EP2477275A1

EP2477275A1 - Patch antenna

Info

Publication number: EP2477275A1
Application number: EP11360006A
Authority: EP
Inventors: Titos Kokkinos
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2011-01-12
Filing date: 2011-01-12
Publication date: 2012-07-18

Abstract

A compact patch antenna for use in an antenna array in a wireless telecommunications network. The patch antenna is operable to receive a feed signal and transform that feed signal to a radiated output signal. The compact patch antenna comprises: a ground plate and a radiating element operable to radiate the output signal. The radiating element is located substantially parallel to, and spaced from, the ground plate. The antenna further comprises a capacitive loading element extending from the ground plate. The loading element is arranged to define a cavity between the radiating element and the ground plate, and is spaced from the radiating element to define a predetermined capacitive gap between the radiating element and the capacitive loading element. The predetermined capacitive gap is selected to alter capacitance of the cavity. The antenna also comprises a differential signal feed mechanism operable to couple the feed signal to the radiating element, and alter inductance of the cavity in a predetermined manner selected to substantially compensate for a reduction in output signal bandwidth caused by the alteration to the cavity capacitance caused by the predetermined capacitive gap.

Description

FIELD OF THE INVENTION

The present invention relates to a compact patch antenna.

BACKGROUND

In a typical wireless telecommunications system, user equipment roam through the wireless telecommunications system. Base stations are provided which support areas of radio coverage. A number of such base stations are provided and are distributed geographically in order to provide a wide area of coverage to user equipment. When user equipment is within an area served by a base station, communications may be established between the user equipment and the base station over associated radio links. Each base station typically supports a number of sectors within the geographical area of service.
Typically a different antenna, or antenna array within a base station supports each associated sector. Accordingly, each base station has multiple antennas or antenna arrays and signals sent through the different antennas are arranged to provide a sectorised approach.
With the introduction of 4G cellular systems, the beam scanning requirements from antenna panels are significantly extended: larger beam scanning ranges are required in the elevation, and some applications have beam scanning requirements in the azimuth, for example, low-power small-cell base-stations for improving indoors/urban coverage and/or capacity.
Aspects described herein offer an antenna having properties which addresses some issues with known antenna architectures.

SUMMARY

Accordingly, a first aspect provides a compact patch antenna for use in an antenna array in a wireless telecommunications network, the patch antenna being operable to receive a feed signal and transform the feed signal to a radiated output signal, the compact patch antenna comprising:

a ground plate;
a radiating element operable to radiate the output signal, the radiating element located substantially parallel to, and spaced from, the ground plate;
a capacitive loading element extending from the ground plate and arranged to define a cavity between the radiating element and the ground plate, the capacitive loading element being spaced from the radiating element to define a predetermined capacitive gap between the radiating element and the capacitive loading element, the predetermined capacitive gap being selected to alter capacitance of the cavity; and
a differential signal feed mechanism operable to couple the feed signal to the radiating element, and alter inductance of the cavity in a predetermined manner selected to substantially compensate for a reduction in output signal bandwidth caused by the alteration to the cavity capacitance caused by the predetermined capacitive gap.

Typical antenna arrays or panels used in modern cellular wireless telecommunications systems are 1-D, high-gain arrays employed to provide coverage across large cells, known as macro cells. Such antenna arrays typically provide a main radiating beam having an azimuth beamwidth of around 65° to 90° and an elevation beamwidth of 5° to 20°. In most deployment scenarios, the beam itself is usually slightly downtilted off the broadside direction. The beam scanning requirements from such arrays are typically limited; a reconfigurable 0° to 15° downtilt is usually required in the elevation plane to accurately define the radius of the cells depending upon the antenna position and the served traffic.
Such typical antenna arrays typically comprise high-gain (7 to 9 dBi) broadside radiators, placed adequately apart (approximately 0.8λ) to provide large array gain values for any of the required off-broadside radiating directions (0 ° to 15 ° off broadside).
The first aspect recognizes that with the introduction of 4G cellular systems, the beam scanning requirements from antenna panels are significantly extended: larger beam scanning ranges are required in the elevation, and some applications have beam scanning requirements in the azimuth, for example, low-power small-cell base-stations for improving indoors/urban coverage and/or capacity. Especially in the latter cases, reconfigurable beam tilts of the order of even ±45° off broadside may be required. For such low-power applications these applications, the array gain may not be as critical to overall array design as side-lobe levels (SLL) or grating lobe levels (GLL) of the array over the whole azimuthal beam-scanning range, since the SLL and/or GLL may be the major factor determining interference experienced by user equipment connected to adjacent base-stations.
The feasibility of such beam scanning properties requires an evolution of typical antenna panels in two major directions. First, the feeding networks of such antenna arrays may require a redesign to meet such new, much tougher to implement, requirements. Second, the high-gain, sparsely spaced radiators of typical high-power panels may be substituted by arrays able to exhibit sufficient gain and bandwidth properties, able to form compact arrays (array period < 0.5λ) which achieve large beam-scanning ranges with reduced SLL and GLL.
On the first front, the deployment of Active Antenna Arrays (AAA) in cellular systems may provide a niche solution to the difficulties associated with the design of complicated passive feeding networks, namely significant losses and difficulties in achieving required accuracy. In the context of AAA, each element of an array is accompanied by its own transceiver that can actively set and adjust the magnitude and phase of the RF signal transmitted by this antenna element.
On the second front, the first aspect provides a compact antenna design suitable for use in low-power arrays meeting the beam scanning requirements of the aforementioned applications.
The first aspect provides patch antenna designs that incorporate an alternative mechanism to achieve antenna miniaturization (footprint reduction). Embodiments offer variable miniaturization factors, which are achieved by introducing vertical walls around the patch and in close proximity with the radiating edges. These walls, that effectively form a cavity around the patch (cavity-backed patch), capacitively load the patch enabling the reduction of its resonance frequency for a given physical length. Specifically, the shorter the distance between the radiating edges of the patch and the loading walls, the greater the supported capacitance is and consequently larger miniaturization factors can be achieved.
In one embodiment, the capacitive loading element comprises a wall surrounding said radiating element. Provision of loading surrounding walls serves as a convenient manner to form a capacitive gap and also provides good isolation between adjacent cavity-backed patches by suppressing both guided (surface waves) and unguided modes (radiation coupling) supported between adjacent antenna elements in an antenna array.
In one embodiment, the predetermined capacitive gap is defined between an edge of the radiating element and a substantially planar surface of the capacitive loading element. Accordingly, the capacitive loading element may be vertically aligned around the radiating element. The capacitive gap may be defined between radiating edges of the radiating element and the loading element.
In one embodiment, the predetermined capacitive gap is defined between a portion of a substantially planar surface of the radiating element and a substantially planar surface of the capacitive loading element. Accordingly, by allowing the loading walls not only to be vertically aligned around the patch, but also to extend horizontally above the patch, an overlapping area between radiating element and loading element can be increased and the loading capacitance may be increased, thereby allowing a greater antenna miniaturisation factor to be achieved.
In one embodiment, a dielectric material is located in the predetermined capacitive gap. Accordingly, by providing a dielectric material, appropriately chosen, in the gap, the resulting capacitance can be altered. By appropriate dielectric choice, an increase of loading capacitance can be achieved and hence a greater miniaturisation.
In one embodiment, the radiating element and the capacitive loading element have a substantially identical shape in cross-section. It will be appreciated that in the general case, the cross-section of a radiating element of a patch antenna in accordance embodiments described herein may take any appropriate shape, including, for example, rectangular, polygonal, circular and similar, and that any appropriately shaped loading element, including a loading wall can be chosen, and that the cross sectional shape of the loading element need not be identical to that of the radiating element, provided that the resulting capacitive gap is selected to achieve the desired alteration in capacitance. In general, the surrounding wall does not have to be identical with the shape of the radiating patch; it can be of any shape, provided that there are parts of the circumference of the patch that are in close proximity to the wall.
In one embodiment, the differential signal feed mechanism comprises a pair of inductive feed posts. In one embodiment, the inductive feed posts comprise posts which increase in cross sectional area along their length. In one embodiment, the inductive feed posts are stepped in cross sectional area. Accordingly, use of a differential feed mechanism allows for fine control a feed signal fed to the radiating element, and allows for control of resulting impedance of the antenna. The exact shape, thickness, and position of these probes have can be properly optimized separately for each feed signal, such that their total inductance is chosen to match a loading capacitance provided by the loading element.
In one embodiment, the feed signal has a wavelength of around λ and the compact patch antenna has a footprint of substantially (0.5λ)². Such antennas offer advantageous properties when placed in an antenna array. In some embodiments, the targeted footprint is less than (0.5λ)², or significantly less.
In one embodiment, the radiating element comprises a dual polarized radiating element, operable to receive two orthogonal input signals and radiate two orthogonal output signals, the capacitive loading element being spaced from the radiating element to define a predetermined capacitive gap for each of the orthogonal signals. Each of the two signal polarizations can be tuned separately by separately optimising and properly setting a distance between the loading walls and the corresponding radiating element.
In one embodiment, the compact patch antenna is formed from metallised plastic. Accordingly, such antennas can be manufactured in a low-cost and fully automated fabrication process. The antennas can comprise 3-D forms made of metalized plastic and may be mounted on PCBs.
A second aspect provides a method of forming a compact patch antenna for use in an antenna array in a wireless telecommunications network, the patch antenna being operable to receive a feed signal and transform the feed signal to a radiated output signal, the method comprising:

providing a ground plate;
providing a radiating element operable to radiate the output signal, and locati ng the radiating element substantially parallel to, and spaced from, the ground plate; arranging a capacitive loading element extending from the ground plate to define a cavity between the radiating element and the ground plate, the capacitive loading element being spaced from the radiating element to define a predetermined capacitive gap between the radiating element and the capacitive loading element, the predetermined capacitive gap being selected to alter capacitance of the cavity; and
providing a differential signal feed mechanism operable to couple the feed signal to the radiating element, and alter inductance of the cavity in a predetermined manner selected to substantially compensate for a reduction in output signal bandwidth
caused by the alteration to the cavity capacitance caused by the predetermined capacitive gap.

In one embodiment, the capacitive loading element comprises a wall arranged to surround the radiating element.
In one embodiment, the predetermined capacitive gap is defined between an edge of the radiating element and a substantially planar surface of the capacitive loading element.
In one embodiment, the predetermined capacitive gap is defined between a portion of a substantially planar surface of the radiating element and a substantially planar surface of the capacitive loading element.
In one embodiment, the method further comprises the step of locating a dielectric material in the predetermined capacitive gap.
In one embodiment, the radiating element and capacitive loading element are arranged to have a substantially identical shape in cross-section.
In one embodiment, the differential signal feed mechanism comprises a pair of inductive feed posts.
In one embodiment, the inductive feed posts are arrange to increase in cross sectional area along their length.
In one embodiment, the inductive feed posts are stepped in cross sectional area.
In one embodiment, the feed signal has a wavelength of around λ and the compact patch antenna is arranged to have a footprint of substantially (0.5λ)².
In one embodiment, the radiating element comprises a dual polarized radiating element, operable to receive two orthogonal input signals and radiate two orthogonal output signals, the capacitive loading element is arranged to be spaced from the radiating element to define a predetermined capacitive gap for each of the orthogonal signals.
In one embodiment, the method further comprises the step of forming components of the antenna from metallised plastic.
Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings in which:

Figure 1 illustrates schematically a cross sectional side view of an antenna according to one embodiment;
Figure 2 illustrates schematically a top view of an antenna according to one embodiment;
Figure 3 illustrates schematically in cross-section, an antenna according to one embodiment;
Figure 4 illustrates a model in three dimensions of an antenna according to one embodiment;
Figure 5 is a rear view of the antenna of Figure 4;
Figure 6 shows the simulated S-parameters of the antenna shown in Figures 4 and 5;
Figure 7 illustrates a 1 x4 antenna array according to one embodiment;
Figure 8 illustrates simulated S-parameters of the array elements of Figure 7;
Figure 9 illustrates the radiation pattern of the 1 x4 array of Figure 7 for the case that the beam is scanned at 30°;
Figure 10 shows a 3-D model of a proposed antenna according to one embodiment;
Figure 11 is a rear view of the antenna of Figure 10;
Figure 12 illustrates simulated S-parameters of the antenna of Figures 10 and 11;
Figure 13 shows a 2 x 3 antenna array according to one embodiment; and
Figure 14 shows the simulated S-parameters of an antenna element located in the array of Figure 13.

DESCRIPTION OF THE EMBODIMENTS

In a typical wireless telecommunications system, user equipment roam through the wireless telecommunications system. Base stations are provided which support areas of radio coverage. A number of such base stations are provided and are distributed geographically in order to provide a wide area of coverage to user equipment. When user equipment is within an area served by a base station, communications may be established between the user equipment and the base station over associated radio links. Each base station typically supports a number of sectors within the geographical area of service.
Typically a different antenna, or antenna array within a base station supports each associated sector. Accordingly, each base station has multiple antennas or antenna arrays and signals sent through the different antennas to provide a sectorised approach.
Typical antenna arrays or panels used in modern cellular wireless telecommunications systems are 1-D, high-gain arrays employed to provide coverage across large cells, known as macro cells. Such antenna arrays typically provide a main radiating beam having an azimuth beamwidth of around 65° to 90° and an elevation beamwidth of 5° to 20°. In most deployment scenarios, the beam itself is usually slightly downtilted off the broadside direction. The beam scanning requirements from such arrays are typically limited; a reconfigurable 0° to 15° downtilt is usually required in the elevation plane to accurately define the radius of the cells depending upon the antenna position and the served traffic.
Such typical antenna arrays typically comprise high-gain (7 to 9 dBi) broadside radiators, placed adequately apart (approximately 0.8λ) to provide large array gain values for any of the required off-broadside radiating directions (0° to 15° off broadside).
With the introduction of 4G cellular systems, the beam scanning requirements from antenna panels are significantly extended: larger beam scanning ranges are required in the elevation, and some applications have beam scanning requirements in the azimuth, for example, low-power small-cell base-stations for improving indoors/urban coverage and/or capacity. Especially in the latter cases, reconfigurable beam tilts of the order of even ±45° off broadside may be required. For such low-power applications these applications, the array gain may not be as critical to overall array design as side-lobe levels (SLL) or grating lobe levels (GLL) of the array over the whole azimuthal beam-scanning range, since the SLL and/or GLL may be the major factor determining interference experienced by user equipment connected to adjacent base-stations.
The feasibility of such beam scanning properties requires an evolution of typical antenna panels in two major directions. First, the feeding networks of such antenna arrays may require a redesign to meet such new, much tougher to implement, requirements. Second, the high-gain, sparsely spaced radiators of typical high-power panels may be substituted by arrays able to exhibit sufficient gain and bandwidth properties, able to form compact arrays (array period < 0.5λ) which achieve large beam-scanning ranges with reduced SLL and GLL.
On the first front, the deployment of Active Antenna Arrays (AAA) in cellular systems may provide a niche solution to the difficulties associated with the design of complicated passive feeding networks, namely significant losses and difficulties in achieving required accuracy. !n the context of AAA, each element of an array is accompanied by its own transceiver that can actively set and adjust the magnitude and phase of the RF signal transmitted by this antenna element.
On the second front, compact antenna design suitable for use in low-power arrays meeting the beam scanning requirements of the aforementioned applications are described herein.
The majority of the radiators used in high-power cellular base-stations are cross-polarized dipole-based elements fed against ground planes, also known as reflectors. One advantage of such radiator elements is that they can be designed to be sufficiently broadband (FBW > 50%), supporting multiple frequency bands and communication standards. Such radiators usually have a footprint around (0.5λ)² and a profile of the order of 0.5λ in the middle of their operating band. Such radiators exhibit good co-pol isolation (isolation between the co-polarized elements of two adjacent radiators) and cross-pol isolation (isolation between the two cross-polarized elements of the same radiator) under the assumption of large separation between adjacent elements (typically 0.7λ at the lower part of the operating bandwidth). However, the performance of such radiator elements significantly deteriorates as the separation between two adjacent radiators decreases (for example, at 0.5λ and below). In such cases both the co-pol and cross-pol couplings increase and the antenna detunes. Therefore such antenna elements are not suitable for the compact antenna arrays of 4G deployments where large beam scanning ranges may be required.
Another class of antennas that is a candidate for compact antenna arrays for 4G base-stations is patch antennas. The footprint of a typical air-filled patch antenna is approximately (0.5λ)². Therefore, in order to be used in compact antenna arrays (arrays having an array period of less than 0.5λ), the footprint of the patch cavity can be decreased through some kind of loading. The most conventional way of loading patches can be achieved by filling of a cavity of such a patch antenna with a dielectric material, which serves to increase the electrical length that corresponds to a given physical length. However, loading patches with dielectric materials inherently decreases the antennas operating bandwidth, decreases the overall radiation efficiency, generates surfaces waves that increase the coupling between adjacent patches and imposes limitations on the height of the resonant cavities.
Embodiments described herein relate to patch antenna designs that incorporate an alternative mechanism to achieve antenna miniaturization (footprint reduction). Embodiments offer variable miniaturization factors, which are achieved by introducing vertical walls around the patch and in close proximity with the radiating edges. These walls, that effectively form a cavity around the patch (cavity-backed patch), capacitively load the patch enabling the reduction of its resonance frequency for a given physical length. Specifically, the shorter the distance between the radiating edges of the patch and the loading walls, the greater the supported capacitance is and consequently larger miniaturization factors are achieved.
In some embodiments, by feeding the antennas differentially though a pair of inductive posts, a satisfactory control of input impedance for a large range of the patch heights can be achieved, allowing a matching of a reduced footprint antenna over fractional bandwidths ranging from 3% to 20%.
Provision of loading surrounding walls also provides good isolation between adjacent cavity-backed patches by suppressing both guided (surface waves) and unguided modes (radiation coupling) supported between adjacent antenna elements.
Such features make the proposed antenna embodiments suitable for use in low-power compact antenna arrays.
Figure 1 illustrates schematically a cross sectional side view of an antenna according to one embodiment. The antenna of Figure 1 is a differentially fed, cavity-backed patch antenna. As shown in Figure 1, a radiating patch 10 is fed through probe pairs 11. The exact shape and dimensions of the inductive probe pairs assist in ensuring impedance matching of components of the antenna.
The patch antenna of Figure 1 is provided with surrounding walls 12, placed in close proximity to the radiating patch 10. Surrounding walls 12 operate to loading the radiating patch 10 through capacitive gaps 13.
Figure 2 illustrates schematically a top view of an antenna according to one embodiment. The patch antenna 20 illustrated in Figure 2 is substantially square in cross-section. It will be appreciated that in the general case, the cross-section of a patch antenna in accordance embodiments described herein may take any appropriate shape, including, for example, rectangular, polygonal, circular etc. In the embodiment shown in Figure 2, a surrounding wall 21 is provided, that surrounding wall 21 having the same geometrical shape, in this case, square, as the patch antenna 20. It will be appreciated that in the general case, the surrounding wall can take any appropriate shape either identical or not to the patch.
In the antenna illustrated in Figure 2, two pairs of feeding probes 22, 23 are provided. Each of these pairs is feeding an orthogonal signal polarization, resulting in a dual-polarized antenna. Each of the two signal polarizations can be tuned separately by separately optimising and properly setting a distance between loading walls and the corresponding radiating patches. For example, the exact resonant frequency of the horizontal polarization of the antenna illustrated in Figure 2 is tuned by properly tuning an appropriate pair of capacitive gaps 24 provided between the patch 20 and the surrounding wall 21, whilst the vertical polarization is set by properly setting a pair of gaps 25 provided between the patch 20 and the surrounding wall 21.
Embodiments shown in Figure 1 and Figure 2 may exhibit some limitations regarding footprint miniaturization factors that can be achieved, given that the range of the capacitance provided by simple gaps 13, 24 and 25 is also limited.
In some embodiments, such a limitation may be overcome by allowing the loading walls not only to be vertically aligned around the patch, but also to extend horizontally above the patch.
Figure 3 illustrates schematically in cross-section, an antenna according to one embodiment. In the antenna shown in Figure 3, an overlapping area between a patch and loading wall 31 is increased by arranging the loading wall in such a manner that it extends horizontally above the patch. The loading capacitance is accordingly increased, allowing for significantly larger miniaturization factors. In some embodiments, in order to secure a constant capacitive gap between the horizontal part of loading wall 31 and the patch, a dielectric layer 32 may be inserted therebetween. Depending on the dielectric properties of this material, a further increase of the loading capacitance, and hence the miniaturization factor, can be achieved.
Two detailed antenna designs based on the aforementioned design approaches are now presented. Both antennas have been designed for use in compact flat panel arrays for low-power applications, also known as small cell deployments.
Figure 4 illustrates a model in three dimensions of an antenna according to one embodiment. The antenna of Figure 4 has been designed to operate in the 2.6 GHz LTE band (LTE deployments in Europe). As shown in Figure 4, an octagonal patch is used as the main radiating element. In the embodiment shown, the surrounding wall is also of octagonal shape. In general, as described above, the surrounding wall does not have to be identical with the shape of the radiating patch; it can be of any shape, provided that there are parts of the circumference of the patch that are in close proximity to the wall.
The antenna of Figure 4 is a dual-polarized antenna, polarized at +/- 45°. In accordance with desired network requirements, a feeding port of one of these polarizations (+45°) has been tuned for operation in the downlink for of the band of interest (2.62-2.69 GHz) and the port of the orthogonal polarization (-45°) has been tuned for operation in the uplink for the band of interest (2.50-2.57 GHz). To satisfy this system requirement, the radiating patch has been kept perfectly symmetrical, and the loading wall has been adjusted such that the gaps between the radiating edges of the +45° polarization patch and the loading wall are larger than the gaps for the -45° polarization. In this way, the loading capacitance of the -45° polarization is larger, and the feeding port for this polarization can be tuned to resonate at a slightly lower frequency.
Figure 5 is a rear view of the antenna of Figure 4. In Figure 5, two pairs of feeding probes as described in relation to Figure 2 are depicted. The exact shape, thickness, and position of these probes have been properly optimized separately for each polarization, such that their total inductance is chosen to match a loading capacitance provided by the surrounding wall. In practice, each pair of probes is fed differentially through an external differential feeding network (for example, PCB-based balun). A rod depicted in the centre of the patch in Figure 5 is used, in this embodiment, to provide mechanical support for the patch and does not influence the electric performance of the antenna.
The footprint of the antenna shown in Figures 4 and 5 is 57mm x 57mm (λ/2 x λ/2 at 2.6 GHz). The profile of the patch is 10mm and the profile of the surrounding wall is 14mm.
Figure 6 shows the simulated S-parameters of the antenna shown in Figures 4 and 5. Figure 6 illustrates that the two feeding ports (one for each pair of probes) are tuned at slightly different frequencies. The -10dB bandwidth of each of these ports is approximately 150 MHz (- 5.5 %) and cross-polarization isolation is below -34 dB everywhere in the band of interest.
Figure 7 illustrates a 1x4 antenna array according to one embodiment. The array shown in Figure 7 comprises four antenna as shown in Figures 4 and 5. The array period of the array of Figure 7 is set to 60mm (λ/2 at 2.5 GHz).
Figure 8 illustrates simulated S-parameters of the array elements of Figure 7. Figure 8 shows that the co-polarization couplings between any pair of adjacent antenna elements in the array remain below -23 dB and do not cause any major problems in the matching of the antenna (for example, detuning). This low value may be attributed to the walls used to load the antenna elements which also contribute to the reduction of any coupling between array elements. It will thus be understood that the proposed antenna element is particularly suitable for use in compact antenna arrays.
In embodiments where larger operating bandwidths are required, such bandwidths can be achieved, for example, by increasing the profile of the antennas without altering their footprint (and thus array configuration). In such embodiments, redesign of the feeding probes (shape and position) of the patches is also required.
Figure 9 illustrates the radiation pattern of the 1x4 array of Figure 7 for the case that the beam is scanned at 30°. According to the radiation pattern, approximately 11dBi of gain can be delivered by the 1x4 antenna array at 30°.
A second antenna design has been developed for operation in the 700 MHz LTE band (LTE deployments in USA). For this band (λ=400mm at 750 MHz), larger miniaturization factors are required, to ensure resulting flat-panel arrays are compact enough to be easily installed on base stations. In this antenna design, the concept illustrated in Figure 3 is utilised.
Figure 10 shows a 3-D model of a proposed antenna according to one embodiment. In the embodiment of Figure 10, a radiating patch is provided in the form of a dual-polarized octagonal patch. A surrounding wall of substantially square cross-section is provided. To achieve a desired miniaturization factor, the surrounding wall is extended at each corner of the square and folded over the octagonal radiating patch, thus increasing an "overlap" area between the patch and the surrounding wall. The exact size of this area and the vertical distance between the patch and the folded part of the wall acts to determine the miniaturization factors that can be achieved.
Figure 11 is a rear view of the antenna of Figure 10. Similar to previously described embodiments, the shape and the position of the feeding probes are optimized to match the loading capacitance.
Figure 12 illustrates simulated S-parameters of the antenna of Figures 10 and 11. In particular, Figure 12 illustrates simulated S-parameters of an antenna 120mm x 120mm (0.3λ x 0.3λ at 750 MHz). The profile of the antenna has been set to 50mm. Similar to before, two signal polarizations have been tuned separately to corresponding downlink and uplink bands. As shown in Figure 12, for both polarizations the return loss remains below -10dB for a bandwidth of approximately 30 MHz (approximately 4%), while the cross-polarization coupling remains below -40 dB.
Figure 13 shows a 2 x 3 antenna array according to one embodiment. The array of Figure 13 comprises six antenna elements according to the embodiment shown in Figure 10. The array period is 140 mm (0.35λ at 750 MHz) and the total array footprint is 430 mm x 340 mm.
Figure 14 shows the simulated S-parameters of an antenna element located in the array of Figure 13. In particular, Figure 14 shows the simulated S-parameters of the antenna element located middle of the upper row of the array are shown in Figure 13. In this array, the coupling between the adjacent elements remains below -13 dB. This coupling value is relatively high and its impact on the input impedance of each array element cannot be considered negligible. Therefore, the elements of such an array have to be tuned in the presence of neighboring elements.
Antenna designs in accordance with embodiments may be employed in compact antenna arrays designed to meet beam-scanning requirements over large solid angles. Given that such applications will be much more popular within the context of 4G cellular systems, the need for such antennas is expected to grow rapidly over the next years.
Benefits of the proposed antenna designs include: a compact footprint, reduced coupling exhibited when used in compact arrays, and a large range of bandwidths over which they can be matched by properly setting their profiles. Such features, together with a low-cost and fully automated fabrication process, for example, 3-D forms made of metalized plastic and mounted on PCBs, make embodiments a promising technology for low-power antenna panels.
Embodiments of the proposed antenna may achieve a large range of footprint miniaturization factors which may be required to form compact antenna arrays, without the use of any dielectric materials. Mechanisms used by some embodiments to achieve miniaturization enable a coupling reduction between elements of compact antenna arrays. Embodiments allow a large range of bandwidth requirements (FBW<20%) to be achieved by properly setting antenna profile together with the position and shape of the feeding probes. Embodiments can be broadband, compact in size, light in weight, deliver high radiating efficiency values and can be fabricated using low-cost materials, for example, metalized plastic mounted on PCBs.
Given that small-cell base stations with 2-D beam scanning properties are becoming more popular, the need for dual-polarized, compact antenna designs for such applications is increasing. Furthermore, low-cost implementations of the proposed antennas, for example, by using 3-D metalized plastic elements mounted on PCBs, make them good candidates for such applications.
The proposed antenna designs have been developed within a framework for use with Active Antenna Arrays.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.
The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claims

A compact patch antenna for use in an antenna array in a wireless telecommunications network, said patch antenna being operable to receive a feed signal and transform said feed signal to a radiated output signal,
said compact patch antenna comprising:
a ground plate;

a radiating element operable to radiate said output signal, said radiating element located substantially parallel to, and spaced from, said ground plate;

a capacitive loading element extending from said ground plate and arranged to define a cavity between said radiating element and said ground plate, said capacitive loading element being spaced from said radiating element to define a predetermined capacitive gap between said radiating element and said capacitive loading element,

said predetermined capacitive gap being selected to alter capacitance of said cavity; and

a differential signal feed mechanism operable to couple said feed signal to said radiating element, and alter inductance of said cavity in a predetermined manner selected to substantially compensate for a reduction in output signal bandwidth caused by said alteration to said cavity capacitance caused by said predetermined capacitive gap.
A compact patch antenna according to claim 1, wherein said capacitive loading element comprises a wall surrounding said radiating element.
A compact patch antenna according to claim 1 or claim 2, wherein said predetermined capacitive gap is defined between an edge of said radiating element and a substantially planar surface of said capacitive loading element.
A compact patch antenna according to claim 1 or claim 2, wherein said predetermined capacitive gap is defined between a portion of a substantially planar surface of said radiating element and a substantially planar surface of said capacitive loading element.
A compact patch antenna according to any preceding claim, further comprising a dielectric material located in said predetermined capacitive gap.
A compact patch antenna according to any preceding claim, wherein said radiating element and said capacitive loading element have a substantially identical shape in cross-section.
A compact patch antenna according to any preceding claim, wherein said differential signal feed mechanism comprises a pair of inductive feed posts.
A compact patch antenna according to claim 7, wherein said inductive feed posts comprise posts increase in cross sectional area along their length.
A compact patch antenna according to claim 8, wherein said inductive feed posts are stepped in cross sectional area.
A compact patch antenna according to any preceding claim, wherein said feed signal has a wavelength of around λ and said compact patch antenna has a footprint of substantially (0.5λ)².
A compact patch antenna according to any preceding claim, wherein said radiating element comprises a dual polarized radiating element, operable to receive two orthogonal input signals and radiate two orthogonal output signals, said capacitive loading element is spaced from said radiating element to define a predetermined capacitive gap for each of said orthogonal signals.
A compact patch antenna according to any preceding claim, formed from metallised plastic.
A method of forming a compact patch antenna for use in an antenna array in a wireless telecommunications network, said patch antenna being operable to receive a feed signal and transform said feed signal to a radiated output signal,
said method comprising:
providing a ground plate;

providing a radiating element operable to radiate said output signal, and locating said radiating element substantially parallel to, and spaced from, said ground plate;

arranging a capacitive loading element extending from said ground plate to define a cavity between said radiating element and said ground plate, said capacitive loading element being spaced from said radiating element to define a predetermined capacitive gap between said radiating element and said capacitive loading element, said predetermined capacitive gap being selected to alter capacitance of said cavity; and

providing a differential signal feed mechanism operable to couple said feed signal to said radiating element, and alter inductance of said cavity in a predetermined manner selected to substantially compensate for a reduction in output signal bandwidth caused by said alteration to said cavity capacitance caused by said predetermined capacitive gap.