FIELD
[0001] The present disclosure relates to a polarisation converter. The present disclosure
also relates to an antenna system for a communications apparatus. The present disclosure
also relates to a vehicle having said antenna system. The present disclosure also
relates to a method of manufacturing a polarisation converter.
BACKGROUND
[0002] Linear-to-circular polarisation converters are known in the art for converting linearly
polarised electromagnetic (EM) radiation to circularly polarised EM radiation.
[0003] One example of a conventional converter comprises a dipole array printed on a grounded
dielectric layer. A linearly polarised EM wave incident on the converter can be converted
to a circularly polarised reflected EM wave.
[0004] However, conventional converters have poor angular stability. That is, the relationship
between axial ratio of the reflected wave (which provides a measure of how circularly
polarised said wave is) and frequency of EM radiation varies considerably depending
on the angle of incidence of the incident linearly polarised radiation. Because of
this, certain frequencies of EM radiation, which are suitably converted to circularly
polarisation at one angle of incidence, are poorly converted at another angle of incidence.
This is problematic, as it is therefore necessary to maintain a consistent angular
relationship between the incident radiation and the converter in order to produce
adequate circularly polarised output. This may be difficult to achieve in practice
and limits widespread application of such converters.
[0005] It is an object of the present invention to provide an improved system and/or method
thereof and/or address one or more of the problems discussed above, or discussed elsewhere,
or to at least provide an alternative system and/or method.
SUMMARY
[0006] According to a first aspect of the present invention there is provided a polarisation
converter comprising: a first element array layer extending in a plane comprising
a first array of spaced apart electrically conductive dipole elements; a second element
array layer extending in a plane comprising a second array of spaced apart electrically
conductive dipole elements; a dielectric layer extending in a plane separating the
first element array layer and the second element array layer, each element array layer
having a first and second axis parallel to the plane of the respective element array
layer, the first axis and second axis being perpendicular axes, wherein one or both
of the element array layers exhibits an anisotropic spatial property. The polarisation
converter may be a linear-to-circular polarisation converter.
[0007] In this way, a device having a double-layer dipole array structure is formed, with
the ability to convert a linearly polarised incident wave to a circularly polarised
reflected wave. Such a converter finds application in converting linearly polarised
radiation from a linear antenna, which are readily available and are low-cost, to
circularly polarised radiation for use in satellite, communication and sensing systems.
[0008] In one example, one or both of the arrays of dipole elements exhibits an anisotropic
spatial property. In one example, the spacing between dipole elements of the array
is different in the first and second axes. In one example, the periodicity of the
array of dipole elements is different in the first and second axes.
[0009] In this way, linear-to-circular polarisation conversion is facilitated. "Anisotropic
spatial property" may mean that a spatial property differs between the first and second
axes, in one or both of the element array layers. Anisotropy is achievable through
periodicity of the element array layers and/or spacing of the dipole elements.
[0010] In one example, one or both of the arrays of dipole elements has a first periodicity
measured along the first axis, and a second periodicity measured along the second
axis, the second periodicity being different to the first periodicity.
[0011] In this way, a polarisation converter having a doubly periodic anisotropic array
structure is formed. Linear-to-circular polarisation of an incident EM wave is facilitated.
[0012] In one example, the first element array layer and second element array layer have
the same first and second periodicity. That is, whilst the first and second periodicity
may be different, the first element array layer may have an array of dipoles having
dipoles spaced according to the first periodicity along the first axis, and spaced
according to the second periodicity along the second axis, and the second element
array layer may have the same arrangement. The first element array layer and second
element array layer may have the same dimensions (i.e. total length and width).
[0013] Advantageously, this tends to lead to a structure in which dipole elements in the
first element array layer have a high element coupling, which improves angular stability.
Moreover, in construction of the converter, array layers having the same periodicity
simplify construction. That is, the array layers may be formed from array layer sheets,
or the array layers may be built up from constituent unit cells, which when assembled
form the element array layers having the same first and second periodicity.
[0014] In one example, the dipole elements of the second element array layer are each located
laterally displaced with respect to the dipole elements of the first element array
layer.
[0015] In this way, a polarisation converter having an anisotropic array structure is formed.
Linear-to-circular polarisation of an incident EM wave is facilitated.
[0016] In one example, the dipole elements of the second element array layer are each located
laterally displaced along the first axis with respect to the dipole elements of the
first element array layer.
[0017] In this way, a polarisation converter having an anisotropic array structure is formed.
Linear-to-circular polarisation of an incident EM wave is facilitated. Nevertheless,
this leads to a construction wherein some overlap between the dipole elements of the
element array layers exists, which tends to provide for high element coupling and
advantageous improvements in angular stability.
[0018] In one example, the dipole elements of the second element array layer are each located
laterally aligned along the second axis with respect to the dipole elements of the
first element array layer.
[0019] In this way, overlap between dipole elements of the element array layers exists,
which tends to provide for high element coupling and advantageous improvements in
angular stability. Some deviation from exact laterally alignment is possible without
loss of angular stability. Nevertheless, this offset is not large enough to produce
overlap along the second axis, as will be understood from the description herein.
[0020] In one example, a plurality of the dipole elements of the first element array layer
and/or second element array layer exhibit an anisotropic spatial property.
[0021] Anisotropy is also realised by the shape or form of the dipole elements. In this
way, a polarisation converter having an anisotropic array structure is formed. Linear-to-circular
polarisation of an incident EM wave is facilitated.
[0022] In one example, each dipole element has a first dimension measured along the first
axis, and a second dimension measured along the second axis, the first and second
dimensions being different.
[0023] The anisotropic spatial property may thereby be defined. Whilst the dipole elements
may be arbitrary in shape, having different first and second dimensions leads to anisotropy,
which facilitates operation as a linear-to-circular polarisation converter.
[0024] In one example, in plan view, a region of one of the dipole elements of the first
element array layer overlaps a region of one or more of the dipole elements of the
second element array layer. In one example, in plan view, a region of one of the dipole
elements of the first element array layer overlaps a region of one or more of the
dipole elements of the second element array layer, along the first axis.
[0025] This provides a construction wherein some overlap between the dipole elements of
the element array layers exists, which tends to provide for high element coupling
and advantageous improvements in angular stability. High element coupling results
in an increase of the effective electric length of the elements, which leads to a
decrease of the array resonant frequency and thereby improves the angular stability
of the polarisation converter. Overlap along the first axis tends to be advantageous
for high element coupling. In some examples, there is no overlap along the second
axis.
[0026] In one example, the end regions of one of the dipole elements of the first element
array layer overlaps an end region of two of the dipole elements of the second element
array layer. Such a construction has been found to be particularly advantageous. The
overlap may be provided by a construction having two element array layers, where one
of the layers is shifted appropriately to provide the described overlap, in plan view.
[0027] In one example, in plan view, between 1 - 50% of the length of one of the dipole
elements of the first element array layer overlaps a region of one or more of the
dipole elements of the second element array layer. In a preferred example, between
20 - 30% of the length of one of the dipole elements of the first element array layer
overlaps a region of one or more of the dipole elements of the second element array
layer. In a highly preferred example, around 26% of the length of one of the dipole
elements of the first element array layer overlaps a region of one or more of the
dipole elements of the second element array layer. The length overlap may be an area
overlap, where appropriate (i.e. there may be a 1 - 50%, 20 - 30% or 26% overlap in
area rather than length).
[0028] It will be understood by the skilled person that, due to the manner in which the
first and second element array layers are arranged, the length or area of overlap,
in plan view, of one of the dipole elements of the first element array layer with
one or more dipole elements of the second element array layer may be the same as the
length or area of overlap, in plan view, of one of the dipole elements of the second
element array layer with one or more dipole elements of the first element array layer.
[0029] In one example, each dipole element has a rectangular cross-sectional profile, for
example a solid rectangle or rectangular loop, or an ovoidal cross-sectional profile,
for example a solid ovoid or an ovoid loop.
[0030] Such exemplary dipole element shapes have been found to be particularly advantageous.
In this way, a polarisation converter having an anisotropic array structure is formed.
Linear-to-circular polarisation of an incident EM wave is facilitated.
[0031] The polarisation converter may comprise a ground plane, wherein the first element
array layer, dielectric layer and second element array layer are disposed above the
ground plane. In one example, the ground plane is a grounded metal substrate. In one
example the ground plane or grounded metal substrate is mounted on, or forms part
of, the polarisation converter or an antenna system comprising the polarisation converter.
This provides for a versatile and self-contained polarisation converter. In another
example, the ground plane or grounded metal substrate is mounted on, or forms part
of, a vehicle to which the polarisation converter is attached. In other words, when
a polarisation converter is attached to the vehicle, it may use part of the vehicle
as a ground plane. In this way, body panels of such vehicles, for example, aircraft
panels or a hull, can be employed and function with the device to convert EM waves
from linear polarisation to circular polarisation. Advantageously, this arrangement
tends to negate the need for conventional exposed antennas on said vehicle, i.e. the
antenna does not extend out with the existing profile of the vehicle, which avoids
drag penalties or low observability penalties, for example, reducing the radar cross
section of the vehicle. Whilst in this example the ground plane is a grounded metal
substrate, this is considered non-limiting and other ground planes may be employed
such as metal alloys, metalloids, metal matrix composites or any other conductive
surface.
[0032] According to a second aspect of the present invention there is provided an antenna
system for a communications apparatus, comprising: an antenna arranged to generate
polarised electromagnetic radiation; and a polarisation converter according to the
first aspect. The antenna may be arranged to generate linearly polarised electromagnetic
radiation. The antenna system may form part of a satellite communications receiver,
such as a GPS, GLONASS or Galileo receiver. In other words, the antenna system may
form part of a navigation system. The antenna system form part of a telecommunications
transceiver, such as a broadband telecommunications transceiver including 4G and 5G.
The antenna system may form part of a tactical datalink receiver, such as a Link-16
or Link-22 receiver.
[0033] In this way, linearly polarised radiation may be generated by an antenna, and converted
to circular polarised radiation. Antennas arranged to generate linearly polarised
EM radiation are readily available and low-cost, especially compared with antenna
arranged to generate circularly polarised radiation. Thus, facilitating the generation
of circularly polarised radiation in this way tends to be highly advantageous.
[0034] According to a third aspect of the present invention there is provided a vehicle
comprising an antenna system according to the second aspect. The vehicle may be an
aircraft, such as a manned or unmanned aircraft. The antenna system may provide a
means for the aircraft to receive communications signals from a base station. Alternatively,
the antenna system may provide means for the aircraft to receive navigation data from
a satellite navigation system. In other words, the vehicle may comprise a navigation
system or communications system comprising the antenna system.
[0035] In this way, advantages in communication and sensing may be realised.
[0036] According to a fourth aspect of the present invention there is provided a method
of converting linearly polarised radiation to circularly polarised radiation comprising:
providing a polarisation converter, communications apparatus, or vehicle according
to the first, second or third aspects respectively; disposing the first element array
layer, dielectric layer and second element array layer above a ground plane; and irradiating
the device with linearly polarised radiation, the reflected radiation being circularly
polarised.
[0037] In one example, the method comprises reflecting linearly polarised radiation from
the polarisation converter, antenna system or vehicle thereby to generate, or transmit,
circularly polarised radiation. In one example, the method comprises mounting a polarisation
converter or antenna system on a vehicle.
[0038] According to a fifth aspect of the present invention there is provided a method of
manufacturing a polarisation converter comprising the steps of: providing a first
element array layer extending in a plane and a second element array layer extending
in a plane, each element array layer having a first and second axis parallel to the
plane of the respective element array layer, the first axis and second axis being
perpendicular axes, wherein one or both of the element array layers exhibit an anisotropic
spatial property; and layering: the first element array layer comprising a first array
of spaced apart electrically conductive dipole elements; the second element array
layer comprising a second array of spaced apart electrically conductive dipole elements;
and a dielectric layer extending in a plane separating the first element array layer
and the second element array layer.
[0039] Features of any of the above aspects may be combined as desired or as appropriate.
BRIEF DESCRIPTION OF THE FIGURES
[0040] Embodiments of the present disclosure will now be described, by way of example only,
with reference to the accompanying drawings in which:
Fig. 1 shows a schematic perspective view of a linear-to-circular polarisation converter
according to the prior art;
Fig. 2 shows a graph of axial ratio of reflected radiation versus frequency, at different
angles of incidence, for the prior art converter of Fig. 1;
Fig. 3 shows a schematic side profile view of a polarisation converter according to
an embodiment;
Fig. 4(a) and (b) show schematic plan views of, in isolation, the first element array
layer and second element array layer of the converter of Fig. 3;
Fig. 5 shows a schematic exploded perspective view of a portion of the converter of
Fig. 3;
Fig. 6(a) and (b) show the geometrical configuration of TM and TE incidence on a portion
of the converter of Fig. 3;
Fig. 7(a) and (b) show graphs of reflection phase for TE and TM components;
Fig. 8(a) and (b) show graphs of axial ratio of reflected radiation versus frequency,
at different angles of incidence;
Fig. 9 shows an antenna system for a communications apparatus;
Fig. 10 shows a vehicle according to an embodiment;
Fig. 11 shows general methodology principles; and
Fig. 12 shows general methodology principles.
DETAILED DESCRIPTION
[0041] Referring to Figure 1, a linear-to-circular polarisation converter 1 according to
the prior art is shown. The polarisation converter 1 comprises an arrangement of dipole
elements 2 arranged in a single layer and printed on a grounded dielectric slab 4.
[0042] The direction of propagation of an incident EM wave (which may be referred to as
the "angle of incidence") is shown at an angle θ measured from the axis normal to
the plane of the layer of dipole elements 2 (the z-axis).
[0043] Referring to Figure 2, axial ratio of reflected radiation versus frequency, at different
angles of incidence, for the converter 1 is shown in graphical representation. The
term "angular stability" is used to refer to the amount of variation of the relationship
between axial ratio and frequency for different angles of incidence of incident EM
waves. As shown in the Figure, the converter 1 has a large variation in the axial
ratio of the reflected radiation at frequencies above around 10 GHz as the angle of
incidence is varied from θ = 0, to θ = 30, to θ = 45. That is, the converter 1 has
poor angular stability at frequencies above around 10 GHz.
[0044] Referring to Figure 3, a polarisation converter 100 according to an embodiment is
shown. More specifically, the polarisation converter is for converting linearly polarised
incident EM radiation into circularly polarised radiation. In another embodiment,
the polarisation converter may be modified to convert circularly polarised incident
radiation into linearly polarised radiation. The converter 100 comprises a first element
array layer 120, and second element array layer 140 and a dielectric layer 160. The
converter 100 further comprises a Taconic RF35 substrate 180. The converter 100 further
comprises a ground plane in the form of a grounded metal substrate 190. The first
element array layer 120, second element array layer 140 and dielectric layer 160 are
disposed above the grounded metal substrate 190. In this exemplary embodiment, an
incident EM wave is reflected from the grounded metal substrate 190, and through interaction
with the first element array layer 120 and second element array layer 140 is converted
from linear-to-circular polarisation. In this example, the grounded metal substrate
190 forms part of the converter 100, although the person skilled in the art will appreciate
that the substrate 190 may be provided separately, and for example may form part of
a structure on which the converter 100 is mounted, for example as part of a ground-based
vehicle, watercraft or aircraft.
[0045] The first element array layer 120 extends in a plane, referred to as a "first plane",
which in this exemplary embodiment is a horizontal plane. The first element array
layer 120 comprises a first array of spaced apart electrically conductive dipole elements
122.
[0046] The second element array layer 140 extends in a plane, referred to as a "second plane",
which in this exemplary embodiment is a horizontal plane. The second element array
layer 140 comprises a second array of spaced apart electrically conductive dipole
elements 142.
[0047] The dielectric layer 160 extends in a plane, referred to as a "third plane", which
in this exemplary embodiment is a horizontal plane. The dielectric layer 160 separates
the first element array layer 120 and the second element array layer 140. That is,
the dielectric layer 160 electrically insulates first element array layer 120 from
the second element array layer 140. The dielectric layer 160 is formed of a polyimide.
[0048] The dipole elements are formed on either side of the dielectric layer 160. In this
exemplary embodiment, the second array of dipole elements 142 are formed above the
substrate 180 and below the dielectric layer 160. The first array of dipole elements
122 are formed above the dielectric layer 160. The dipole elements 122, 142 are formed
of copper. The first element array layer 120, second element array layer 140 and dielectric
layer 160 are substantially parallel.
[0049] Referring to Figures 4(a) and 4(b), element array layers 120, 140 are shown in isolation
and in plan view. As shown in the Figures, each element array layer 120, 140 has a
first and second axis parallel to the plane of the respective element array layer,
the first axis and second axis being perpendicular axes.
[0050] One or both of the element array layers 120, 140 exhibits an anisotropic spatial
property. In this way, linear-to-circular polarisation conversion is facilitated;
the anisotropic design imposes a differential phase shift to the two polarisations
(TM and TE) of the incoming plane wave. By "anisotropic spatial property" it is meant
that a spatial property differs between the first and second axes, in one or both
of the element array layers 120, 140. Anisotropy is achievable through periodicity
of the element array layers 120, 140, spacing of the dipole elements 122, 142, and/or
shape or form of the dipole elements 122, 142.
[0051] The first and second axes are illustrated as "y" and "x" axes in the Figures. As
shown, both of the arrays of dipole elements 122, 142 exhibit an anisotropic spatial
property. That is, in the illustrated embodiment, the spacing between dipole elements
122, 142 is different in the first and second axes. In this way, in one of the axes
the elements in the first element array layer 120 overlap with elements in the second
element array layer 140.
[0052] Additionally, the periodicity of the array of dipole elements is different in the
first and second axes. In this way, there are more dipoles per unit length in the
second axis (the "x" axis) compared to the first axis (the "y" axis). Here, both of
the arrays of dipole elements has a first periodicity measured along the first axis,
and a second periodicity measured along the second axis, the second periodicity being
different to the first periodicity. The first element array layer 120 and second element
array layer 140 have the same first and second periodicity.
[0053] As will be understood from Figures 4(a) and 4(b), in the assembled converter 100
the dipole elements 142 of the second element array layer 140 are each located laterally
displaced with respect to the dipole elements 122 of the first element array layer
120. This may be described as the arrays being "shifted" relative to one another.
Such an arrangement is anisotropic.
[0054] Furthermore, in the assembled converter 100 the dipole elements 142 of the second
element array layer 140 are each located laterally aligned along the second axis with
respect to the dipole elements 122 of the first element array layer 120. This facilitates
element coupling, which will be described in further detail below.
[0055] As mentioned above, anisotropy is also realised by the shape or form of the dipole
elements. In this exemplary embodiment, the dipole elements 122, 142 of the first
element array 120 layer and second element array layer 140 exhibit an anisotropic
spatial property. As shown, each dipole element has a first dimension measured along
the first axis, and a second dimension measured along the second axis. The first and
second dimensions are different. In this illustrated embodiment, each dipole element
122, 142 has a solid rectangular shape. The person skilled in the art will appreciate
that other shapes of dipole elements are suitable and also have a different first
and second dimension, for example rectangular loops, solid ovoids and/or ovoid loops.
[0056] As will be understood from the plan views of the element array layers 120, 140 shown
in Figures 4(a) and 4(b), and also from the portion of the converter 100 illustrated
in Figure 5 shown having a transparent dielectric layer 160, in plan view, a region
of one of the dipole elements 122 of the first element array layer 120 overlaps a
region of one or more of the dipole elements 142 of the second element array layer
140. In this exemplary embodiment, in plan view, one of the dipole elements 122 of
the first element array layer 120 overlaps an end region of two of the dipole elements
142 of the second element array layer 140. This overlap provides a strong capacitive
coupling of the elements between the layers 120, 140. This leads to improvements in
angular stability of the converter 100, which will be described in further detail
below. In this exemplary embodiment, there is a total overlap (i.e. including both
overlapping ends) of around 26% of the length of the dipole element.
[0057] Dimensions of a converter 100 according to an exemplary embodiment are provided with
reference to Figures 3, 4(a), 4(b) and 5. In the exemplary embodiment described herein,
which is the exemplary embodiment to which the graphs of Figures 7 and 8 relate, the
converter 100 has the following dimensions: A (height of the layers 120, 140, 160)
= 0.12mm; B (height of the substrate 180) = 1.524mm; L (length of a dipole element)
= 2.15mm; W (width of a dipole element) = 0.5mm; Dx (width of a "unit cell" of the
element array layer 120, 140) = 1mm; Dy (length of a "unit cell" of the element array
layer 120, 140) = 3.75mm; Dy
l2 (shifting of dipole elements 142 of the second element array layer 140 with respect
to the dipole elements 122 of the first element array layer along the y axis, when
viewed in plan view) = 1.875mm; dipole element length overlap at one end region =
0.275mm.
[0058] The dimensions of the exemplary embodiment are provided without limitation or loss
of generality of the structure of the converter 100. The person skilled in the art
will appreciate that variations of the dimensions are possible whilst still functioning
as a linear-to-circular polarisation converter.
[0059] Referring to Figures 6(a) and 6(b), the geometrical configuration of an incident
EM wave with the converter 100 is shown, with only a portion of the converter 100
being shown in the Figures. The direction of propagation of a linearly polarised incident
EM wave (which may be referred to as the "angle of incidence") is shown at an angle
θ measured from the axis normal to the planes of the element array layers 120, 140
and dielectric layer 160. Figures 6(a) and 6(b) illustrate the TM and TE components
respectively of the linearly polarised incident wave, with equal magnitude and phase
for θ = 0. The E-field, then, lies at an angle of 45° or 135° to the y-axis. The incident
wave has an electric field component E, a magnetic field component H, and a wave vector
k.
[0060] Referring to Figures 7(a) and 7(b), graphs of reflection phase for TE (solid lines)
and TM (dashed lines) components versus frequency are shown. Figures 7(a) and 7(b)
illustrate the reflection phase versus frequency in two mutually orthogonal planes
of incidence; Figure 7(a) shows the x-z plane or Φ = 0°, and Figure 7(b) shows the
y-z plane or Φ = 90°. In order for the converter 100 to convert a linearly polarised
incident wave to a circularly polarised reflected wave, the converter 100 should generate
a phase difference of odd multiples of 90° to the incident wave. In Figures 7(a) and
7(b), the reflection phase is shown when the linearly polarised wave is incident at
an angle of θ = 45° to the y-axis. As can be determined from the graphs, linear-to-circular
polarisation is achieved at various of frequencies, where the reflection phase is
equal to 270°.
[0061] Referring to Figures 8(a) and 8(b), axial ratio of reflected radiation versus frequency,
at different angles of incidence, for the converter 100 is shown in graphical representation.
As mentioned above, the term "angular stability" is used to refer to the amount of
variation of the relationship between axial ratio and frequency for different angles
of incidence of incident EM waves.
[0062] Figures 8(a) and 8(b) illustrate the axial ratio versus frequency in two mutually
orthogonal planes of incidence; Figure 8(a) shows the x-z plane or Φ = 0°, and Figure
8(b) shows the y-z plane or Φ = 90°. As can be established from the figure, the converter
100 has a reduced variation in the axial ratio of the reflected radiation, when compared
with the graph of Figure 2 which relates to the conventional converter 1, at frequencies
above 10GHz as the angle of incidence is varied in the same manner from θ = 0 (solid
line), to θ = 30 (dotted line), to θ = 45 (dashed line). That is, the converter 100
has improved angular stability at frequencies above around 10 GHz.
[0063] The high element coupling, due to the above described arrangement of element array
layers and dipole elements, leads to the improvements in angular stability demonstrated
herein. Element coupling provides an increase of the effect element. This results
in a change of the array resonant frequency. From the Figures, it is understood that
the circular polarisation performance in terms of axial ratio, angular stability and
3-dB-axial ratio bandwidth is satisfactory for the frequency range between 8.2 - 18.3
GHz for both TE and TM in X band and KU band. This frequency range is obtained using
a converter 100 having the dimensions (i.e. dipole element dimensions, layer heights
etc.) as described above.
[0064] The person skilled in the art will appreciate that other dimensions are possible
whilst still maintaining angular stability, but the frequency range may be different
where converter dimensions are changed. For example, a larger (or longer) dipole will
have the effect of shifting the frequency range to lower frequencies, as it will couple
to incident fields of longer wavelengths. Furthermore, increasing the overlap of the
dipoles has the effect of increasing the capacitive coupling of the elements between
the layer 120, 140. This will, in turn, shift the frequency range to lower frequencies.
The choice of substrate 180 also affects the operative frequency range. A substrate
material with a high relative permittivity will have the effect of decreasing the
effective wavelength of the incoming field. This means that the dipoles appear "electrically
longer" and therefore the operative frequency range of the converter 100 will be shifted
lower.
[0065] It will be understood by the person skilled in the art that the structure of the
converter 100 tends to reduce the effects of grating lobes, which are undesirable
features in antenna design. The grating lobes are pushed to higher frequencies due
to the design of the converter 100, in particular the change in the resonant frequency
due to the high element coupling, leading to benefits in angular stability. Sensitivity
to the angle of incidence of incident EM radiation thereby tends to be reduced.
[0066] Referring to Figure 9, an antenna system 1000 is shown. The antenna system 1000 comprises
an antenna 1100 arranged to generate linearly polarised EM radiation. Such antennas
are well known in the art, but may include a whip antenna, stripline antenna, monopole
antenna, dipole antenna, patch antenna. The antenna system 1000 may form part of a
communications apparatus for providing a communications link with another communications
apparatus, where that link operates according to a standard such as GSM, CDMA, LTE,
WiMax, future 5G standards or the like within the 698-3600MHz spectrum region. The
antenna system 1000 may be coupled to a transceiver, transmitter or receiver, power
source and other standard components to enable a communications link. The receiver
may be a satellite navigation receiver, such as for receiving navigation data from
GPS, GLONASS or Galileo systems. In other words, the antenna system 1000 may form
part of a navigation system.
[0067] The antenna system 1000 further comprises a polarisation converter 100 according
to an embodiment
[0068] Referring to Figure 10, a vehicle, for example a ground-based vehicle, aircraft,
watercraft, spacecraft or satellite 2000 is shown. The vehicle 2000 comprises a polarisation
converter 100. The vehicle 2000 may comprise a antenna system 1000 as described with
reference to Figure 9. In other words, the vehicle may comprise a navigation system
having the antenna system 1000.
[0069] Referring to Figure 11, methodology principles according to an embodiment are shown.
The method is a method of converting linearly polarised radiation to circularly polarised
radiation. Step 3000 comprises providing a polarisation converter 100, antenna system
1000 or vehicle 2000, for example a ground-based vehicle, aircraft or watercraft,
according to an embodiment. Step 3200 comprises disposing the first element array
layer, dielectric layer and second element array layer above a ground plane. The ground
plane acts as a reflective surface from which the wave is reflected. Step 3400 comprises
irradiating the device with linearly polarised radiation, the reflected radiation
being circularly polarised. Interaction with the element array layers, and in particular
as a result of their anisotropic property, causes linear-to-circular polarisation
conversion.
[0070] Referring to Figure 12, methodology principles according to an embodiment are shown.
The method is a method of manufacturing a linear-to-circular polarisation converter
100. Step 4000 comprises providing a first element array layer extending in a plane
and a second element array layer extending in a plane, each element array layer having
a first and second axis parallel to the plane of the respective element array layer,
the first axis and second axis being perpendicular axes, wherein one or both of the
element array layers exhibit an anisotropic spatial property. Step 4200 comprises
layering: the first element array layer comprising a first array of spaced apart electrically
conductive dipole elements; the second element array layer comprising a second array
of spaced apart electrically conductive dipole elements; and a dielectric layer extending
in a plane separating the first element array layer and the second element array layer.
[0071] Polarisation converters 100 as described above find application, and advantage, in
satellite, communication, navigation and sensing systems. For example, in satellite
applications, such converters can be used to minimise the effect of Faraday rotation
caused by the ionosphere. Further advantages are found in multipath propagation and
rain clutter suppression.
[0072] At least some of the example embodiments described herein may be constructed, partially
or wholly, using dedicated special-purpose hardware. Terms such as 'component', used
herein may include, but are not limited to, a hardware device, such as circuitry in
the form of discrete or integrated components, a Field Programmable Gate Array (FPGA)
or Application Specific
[0073] Integrated Circuit (ASIC), which performs certain tasks or provides the associated
functionality. Various combinations of optional features have been described herein,
and it will be appreciated that described features may be combined in any suitable
combination. In particular, the features of any one example embodiment may be combined
with features of any other embodiment, as appropriate, except where such combinations
are mutually exclusive.
[0074] Throughout this specification, the term "comprising" or "comprises" means including
the component(s) specified but not to the exclusion of the presence of
others.
1. A polarisation converter (100), comprising:
a first element array layer (120) extending in a plane comprising a first array of
spaced apart electrically conductive dipole elements (122);
a second element array layer (140) extending in a plane comprising a second array
of spaced apart electrically conductive dipole elements (142);
a dielectric layer (160) extending in a plane separating the first element array layer
(120) and the second element array layer (140),
each element array layer (120, 140) having a first and second axis parallel to the
plane of the respective element array layer, the first axis and second axis being
perpendicular axes,
wherein one or both of the element array layers (120, 140) exhibits an anisotropic
spatial property.
2. The polarisation converter (100) as claimed in claim 1, wherein one or both of the
arrays of dipole elements (122, 142) exhibits an anisotropic spatial property.
3. The linear-to-circular polarisation converter (100) as claimed in claim 2, wherein
one or both of the arrays of dipole elements (122, 142) has a first periodicity measured
along the first axis and a second periodicity measured along the second axis, the
second periodicity being different to the first periodicity.
4. The polarisation converter(100) as claimed in claim 3, wherein the first element array
layer (120) and second element array layer (140) have the same first and second periodicity.
5. The polarisation converter(100) as claimed in any previous claim, wherein the dipole
elements of the second element array layer (142) are each located laterally displaced
with respect to the dipole elements of the first element array layer (122).
6. The polarisation converter as claimed in claim 5, wherein the dipole elements of the
second element array layer are each located laterally displaced along the first axis
with respect to the dipole elements of the first element array layer
7. The polarisation converter (100) as claimed in claim 6, wherein the dipole elements
of the second element array layer (142) are each located laterally aligned along the
second axis with respect to the dipole elements of the first element array layer (122).
8. The polarisation converter (100) as claimed in any previous claim, wherein a plurality
of the dipole elements of the first element array layer (122) and/or second element
array layer (142) exhibit an anisotropic spatial property.
9. The polarisation converter (100) as claimed in claim 8, wherein each dipole element
has a first dimension measured along the first axis, and a second dimension measured
along the second axis, the first and second dimensions being different.
10. The polarisation converter (100) as claimed in any previous claim wherein, in plan
view, a region of one of the dipole elements of the first element array layer (120)
overlaps a region of one or more of the dipole elements of the second element array
layer (140).
11. The polarisation converter (100) as claimed in claim 10, wherein, in plan view, between
20 - 30% of the length of one of the dipole elements of the first element array layer
(120) overlaps a region of one or more of the dipole elements of the second element
array layer (140).
12. The polarisation converter (100) as claimed in any previous claim, comprising a ground
plane (190), wherein the first element array layer (120), dielectric layer (160) and
second element array layer (140) are disposed above the ground plane (190).
13. An antenna system (1000) for a communications apparatus, comprising:
an antenna (1100) arranged to generate linearly polarised electromagnetic radiation;
and
a linear-to-circular polarisation converter (100) as claimed in any previous claim.
14. A vehicle (2000) comprising the antenna system (1000) according to claim 13.
15. A method of manufacturing a polarisation converter, comprising the steps of:
providing a first element array layer (120) extending in a plane and a second element
array layer (140) extending in a plane, each element array layer having a first and
second axis parallel to the plane of the respective element array layer, the first
axis and second axis being perpendicular axes, wherein one or both of the element
array layers (120, 140) exhibit an anisotropic spatial property; and
layering:
the first element array layer (120) comprising a first array of spaced apart electrically
conductive dipole elements (122);
the second element array layer (140) comprising a second array of spaced apart electrically
conductive dipole elements (142); and
a dielectric layer (160) extending in a plane separating the first element array layer
(120) and the second element array layer (140).