiments has been presented for
purposes of illustration and description, and is not intended to be exhaustive or
limited to the embodiments in the form disclosed. Many modifications and variations
will be apparent to those of ordinary skill in the art. Further, different illustrative
embodiments may provide different features as compared to other desirable embodiments.
The embodiment or embodiments selected are chosen and described in order to best explain
the principles of the embodiments, the practical application, and to enable others
of ordinary skill in the art to understand the disclosure for various embodiments
with various modifications as are suited to the particular use contemplated.