[0001] This patent application relates to an antenna apparatus. In particular, this patent
application relates to an antenna having polarization diversity.
[0002] The electric field of a propagating electromagnetic wave has two linear components
that are orthogonal to one another. Typically, these components trace out an ellipse
as a function of time. However, the electromagnetic wave might have only a single
electric field component, in which case the electromagnetic wave is said to be linearly
polarized.
[0003] If an electromagnetic wave is linearly polarized, signal quality may be adversely
affected by multipath signals, since many linearly polarized signals with different
polarization might exist at the receiving antenna. A polarization diverse antenna
can be used to improve signal transmission/reception quality in multipath environments
since the signal strength received by such antennas can be greater than with a single
linearly polarized antenna. A polarization diverse antenna can also be used to increase
network capacity since multiple signals of the same frequency, but different polarizations,
can be transmitted from and/or received at a single antenna.
[0004] Conventional linear polarization diversity antennas may have two feed/receive lines
that transmit/receive two respective orthogonal components of the electromagnetic
wave. For example,
Zhang (US 6,593,891) describes a polarization diverse antenna that comprises a dielectric substrate having
an upper conductive surface. A cross-shaped slot is formed in the upper conductive
surface. The lower surface of the dielectric includes elongated conductive strips
that are aligned with the arms of the slot, and a rectangular conductive portion that
is aligned with the centre of the slot. The antenna also includes a pair of feed lines,
each attached to a respective one of the conductive strips.
[0005] Alternately, a linear polarization diversity antenna may have a single feed/receive
line, but have a complex structure to transmit/receive the orthogonal components of
the electromagnetic wave. For instance,
Thudor (US 7,336,233) describes a polarization diverse antenna that comprises five slots that are arranged
in a H-shaped structure on the upper surface of a dielectric substrate. A single feed
line is disposed on the lower surface of the dielectric substrate, and is perpendicular
to the centre slot. The antenna also includes a switching means that are positioned
in the middle of each slot, except the middle slot. Similarly,
Milyakh (US 7,358,916) describes a polarization diverse antenna that comprises four right-angled bent conductive
strips that are disposed on a dielectric substrate. The antenna also includes a switching
network comprising diodes that are formed between the ends of adjacent strips. A single
feed line is connected between the diagonally opposite strips, at the bent portion
thereof.
[0006] A common problem of dual-polarized antenna is the high possibility of crosstalk between
the polarized components.
GENERAL
[0007] In a first aspect, this patent application describes a three-fold polarization diversity
antenna that comprises a slot-loaded patch, and a radiation member that is electromagnetically
coupled to the slot-loaded patch. The radiation member extends through a plane of
the slot-loaded patch.
[0008] In a second aspect, this patent application describes a wireless communications device
that comprises a radio transceiver section, and a three-fold polarization diversity
antenna that is coupled to the radio transceiver section. The three-fold diversity
antenna comprises a slot-loaded patch, and a radiation member that is electromagnetically
coupled to the slot-loaded patch. The radiation member extends through a plane of
the slot-loaded patch.
[0009] The radiation member may be disposed at a substantially right angle to the plane
of the slot-loaded patch. The slot-loaded patch may comprise a pair of intersecting
slots that extend through a planar conductive layer, with the intersecting slots being
disposed at a substantially right angle to each other. The radiation member may terminate
at one end within a central portion of the slot-loaded patch, such that the one end
is physically isolated from the slot-loaded patch.
[0010] In one implementation, the slot-loaded patch comprises a cross-slot-shaped through-hole
that extends through the planar conductive layer. The radiation member comprises a
monopole that extends between a feed point and a centre of the cross-slot-shaped through-hole.
The monopole may comprise a ground plane, and an elongate conductor that extends from
the ground plane and terminates in the centre of the cross-slot-shaped through-hole.
The ground plane may be substantially parallel to the planar conductive layer, with
the elongate conductor being disposed at a substantially right angle to the planar
conductive layer and the ground plane.
[0011] As will become apparent, the three-fold polarization diversity antenna has a simple
compact structure. The antenna also provides good isolation between the polarized
components, and may be used in WLAN networks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Sample embodiments of the three-fold polarization diversity antenna and the wireless
communications device will now be described, with reference to the accompanying drawings,
in which:
Fig. 1 is a schematic diagram depicting certain functional components of the wireless
communications device, including the three-fold polarization diversity antenna;
Fig. 2a is a top perspective view of the three-fold polarization diversity antenna,
depicting the slot-loaded patch, and the radiation member;
Fig. 2b is a side elevation of the three-fold polarization diversity antenna;
Fig. 3 depicts the measured return loss for a WLAN embodiment of the three-fold polarization
diversity antenna;
Fig. 4 depicts the radiation pattern of the three-fold polarization diversity antenna
of Fig. 3; and
Fig. 5 depicts the efficiency of the three-fold polarization diversity antenna of
Fig. 3.
DETAILED DESCRIPTION
[0013] Turning now to Fig. 1, there is shown a wireless communications device 100 that is
configured to operate within a wireless network. Preferably, the communications device
100 is a two-way wireless communications device. Depending on the exact functionality
provided, the wireless communications device 100 may be configured as a wireless base
station, a portable wireless modem, or a wireless data communication device, as examples.
[0014] As shown, the wireless communications device 100 includes a communication subsystem
102, and a data processing system 104 that is coupled to the communication subsystem
102. The communication subsystem 102 performs communication functions, and includes
a wireless transmitter 106, a wireless receiver 108, and an internal antenna 200,
a local oscillator (LOs) 110 and a digital signal processor (DSP) 112 connected to
the transmitter 106 and the receiver 108.
[0015] Preferably, the internal antenna 200 is a wide-band antenna that is configured for
use with one or more of the application bands that are available within the wireless
network. More preferably, the internal antenna 200 is configured for use within a
WLAN (IEEE 802.11x) network. The internal antenna 200 will be discussed in detail
below, with reference to Figs. 2 to 5.
[0016] The data processing system 104 comprises a microprocessor 114, a flash memory 116
and a data port 118. The flash memory 116 includes signal processing instructions
for the DSP 112, and may also include computer processing instructions for the microprocessor
114. The computer processing instructions, when accessed from the flash memory 116
and executed by the microprocessor 114 define an operating system that controls the
overall operation of the communications device 100. Alternately, the data processing
system 104 may also include a volatile memory (RAM) 120. The computer processing instructions
may be copied from the flash memory 116 into the RAM 120, and then accessed from the
RAM 116 and executed by the microprocessor 114.
[0017] The data port 118 interfaces the wireless communications device 100 with a communications
network, such as a wired or wireless local area network (LAN) or wide area network
(WAN). Data packets that are received at the data processing system 104 from the communications
network via the data port 118 are transferred by the operating system to the communication
subsystem 102 for transmission as wireless electromagnetic signals over the wireless
network. Wireless electromagnetic signals to be transmitted over the wireless network
are processed by the DSP 112 and input to the transmitter 106 for digital to analog
conversion, frequency up conversion, and transmission over the wireless network via
the internal antenna 200.
[0018] Conversely, wireless electromagnetic signals that are received by the internal antenna
200 from the wireless network are input to the receiver 108, which performs common
receiver functions such as frequency down conversion, and analog to digital (A/D)
conversion, in preparation for more complex communication functions performed by the
DSP 112. Data packets that are received at the data processing system 104 from the
DSP 112 are transmitted by the operating system over the communications network via
the data port 118.
[0019] Although the communication subsystem 102 is depicting in Fig. 1 having only one transmitter
106 and one receiver 108, the communication subsystem 102 may include additional transmitters
and/or receivers, depending upon the range of frequency bands over which communication
is desired. Similarly, although the communication subsystem 102 is depicted in Fig.
1 with one antenna 200, it should be understood that the wireless communications device
100 may instead comprise two or more of the antennas 200. Further, if the communication
subsystem 102 includes more than one DSP 112, the signals transmitted and received
by the additional transmitter(s)/receiver(s) would preferably be processed by a different
DSP than the transmitter 106 and the receiver 108.
[0020] Figs. 2a and 2b depict the preferred structure of the three-fold polarization diversity
antenna 200. The antenna 200 comprises a slot-loaded patch antenna structure 202,
and a radiation member 204 that is electromagnetically coupled to the patch antenna
structure 202. The patch antenna structure 202 comprises a conductive layer 206, and
a slot-shaped aperture that extends through the conductive layer 206. The conductive
layer 206 typically is substantially planar, and may have a substantially square planar
shape. Alternately, the conductive layer 206 may have rectangular, elliptical or circular
planar shape. Further, the conductive layer 206 need not be planar, but may have an
arcuate shape.
[0021] As shown, the slot-shaped aperture may comprise a pair of elongate linear intersecting
slots 208a, 208b that extend through the conductive layer 206, between the upper and
lower surfaces thereof, thereby forming a cross-slot-shaped through-hole in the conductive
layer 206. Preferably, the intersecting slots 208a, 208b are disposed at a substantially
right angle to each other. However, other orientations of the intersecting slots 208a,
208b may be adopted. For instance, the patch antenna structure 202 may comprise a
single slot; or may comprise three linear intersecting slots oriented 120° with respect
to each other.
[0022] The radiation member 204 extends through a plane of the slot-loaded patch. Preferably,
the radiation member 204 is disposed at a substantially right angle to the plane of
the slot-loaded patch. Further, the radiation member 204 is configured as a grounded
monopole, and comprises a planar ground plane 210, and an elongate conductor 212.
The elongate conductor 212 is physically isolated from the ground plane 210, and extends
from the ground plane 210, terminating proximate the centre portion of the slot-shaped
aperture, between the upper and lower surfaces of the conductive layer 206. With this
configuration, the field distributions produced by the antenna will be symmetric.
Alternately, however, for non-symmetric field distributions, the elongate conductor
212 may terminate at a position that is off-centre. Preferably, the elongate conductor
212 extends vertically upwards through the ground plane 210 towards the slot-shaped
aperture, from a feed point 214 that is disposed below the ground plane 210.
[0023] The antenna 200 may include a dielectric substrate (not shown) that is disposed between
the conductive layer 206 and the ground plane 210. In this implementation, the conductive
layer 206 and the ground plane 210 are disposed on opposite faces of the dielectric
substrate. Further, the dielectric substrate is configured with a through-hole through
which the elongate conductor 212 extends between the ground plane 210 and the conductive
layer 206.
[0024] As shown, the ground plane 210 may be oriented substantially parallel to the planar
conductive layer 206. With this configuration, the elongate conductor 212 is disposed
at a substantially right angle to the planar conductive layer 206 and the ground plane
210. Alternately, however, the planar conductive layer 206 may be inclined relative
to the ground plane 210 at an angle other than a right angle.
[0025] The end of the elongate conductor 212 that is opposite the feed point 214 ("terminal
end") may be disposed within the region 216 of the intersection of the intersecting
slots 208a, 208b, between the upper and lower surfaces of the slot-loaded patch. Alternately,
the terminal end may be disposed above the upper surface of the slot-loaded patch.
The terminal end of the elongate conductor 212 is physically isolated from the slot-loaded
patch. As a result, the radiation member 204 is electromagnetically coupled to the
slot-loaded patch.
[0026] Alternately, the radiation member 204 may be configured as a dipole that is electromagnetically
coupled at the opposite ends thereof to respective patch antenna structures 202. As
in the previous example, the radiation member 204 may comprise an elongate member
whose opposite ends are physically isolated from the slot-loaded patches and terminate
proximate the centre portion of the respective slot-shaped apertures.
[0027] As discussed above, the communication subsystem 102 may be provided with a plurality
of the antennas 200. In a preferred implementation, the conductive layer 206 comprises
a plurality of slot-shaped apertures that are disposed uniformly on a common planar
conductive layer 206. In this variation, the antennas 200 may be disposed uniformly
over the conductive layer 206, thereby providing a planar antenna array. Alternately,
the conductive layer 206 may have a cylindrical configuration, with the plurality
of slot-shaped apertures being disposed uniformly over the cylindrical conductive
layer 206. In this latter variation, preferably each radiation member 204 is disposed
at a substantially right angle to the plane of the associated slot-shaped aperture,
at the centre portion of the associated slot-shaped aperture.
[0028] As is known to persons of skill in the art, the length of a conventional monopole
is one-quarter of the wavelength of the fundamental. However, due to the electromagnetic
coupling between the radiation member 204 and the slot-loaded patch, the length of
the elongate conductor 212 is less than one-quarter of the wavelength (when the radiation
member 204 is configured as a grounded monopole). As a result, the height of the antenna
200 may be less than a conventional monopole antenna having the same minimum resonant
frequency. Further, the antenna 200 does not exhibit the power loss that would otherwise
occur if the radiation member 204 was electrically connected to the slot-loaded patch.
[0029] As is also known to persons of skill in the art, the electric field of a conventional
monopole is polarized in the direction of the monopole. Therefore, the electric field
of the antenna 200 includes a vertically-polarized electric field. However, due to
the electromagnetic coupling between the radiation member 204 and the slot-loaded
patch, the radiation member 204 induces electric currents in the slot-loaded patch.
Since the intersecting slots 208a, 208b of the slot-loaded patch are disposed at a
substantially right angle to each other, the electromagnetic field produced by the
antenna 200 also includes two perpendicular horizontally-polarized electric fields.
As a result, the electromagnetic field produced by the antenna 200 has three orthogonal
polarized electric fields (i.e. three-fold polarization diversity).
[0030] Fig. 3 depicts the measured return loss for one implementation of the antenna 200.
In this implementation, the conductive layer 206 and the ground plane 210 are substantially
square, and the dimensions of the antenna 200 are as follows:
L1 = 75 mm
L2 = 23 mm
L3 = 28 mm
W= 1.5 mm
H = 10 mm
where:
L1 is the length of each side of the ground plane 210;
L2 is the length of each side of the conductive layer 206;
L3 is the length of each of the intersecting slots 208a, 208b;
W is the width of each of the intersecting slots 208a, 208b; and
H is the length of the elongate conductor 212.
[0031] As shown, the frequency range of the antenna 200 covers WLAN IEEE 802.11 b/g (4.9
- 6 GHz).
[0032] Fig. 4 depicts the radiation pattern of the foregoing implementation of the antenna
200, measured at 5.5 GHz. As shown, at this WLAN frequency the electromagnetic field
of the antenna 200 has two perpendicular horizontally-polarized electric fields, with
good isolation between the electric fields.
[0033] Fig. 5 depicts the efficiency of the foregoing implementation of the antenna 200.
As shown, the antenna 200 exhibits good efficiency across the WLAN band, notwithstanding
the multiple polarization diversity of the antenna 200.
1. A three-fold polarization diversity antenna comprising:
a slot-loaded patch comprising a slot extending through a conductive layer; and
a radiation member electromagnetically coupled to the slot-loaded patch, the radiation
member extending through a plane of the slot-loaded patch.
2. The three-fold polarization diversity antenna according to Claim 1, wherein the radiation
member is disposed at a substantially right angle to the plane of the slot-loaded
patch.
3. The three-fold polarization diversity antenna according to Claim 1 or Claim 2, wherein
the slot-loaded patch comprises a pair of intersecting slots extending through a planar
conductive layer, the intersecting slots being disposed at a substantially right angle
to each other.
4. The three-fold polarization diversity antenna according to Claim 1, wherein the radiation
member terminates at one end within a central portion of the slot-loaded patch, the
one end being physically isolated from the slot-loaded patch.
5. The three-fold polarization diversity antenna according to Claim 1, wherein the slot-loaded
patch comprises a cross-slot-shaped through-hole extending through a planar conductive
layer.
6. The three-fold polarization diversity antenna according to Claim 5, wherein the radiation
member comprises a monopole that extends between a feed point and a centre of the
cross-slot-shaped through-hole.
7. The three-fold polarization diversity antenna according to Claim 5, wherein the monopole
comprises a ground plane, and an elongate conductor that extends from the ground plane
and terminates in a centre of the cross-slot-shaped through-hole.
8. The three-fold polarization diversity antenna according to Claim 7, wherein the ground
plane is substantially parallel to the planar conductive layer.
9. The three-fold polarization diversity antenna according to Claim 8, wherein the elongate
conductor is disposed at a substantially right angle to the planar conductive layer
and the ground plane.
10. A wireless communications device comprising:
a radio transceiver section; and
a three-fold polarization diversity antenna according to any one of Claims 1 to 9.
11. The communications device according to Claim 10, configured as a wireless base station.
Amended claims in accordance with Rule 137(2) EPC.
1. A three-fold polarization diversity antenna comprising:
a slot-loaded patch antenna structure comprising a slot extending through a conductive
layer; and
a radiation member electromagnetically coupled to the slot-loaded patch antenna structure,
the radiation member extending through a plane of the slot-loaded patch antenna structure.
2. The three-fold polarization diversity antenna according to Claim 1, wherein the radiation
member is disposed at a substantially right angle to the plane of the slot-loaded
patch antenna structure.
3. The three-fold polarization diversity antenna according to Claim 1 or Claim 2, wherein
the slot-loaded patch antenna structure comprises a pair of intersecting slots extending
through a planar conductive layer, the intersecting slots being disposed at a substantially
right angle to each other.
4. The three-fold polarization diversity antenna according to Claim 1, wherein the radiation
member terminates at one end within a central portion of the slot-loaded patch antenna
structure, the one end being physically isolated from the slot-loaded patch antenna
structure.
5. The three-fold polarization diversity antenna according to Claim 1, wherein the slot-loaded
patch antenna structure comprises a cross-slot-shaped through-hole extending through
a planar conductive layer.
6. The three-fold polarization diversity antenna according to Claim 5, wherein the radiation
member comprises a monopole that extends between a feed point and a centre of the
cross-slot-shaped through-hole.
7. The three-fold polarization diversity antenna according to Claim 5, wherein the monopole
comprises a ground plane, and an elongate conductor that extends from the ground plane
and terminates in a centre of the cross-slot-shaped through-hole.
8. The three-fold polarization diversity antenna according to Claim 7, wherein the ground
plane is substantially parallel to the planar conductive layer.
9. The three-fold polarization diversity antenna according to Claim 8, wherein the elongate
conductor is disposed at a substantially right angle to the planar conductive layer
and the ground plane.
10. A wireless communications device comprising:
a radio transceiver section; and
a three-fold polarization diversity antenna according to any one of Claims 1 to 9.
11. The communications device according to Claim 10, configured as a wireless base station.