Mixed feed for a group antenna with dual-polarized patch antenna elements

Description

TECHNICAL FIELD

[0001] This disclosure relates generally to an antenna array, which comprises dual-polarized antenna elements that are connected to the same feeding network. The dual-polarized antenna elements comprise at least two patch antenna elements, which are connected in a mixed feeding scheme to the feeding network. The mixed feeding scheme is realized by different feeding arrangements for a first polarization and a second polarization of at least two patch antenna elements, wherein the feeding arrangements are designed to mix single-ended feeding and differential feeding.BACKGROUND

[0002] In an antenna array, when closely spaced antenna elements are required, the design of the feeding network signal routing seriously suffers a lack of space. This is specifically valid - but not limited to - mm-wave antenna arrays, where technological constraints strongly limit dual polarization feeding complexity, due to a minimum trace width and a minimum trace-to-trace gap. These technological limitations imply degradations to the performance of the antenna array, like a reduced bandwidth, unequal port impedances, a bad port-to-port isolation, and a non-optimal radiation pattern.

[0003] An antenna array may, for instance, comprise a plurality of dual-polarized patch antenna elements, which can be either aperture-coupled or probe-fed antenna elements. Such patch antenna elements are usually driven by either single-ended feeding or differential feeding.

[0004] It is known that differential feeding provides a larger resonant resistance, more similar co-polar radiation patterns, and a lower cross-polar radiation component, if compared with single-ended feeding. Differential feeding, as exemplarily depicted in FIG. 1(a), may comprise a pair of probes with out-of-phase currents, in order to suppress unwanted leakage radiation and thus to achieve low cross polarization. Nevertheless, also single-ended feeding can be improved in terms of bandwidth and radiation pattern stability for example, by feeding a slot in two symmetrical points from its center, as exemplarily depicted in FIG. 1(b).

[0005] Even though the two feeding methods depicted in FIG. 1 provide the respective benefits mentioned above, using either one these feeding methods to drive a dual-polarized aperture-coupled patch antenna element is difficult, because the required feeding network is complex. In some cases this complexity, which is mainly due to manufacturing and technological constraints (especially at - but not limited to - mm-waves), requires to consider multiple feeding network layers or jumpers or crossovers, as exemplarily shown in FIG. 2 for different examples of feeding arrangements in FIG. 2(a) and 2(b), wherein the jumpers or crossovers are indicated by dotted circles. This leads to a higher manufacturing complexity, and therefore to higher costs.

[0006] The manufacturing complexity (and therefore the costs) is even more relevant in the case of an antenna array of dual-polarized patch antenna elements, because the number of probes required to feed the entire antenna array is twice the number of patch antenna elements. Therefore, the complexity of the feeding network is increased.

[0007] US 2013 / 063310 A1 discloses a microstrip slot feed patch antenna element for a dual-polarized wideband patch antenna.SUMMARY

[0008] The present disclosure and its solutions are based on the desire to reduce the manufacturing complexity of such an antenna array including patch antenna elements, and is based on the following further considerations.

[0009] When the technological constraints do not permit accommodating differential feeding for both polarizations on a single layer of e.g. a substrate, there are essentially two possibilities to maintain the manufacturing complexity, as well as the costs, as low as possible: 1. A first possibility is to drive dual-polarized aperture-coupled patch antenna elements by exploiting single-ended feeding, in particular, corner-feeding or edge-feeding, as exemplarily depicted in FIG. 3(a). This comparatively simple feeding method permits routing the feeding lines on a single layer, and shows identical input impedances for both polarizations. However, this feeding method does not provide a high port-to-port isolation, or a high cross polar discrimination (XPD), or symmetrical radiation patterns. 2. A second possibility is to drive dual-polarized aperture-coupled patch antenna elements in the following way: one polarization is fed with single-ended feeding (e.g., centered, with a single probe or a double probe), and the second polarization is fed with differential feeding, as exemplarily depicted in FIG. (3b). This approach provides sufficiently high port-to-port isolation and XPD, as well as more symmetrical radiation patterns. However, the operating bandwidth, the input impedances, and the radiation patterns of the two polarizations may show relevant differences.

[0010] The above feeding methods can also be exploited to feed an antenna array of more than one dual-polarized aperture-coupled or probe-fed patch antenna element, as exemplarily depicted in FIG. 4(a) for the first feeding method and in FIG. 5(a) for the second feeding method. Both feeding methods are particularly depicted for the case of a 2-by-1 cluster of patch antenna elements.

[0011] The antenna array with the single-ended corner feeding - which is shown in FIG. 4(a) - provides identical input impedances for the two polarizations, but lacks in terms of bandwidth (see FIG. 4(b), showing a return loss for each polarization ("Port1" and "Port2" are for different polarizations)). The antenna array with the single-ended centered feeding for the first polarization and with the differential feeding for the second polarization - which is shown in FIG. 5(a) - provides symmetrical radiation patterns, but the two polarizations show different input impedances and operating bandwidths (see FIG. 5(b) showing a return loss for each polarization (port)).

[0012] If the two polarizations behave differently in terms of input impedance, bandwidth, and radiation patterns, this could have a negative impact on the whole antenna system including the antenna array, for the following reasons: firstly, the active / passive components connected to the antenna array could require different impedance matchings for the two polarizations; secondly, a calibration system could be required to address differently the two polarizations; thirdly, the antenna system therefore cannot be assumed to perform identically in the two polarizations in terms of operating bandwidth and effective isotropic radiated power (EIRP).

[0013] In view of the above, the present disclosure aims to improve the feeding of an antenna array comprising dual-polarized patch antenna elements. An objective is to provide a feeding method for the antenna array, which combines the advantages of single-ended feeding and differential feedings, while exploiting only a single feeding layer. Multiple feeding network layers or jumpers or crossovers should be avoided. The antenna array should accordingly be manufacturable with a low complexity. Another objective is to provide the antenna array with one or more of a wide bandwidth, a high port-to-port isolation, and a high XPD. Another objective is that the antenna array shows an identical behavior in terms of input impedances and has symmetrical radiation patterns.

[0014] These and other objectives are achieved by the solutions of this disclosure as described in the independent claims. Advantageous implementations are further described in the dependent claims.

[0015] A first aspect of this disclosure provides an antenna array comprising: a feeding network; a plurality of dual-polarized antenna elements, wherein each of the dual-polarized antenna elements is connected to the feeding network and is configured to radiate with a first polarization and with a second polarization; wherein the plurality of dual-polarized antenna elements comprises a first patch antenna element and a second patch antenna element; and wherein the feeding network comprises: a first feeding arrangement for the first polarization, the first feeding arrangement being configured to feed the first patch antenna element by single-ended feeding and the second patch antenna element by differential feeding; and a second feeding arrangement for the second polarization, the second feeding arrangement being configured to feed the first patch antenna element by differential feeding and the second patch antenna element by single-ended feeding.

[0016] The antenna array of the first aspect exploits the advantages of both single-ended feeding and differential feeding. For example, the antenna elements of the antenna array can be driven by the feeding arrangements provided on a single feeding layer. The antenna array of the first aspect does also not require any jumpers or crossovers. The antenna array can thus be manufactures with a low complexity. The antenna array in addition shows good characteristic, for example, a wide bandwidth, a high port-to-port isolation, and a high XPD. The behavior of the input impedances is more or less identical, and the antenna array can radiate with symmetrical or almost symmetrical radiation patterns.

[0017] Notably, in this disclosure, an antenna element is a radiating element, i.e., the antenna element is configured to radiate a radio wave in response to a radiofrequency (RF) signal fed to the antenna element. This RF signal can be fed by the feeding arrangements, respectively, for the two polarizations of the antenna elements. A feeding arrangement may comprise at least feeding lines to feed the respective RF signals to the antenna elements. However, a feeding arrangement can include further components, like amplifiers, delay elements, phase shifters, splitters etc.

[0018] In an implementation form of the first aspect, the plurality of dual-polarized antenna elements comprises a set of four or more patch antenna elements including the first patch antenna element and the second patch antenna element, and the set of patch antenna elements comprises: a first subset including the first patch antenna element, wherein the first feeding arrangement is configured to feed each patch antenna element of the first subset by single-ended feeding and the second feeding arrangement is configured to feed each patch antenna element of the first subset by differential feeding; a second subset including the second patch antenna element, wherein the first feeding arrangement is configured to feed each patch antenna element of the second subset by differential feeding and the second feeding arrangement is configured to feed each patch antenna element of the second subset by single-ended feeding.

[0019] In this way, an antenna array with an arbitrary number of antenna elements can be designed, which enjoys the above-mentioned advantages of the mixed feeding scheme, i.e., the respective feeding with the single-ended feeding and the differential feeding.

[0020] In an implementation form of the first aspect, the patch antenna elements of the set are arranged one after the other in a linear array; and the patch antenna elements of the first subset are arranged alternatingly with the patch antenna elements of the second subset in the linear array.

[0021] This implements the mixed feeding scheme in a linear antenna array, where the antenna elements are arranged after each other along a determined direction.

[0022] In an implementation form of the first aspect, the patch antenna elements of the set are arranged in a planar array; and the patch antenna elements of the first and the second subset are arranged such that each patch antenna element of the first subset has at least one adjacent patch antenna element of the second subset in the planar array.

[0023] This implements the mixed feeding scheme in a planar antenna array, where the antenna elements are arranged in one or more rows and / or columns, for instance, in a matrix-like arrangement.

[0024] In an implementation form of the first aspect, the antenna array comprises a 4-by-1 or a 2-by-2 array of patch antenna elements.

[0025] In an implementation form of the first aspect, the first feeding arrangement comprises two first differential feeding elements coupled to the second patch antenna element, the two first differential feeding elements being arranged off-centered with respect to the center of the second patch antenna element; and / or the second feeding arrangement comprises two second differential feeding elements coupled to the first patch antenna element, the two second differential feeding elements being arranged off-centered with respect to the center of the first patch antenna element.

[0026] In an implementation form of the first aspect, the two first differential feeding elements are arranged symmetrically with respect to the center of the second patch antenna element; and / or the two second differential feeding elements are arranged symmetrically with respect to the center of the first patch antenna element.

[0027] These implementation forms provide the above-mentioned advantages of the differential feeding in the best way.

[0028] In an implementation form of the first aspect, the first feeding arrangement comprises a first single-ended feeding element coupled to the first patch antenna element, the first single-ended feeding element being arranged at the center of the first patch antenna element; and / or the second feeding arrangement comprises a second single-ended feeding element coupled to the second patch antenna element, the second single-ended feeding element being arranged at the center of the second patch antenna element.

[0029] This provided the above-mentioned advantages of the single-ended feeding in the best way.

[0030] In an implementation form of the first aspect, the first single-ended feeding element comprises a first slot aperture; and / or the second single-ended feeding element comprises a second slot aperture.

[0031] In an implementation form of the first aspect, the two first differential feeding elements comprise a first pair of slot apertures; and / or the two second differential feeding elements comprise a second pair of slot apertures.

[0032] In an implementation form of the first aspect, each slot aperture is formed in the first or second patch antenna element it is coupled to, or is formed in a substrate arranged adjacent to the first or second patch antenna element it is coupled to.

[0033] The above implementations are beneficial for an antenna array with aperture-coupled antenna elements.

[0034] In an implementation form of the first aspect, the first single-ended feeding element comprises a first feed probe; and / or the second single-ended feeding element comprise a second feed probe.

[0035] In an implementation form of the first aspect, the two first differential feeding elements comprise a first pair of feed probes; and / or the two second differential feeding elements comprise a second pair of feed probes.

[0036] The above implementations are beneficial for an antenna array with probe-fed antenna elements.

[0037] In an implementation form of the first aspect, the feeding network comprises a microstrip feeding network provided on a single layer of a substrate or routed on different layers of the substrate.

[0038] In an implementation form of the first aspect, the slot apertures are formed in a single layer of the substrate or in different layers of the substrate.

[0039] In any case, crossovers or jumpers can be avoided, leading to a lower manufacturing complexity.

[0040] In an implementation form of the first aspect, the substrate comprises a reflector plane, and the plurality of dual-polarized antenna elements are arranged on the reflector plane.

[0041] Thus, the radiation characteristics of the antenna array can be improved.

[0042] In an implementation form of the first aspect, the first feeding arrangement is configured to feed the first patch antenna element and the second patch antenna element with a respective phase shift and / or amplitude unbalance between the first patch antenna element and the second patch antenna element; and / or the second feeding arrangement is configured to feed the first patch antenna element and the second patch antenna element with a respective phase shift and / or amplitude unbalance between the first patch antenna element and the second patch antenna element.

[0043] In an implementation form of the first aspect, the first feeding arrangement is configured to feed the patch antenna elements of at least one of the first subset and the second subset with a respective phase shift and / or amplitude unbalance between adjacent patch antenna elements; and / or the second feeding arrangement is configured to feed the patch antenna elements of at least one of the first subset and the second subset with a respective phase shift and / or amplitude unbalance between adjacent patch antenna elements.

[0044] These implementation forms have the benefit that the radiation pattern of the antenna array can be conveniently shaped and / or tilted.

[0045] A second aspect of this disclosure provides a method for operating an antenna array comprising a plurality of dual-polarized antenna elements, wherein each of the antenna elements is configured to radiate with a first polarization and with a second polarization, and wherein the plurality of dual-polarized antenna elements comprises a first patch antenna element and a second patch antenna element; and wherein the method comprises: operating the antenna array to radiate with the first polarization, wherein the first patch antenna element is fed by single-ended feeding and the second patch antenna element is fed by differential feeding; and operating the antenna array to radiate with the second polarization, wherein the first patch antenna element is fed by differential feeding and the second patch antenna element is fed by single-ended feeding.

[0046] In an implementation form of the second aspect, the antenna array is operated to radiate with the first polarization and the second polarization at the same time or one after the other.

[0047] Notably, the method of the second aspect may operate an antenna array of the first aspect and its implementation forms described above. That is, the method of the second aspect may have implementation forms corresponding to the implementation forms of the antenna array of the first aspect. The method of the second aspect accordingly achieves all advantages of the antenna array of the first aspect, as they are explained above.

[0048] In summary, the solutions proposed by this disclosure provide a feeding network for an antenna array (may be a sub-array of an antenna system) of dual polarized, for example aperture-coupled or probe-fed, patch antenna elements. The feeding network, particularly the feeding arrangements, may be arranged on a single layer, for example of a substrate, which guarantees an identical behavior in terms of input impedance, together with a wide band operation (a wide bandwidth (≥20%)), a high port-to-port isolation, a high XPD, and symmetrical radiation patterns.

[0049] Accordingly, the solutions proposed by this disclosure are able to obtain all the benefits mentioned above for each of the differential feeding and the single-ended feeding, while requiring only a single feeding layer and no jumpers or crossovers.

[0050] It has to be noted that devices, elements, units and means described in the present application could be implemented using software or hardware elements or any kind of combination thereof. Functionalities described to be performed by various elements are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented using respective software or hardware elements, or any kind of combination thereof.BRIEF DESCRIPTION OF DRAWINGS

[0051] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which FIG. 1shows exemplary feeding methods for a single-polarized aperture couple patch antenna element, in particular, (a) differential feeding and (b) single-ended feeding with dual symmetrical feed points. FIG. 2shows exemplary dual polarization aperture-coupled patch antenna elements with (a) single-ended centered feeding with a crossed slot and dual symmetrical feed points requiring multiple feeding network layers or jumpers or crossovers and (b) differential feeding requiring multiple feeding network layers or jumpers or crossovers. FIG. 3shows exemplary dual polarization aperture-coupled patch antenna elements with: (a) single-ended corner feeding, and (b) single-ended feeding (centered) for the first polarization plus a differential feeding for the second polarization. FIG. 4shows (a) an exemplary 2-by-1 antenna array with a conventional feeding method in which both polarizations are fed with single-ended corner feeding and (b) shows the related return loss. FIG. 5shows (a) an exemplary 2-by-1 antenna array with a conventional feeding method in which one polarization is driven with single-ended feeding only while the other polarization with differential feeding only and (b) shows the related return loss. FIG. 6shows in (a) a bandwidth comparison between single-ended feeding and differential feeding for an antenna element as shown in FIG 3; shows in (b) an exemplary dual-polarized aperture-coupled patch antenna element with a differential feeding for both polarizations with non-symmetric feeding lines; and shows resonance locations (a) for single-ended feeding and differential feeding, and (b) when mixing the feeding mechanisms. FIG. 7shows an antenna array according to an embodiment of this disclosure. FIG. 8shows an antenna array according to an embodiment of this disclosure with the mixed feeding scheme in which each polarization is driven with both single-ended and differential feedings. FIG. 9shows a surface current distribution on the driven patch antenna element for (a) single-ended edge (or corner) feeding, and (b) single-ended center feeding and (c) differential feeding. FIG. 10shows scattering parameters for an antenna array according to an embodiment of this disclosure. FIG. 11shows an example of a 2-by-1 array, wherein (a) shows a conventional feeding method in which both polarizations are fed with single-ended feeding only, and (d) shows the related return loss; (b) shows another conventional feeding method in which one polarization is driven with single-ended feeding only while the other polarization with differential feeding only, and (e) shows the related return loss at the input ports that are different; and (c) shows the mixed feeding scheme of this disclosure in which each polarization is driven with both single-ended and differential feedings, and (f) shows the related return loss at the input ports that are identical. FIG. 12shows a radiation pattern symmetry comparison (single-ended feeding depicted in FIG. 11(a), mixed feeding scheme depicted in FIG. 11(c), wherein (a) shows a radiation pattern at an elevation of 0°; and (b) shows a radiation pattern at an elevation of 10°. FIG. 13shows exemplary 4-by-1 and 2-by-2 antenna arrays according to embodiments of this disclosure with two levels of mixing (a) simple, and (b) double. FIG. 14shows a method according to an embodiment of this disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

[0052] According to the solution of this disclosure, a mixed feeding for an antenna array - including a plurality of dual-polarized patch antenna elements connected to the same feeding network - is presented to exploit the advantages of two different feeding methods, namely of single-ended feeding and differential feeding (e.g., as depicted in FIG. 6(a) for the patch antenna element of FIG. 3(b)). Single-ended feeding is simple and needs a relatively small area for signal routing, while its operating bandwidth is not extremely wide (<20%). Differential feeding is a bit more complex and needs a larger area for signal routing, but provides a wider operating bandwidth (>20%). With differential feeding it is possible to excite the patch antenna element obtaining two radiating modes (e.g., TM10 and TM30) and a dual-resonance effect that widens the bandwidth. Furthermore when the single-ended feeding is off-centered, as depicted in FIG. 3(a), it is possible to obtain the feeding lines in a symmetric way, and to obtain the same input impedance for the two polarizations. On the other hand, when the differential feeding is routed on a single layer (if possible in terms of size and technological constraints), it is not possible to design the feeding lines in a symmetric fashion, and therefore the two polarizations will show a different input impedance. An example of such a patch antenna element is shown in FIG. 6(b), wherein a specific differential feeding is realized. However, modifications may be made to the feeding lines by keeping the proper excitation phases and amplitudes at the slots.

[0053] For a dual-polarized antenna array, the proposed solution of this disclosure allows to combine the two feeding mechanisms (single-ended and differential feeding), in order to obtain similar or identical feeding lines for the two polarizations.

[0054] For example FIG. 7 shows an embodiment of an antenna array 700 according to this solution of the disclosure. The antenna array 700 may be referred to as a dual-polarized antenna array 700.

[0055] In particular, the antenna array 700 a plurality of dual-polarized antenna elements, wherein each of the dual-polarized antenna elements is connected to the same feeding network 705 of the antenna array 700. Further, each antenna element is configured to radiate with a first polarization and with a second polarization. The plurality of dual-polarized antenna elements comprises a first patch antenna element 701 and a second patch antenna element 702, but may comprise more patch antenna elements. As an example, the antenna array 700 may comprise a 4-by-1 or a 2-by-2 array of patch antenna elements. The antenna array 700 may in addition also comprise other dual-polarized antenna elements, so that the patch antenna elements may form a sub-array of the antenna array 700.

[0056] The feeding network comprises a first feeding arrangement 705a for the first polarization, and a second feeding network 705b for the second polarization. That is, the first feeding arrangement 705a may be configured to provide a first RF signal to the at least two patch antenna elements 701, 702, and the patch antenna elements 701, 702 are configured to radiate with a first polarization in response to the first RF signal. The second feeding arrangement 705b may be configured to provide a second RF signal to the at least two patch antenna elements 701, 702, and the patch antenna elements 701, 702 are configured to radiate with a second polarization in response to the second RF signal. The first polarization may be orthogonal to the second polarization.

[0057] The first feeding arrangement 705a is configured to feed the first patch antenna element 701 by single-ended feeding - for example via a single-ended feeding elements 703a like a feed probe or a slot aperture - and the second patch antenna element 702 by differential feeding - for example via a differential feeding element 704a like a pair of feed probes or a pair of slots. The second feeding arrangement 705b is configured to feed the first patch antenna element 701 by differential feeding - for example via a differential feeding elements 704b like a pair of feed probes or a pair of slots - and the second patch antenna element 702 by single-ended feeding - for example via a single-ended feeding element 703b like a feed probe or a slot aperture.

[0058] In addition to the above-described, a proper mix of differential feeding and single-ended feeding for the same polarization can be suitably exploited, in order to combine different resonating effects that contribute to widening the operating bandwidth. In other words, the resonances of the single-ended feeding and differential feeding can be conveniently designed to be slightly shifted in frequency, in order to obtain a wide-band impedance matching. As an example, FIG. 6(c) shows a case, in which the single-ended feeding has - as expected - a narrower bandwidth with respect to the differential feeding, and the two feeding versions have different resonating frequencies. By properly combining these resonances, it is possible to obtain a wide operating bandwidth, as demonstrated in FIG. 6(d). This combination may be achieved by alternatively driving each polarization with single-ended and differential feedings. However, generally, the antenna array 700 can be operated to radiate with the first polarization and the second polarization at the same time or one after the other.

[0059] FIG. 8 shows an antenna array 700 according to an embodiment of this disclosure with the mixed feeding scheme, in which each polarization is driven with both single-ended and differential feedings, and in which the combination of resonances shown in Fig. 6(b) can be achieved. The antenna array 700 of FIG. 8 builds on that on FIG. 7. Same elements are labelled with the same reference signs and implemented in a similar manner in these figures.

[0060] FIG. 8 shows that in the antenna array 700, the first feeding arrangement 705a and the second feeding arrangement 705b, which are part of the feeding network 705, may be provided on a single layer of a substrate 800. The feeding network 705 may, for example, comprise or be a microstrip feeding network provided on the single layer of a substrate 800. However, it could also be routed on different layers of the substrate 800. The substrate 800 may, for example, comprise a reflector plane, wherein the plurality of dual-polarized antenna elements, particularly the first and second patch antenna element 701, 702, may be arranged on the reflector plane. Each feeding arrangement 705a, 705b may comprise a respective port, for instance, to provide a respective RF signal to feed the first or second polarization.

[0061] In the antenna array 700 of FIG. 8, the first feeding arrangement 705a comprises a first single-ended feeding element 703a coupled to the first patch antenna element 701, and the first single-ended feeding element 703a is arranged at the center of the first patch antenna element 701 (e.g., geometric center). Further, the first feeding arrangement 705a also comprises two first differential feeding elements 704b coupled to the second patch antenna element 702, and the two first differential feeding elements 704a are arranged off-centered with respect to the center of the second patch antenna element 702.

[0062] The second feeding arrangement 705b comprises a second single-ended feeding element 703b coupled to the second patch antenna element 702, and the second single-ended feeding element 703b is arranged at the center of the second patch antenna element 702. Further, the second feeding arrangement 705b also comprises two second differential feeding elements 704b coupled to the first patch antenna element 701, and the two second differential feeding elements 704b are arranged off-centered with respect to the center of the first patch antenna element 701.

[0063] There are different way to implement the single-ended feeding elements and the differential feeding elements. For example, a single-ended feeding element may be or comprise a slot aperture. Alternatively, a single-ended feeding element may be or comprise a feed probe. A differential feeding element may be or comprise a pair of slot apertures, or a pair of feed probes. A feed probe can be provided on the patch antenna element it is coupled to. A slot aperture can be formed in the first or second patch antenna element it is coupled to, or in the substrate 800 adjacent to the patch antenna element it is coupled to.

[0064] Two differential feeding elements for the same patch antenna element may be arranged symmetrically with respect to the center of that patch antenna element. The combination of the two feeding mechanisms on each patch antenna element 701, 702, as depicted in FIG. 8, which are centered with respect the respective patch antenna element 701, 702, may guarantee symmetrical radiation patterns. This effect is related to the fact that when the patch antenna element is fed symmetrically with respect to its center, then the surface current distribution is symmetric as well (two symmetry planes on the patch antenna element may be identified) and the radiation pattern will be then much more symmetric with respect to the case of a corner-fed (or edge-fed) patch antenna element. An example of surface current distribution on one of the driven patch antenna elements is depicted in FIG. 9. Thereby, FIG. 9(a) shows a surface current distribution for a single-ended edge or corner-fed patch antenna element, FIG. 9(b) for a single-ended center-fed patch antenna element, and FIG. 9(c) for a differentially fed patch antenna element.

[0065] The proposed solution provides the following advantages: The feeding network 105 can be on a single layer of a substrate 800 (no use of jumpers, crossovers or routing on multiple layers); A wide operating bandwidth (≥20%); A high port-to-port cross polarization isolation (>30dB); An identical input impedance for the two polarizations; An improved radiation pattern symmetry.

[0066] In this respect, FIG. 10 shows scattering parameters for an antenna array according to an embodiment of this disclosure. In particular, FIG. 10 shows a high port-to-port isolation (curve 1000), and shows an identical return loss for the two polarizations ("Port1", "Port 2"; curve 1001).

[0067] In the following, some further details of the solution of this disclosure in comparison with conventional solutions are described. Thereby, the description assumes a dual slant-45 polarized configuration, however, it will be apparent to those skilled in the art that modifications to the antenna polarization may be made without departing from the main idea of this disclosure. Accordingly, it is not intended that the present disclosure is limited, except as may be necessary in view of the appended claims.

[0068] For the sake of simplicity, a 2-by-1 antenna array 700 of dual polarized aperture-coupled stacked patch antenna elements is considered. The feeding lines (e.g., micro-strips or striplines) lie on a single layer of a substrate 800.

[0069] One way to excite the patch antenna elements exploits only single-ended feeding for both polarizations, as shown in FIG. 11(a). This conventional concept is simple to design and shows identical input impedances for the two polarizations. However, it has two main drawbacks: firstly, its operating bandwidth is not wide (generally <20%; see FIG. 11(b)); secondly, the off-centered feeding can generate asymmetry in the radiation patterns (see FIG. 12(a) and (b), curve 1200).

[0070] Another way to excite the patch antenna elements exploits only single-ended feeding for one polarization and only differential feeding for the second polarization, as depicted in FIG. 11(b). This concept maintains simplicity and pattern symmetry, but has two main drawbacks: firstly, the two polarizations show different operating bandwidths (see FIG. 11(e)); secondly input impedances for the two polarizations are different (see also FIG. 11(e)).

[0071] The solution of this disclosure is shown in FIG. 11(c). In particular, FIG. 11(c) shows an antenna array 700 according to an embodiment of this disclosure, which builds on the embodiment shown in FIG. 7 and 8. Same elements are labelled with the same reference signs in these figures and function likewise.

[0072] The antenna array 700 of FIG. 7 exploits again a suitably mix of single-ended feeding and differential feeding. Thus, it takes advantage of the benefits of both feeding mechanisms, and permits to obtain: firstly, a wide operating bandwidth (>20%) for both polarizations; secondly, identical input impedances for both polarizations (see FIG. 11(f)); thirdly, symmetrical radiation patterns (see FIG. 12(a) and (b), curve 1201).

[0073] FIG. 12 shows a radiation pattern symmetry comparison (single-ended feeding depicted in FIG. 11(a) and mixed feeding scheme of this disclosure depicted in FIG. 11(c), wherein FIG. 12(a) shows a radiation pattern at an elevation of 0° and (b) shows a radiation pattern at an elevation of 10°.

[0074] The concept of this disclosure can be extended to larger antenna arrays 700. Examples are depicted in FIG. 13. In particular, FIG. 13(a), (b), and (c) show antenna arrays 700 according to embodiments of this disclosure, and build on FIG. 7, 8 and 11. Same elements in these figures share the same reference signs and can be implemented likewise.

[0075] In particular, the antenna array 700 of FIG. 13(a) comprises a 4-by-1 array of patch antenna elements, and the antenna arrays 700 of FIG. 13(b) and 13(b) comprises a 2-by-2 array of patch antenna elements. In all three cases, the plurality of dual-polarized antenna elements comprises a set of four or more patch antenna elements 701, 702, 1301, 1302 including the first patch antenna element 701 and the second patch antenna element 702. Further, the set of patch antenna elements comprises a first subset including the first patch antenna element 701 and a third patch antenna element 1301, and comprises a second subset including the second patch antenna element 702 and fourth patch antenna element 1302. The first feeding arrangement 705a is configured to feed each patch antenna element 701, 1101 of the first subset by single-ended feeding and the second feeding arrangement 105b is configured to feed each patch antenna element 701, 1101 of the first subset by differential feeding. In the other way around, the first feeding arrangement is configured to feed each patch antenna element 702, 1102 of the second subset by differential feeding, and the second feeding arrangement 705b is configured to feed each patch antenna element 702, 1102 of the second subset by single-ended feeding.

[0076] In FIG. 13(a) the patch antenna elements 701, 702, 1301, 1302 of the set are arranged one after the other in a linear array 700L. As can be seen, the patch antenna elements 701, 1301 of the first subset are arranged alternatingly with the patch antenna elements of the second subset 702, 1302 in the linear array 700L.

[0077] In FIG. 13(b) and (c), the patch antenna elements 701, 702, 1301, 1302 of the set are arranged in a planar array 700P. As can be seen, the patch antenna elements 701, 1301 of the first subset and the patch antenna elements 702, 1302 of the second subset are arranged such that each patch antenna element 701, 1301 of the first subset has at least one adjacent patch antenna element 702, 1302 of the second subset in the planar array 700P.

[0078] An even number of patch antenna elements in the antenna array 700 may guarantee the same input impedance for the two ports (i.e., two polarizations, each port is associated with one polarization). However the broadening effect on the operating bandwidth and the pattern symmetry may be guaranteed also with an odd number of patch antenna elements in the antenna array.

[0079] FIG. 14 shows a method 1400 for operating an antenna array 700, wherein the antenna array 700 comprise a plurality of dual-polarized antenna elements, wherein each of the antenna elements is configured to radiate with a first polarization and with a second polarization, and wherein the plurality of dual-polarized antenna elements comprises a first patch antenna element 701 and a second patch antenna element 702. In other words, the method 1400 may be for operating an antenna array 700 according to the FIGs. 7, 8, 11 or 13.

[0080] The method 1400 comprises a step 1401 of operating the antenna array 700 to radiate with the first polarization, wherein the first patch antenna element 701 is fed by single-ended feeding and the second patch antenna element 702 is fed by differential feeding. Further, the method 1400 comprises a step 1402 of operating the antenna array 700 to radiate with the second polarization, wherein the first patch antenna element (701) is fed by differential feeding (704b) and the second patch antenna element 702 is fed by single-ended feeding.

[0081] The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed subject matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. An antenna array (700) comprising: a feeding network (705); a plurality of dual-polarized antenna elements, wherein each of the dual-polarized antenna elements is connected to the feeding network (705) and is configured to radiate with a first polarization and with a second polarization; wherein the plurality of dual-polarized antenna elements comprises a first patch antenna element (701) and a second patch antenna element (702); and wherein the feeding network (705) comprises a first feeding arrangement (705a) for the first polarization and a second feeding arrangement (705b) for the second polarization, and is characterized by: the first feeding arrangement (705a) being configured to feed the first patch antenna element (701) by single-ended feeding (703a) and the second patch antenna element (702) by differential feeding (704a); and the second feeding arrangement (705b) being configured to feed the first patch antenna element (701) by differential feeding (704b) and the second patch antenna element (702) by single-ended feeding (703b).

2. The antenna array (700) according to claim 1, wherein: the plurality of dual-polarized antenna elements comprises a set of four or more patch antenna elements (701, 702, 1301, 1302) including the first patch antenna element (701) and the second patch antenna element (702), and the set of patch antenna elements comprises: a first subset including the first patch antenna element (701), wherein the first feeding arrangement (705a) is configured to feed each patch antenna element (701, 1301) of the first subset by single-ended feeding (703a) and the second feeding arrangement (105b) is configured to feed each patch antenna element (701, 1301) of the first subset by differential feeding (704b); a second subset including the second patch antenna element (702), wherein the first feeding arrangement (705a) is configured to feed each patch antenna element (702, 1302) of the second subset by differential feeding (704a) and the second feeding arrangement (705b) is configured to feed each patch antenna element (702, 1302) of the second subset by single-ended feeding (703b).

3. The antenna array (700) according to claim 2, wherein: the patch antenna elements (701, 702, 1301, 1302) of the set are arranged one after the other in a linear array (700L); and the patch antenna elements (701, 1301) of the first subset are arranged alternatingly with the patch antenna elements of the second subset (702, 1302) in the linear array (700L).

4. The antenna array (700) according to claim 2, wherein: the patch antenna elements (701, 702, 1301, 1302) of the set are arranged in a planar array (700P); and the patch antenna elements (701, 1301, 702, 1302) of the first and the second subset are arranged such that each patch antenna element (701, 1301) of the first subset has at least one adjacent patch antenna element (702, 1302) of the second subset in the planar array (700P).

5. The antenna array (700) according to one of the claims 1 to 4, wherein the antenna array (700) comprises a 4-by-1 or a 2-by-2 array of patch antenna elements (701, 702, 1301, 1302).

6. The antenna array (700) according to one of the claims 1 to 5, wherein: the first feeding arrangement (705a) comprises two first differential feeding elements (704a) coupled to the second patch antenna element (702), the two first differential feeding elements (704a) being arranged off-centered with respect to the center of the second patch antenna element (702); and / or the second feeding arrangement (705b) comprises two second differential feeding elements (704b) coupled to the first patch antenna element (701), the two second differential feeding elements (704b) being arranged off-centered with respect to the center of the first patch antenna element (701).

7. The antenna array (700) according to claim 6, wherein: the two first differential feeding elements (704a) are arranged symmetrically with respect to the center of the second patch antenna element (702); and / or the two second differential feeding elements (704b) are arranged symmetrically with respect to the center of the first patch antenna element (701).

8. The antenna array (700) according to one of the claims 1 to 7, wherein: the first feeding arrangement (705a) comprises a first single-ended feeding element (703a) coupled to the first patch antenna element (701), the first single-ended feeding element (703a) being arranged at the center of the first patch antenna element (701); and / or the second feeding arrangement (705b) comprises a second single-ended feeding element (703b) coupled to the second patch antenna element (702), the second single-ended feeding element (703b) being arranged at the center of the second patch antenna element (702).

9. The antenna array (700) according to claim 8, wherein: the first single-ended feeding element (703a) comprises a first slot aperture; and / or the second single-ended feeding element (703a) comprises a second slot aperture.

10. The antenna array (700) according to one of the claims 6 to 9, wherein: the two first differential feeding elements (704a) comprise a first pair of slot apertures; and / or the two second differential feeding elements (704b) comprise a second pair of slot apertures.

11. The antenna array (700) according to claim 9 or 10, wherein: each slot aperture is formed in the first or second patch antenna element (701, 702) it is coupled to, or is formed in a substrate arranged adjacent to the first or second patch antenna element (701, 702) it is coupled to.

12. The antenna array (700) according to claim 8, wherein: the first single-ended feeding element (703a) comprises a first feed probe; and / or the second single-ended feeding element (703b) comprise a second feed probe.

13. The antenna array (700) according to claim 6 or 12, wherein: the two first differential feeding elements (704a) comprise a first pair of feed probes; and / or the two second differential feeding elements (704b) comprise a second pair of feed probes.

14. The antenna array (700) according to one of the claims 1 to 13, wherein: the feeding network (705) comprises a microstrip feeding network provided on a single layer of a substrate (800) or routed on different layers of the substrate (800).

15. A method (1400) for operating an antenna array (700) comprising a plurality of dual-polarized antenna elements, wherein each of the antenna elements is configured to radiate with a first polarization and with a second polarization, and wherein the plurality of dual-polarized antenna elements comprises a first patch antenna element (701) and a second patch antenna element (702); and wherein the method (1400) comprises operating (1401) the antenna array (700) to radiate with the first polarization and operating (1402) the antenna array (700) to radiate with the second polarization, and is characterized in that: for operating (1401) the antenna array (700) to radiate with the first polarization, the first patch antenna element (701) is fed by single-ended feeding (703a) and the second patch antenna element (702) is fed by differential feeding (704a); and for operating (1402) the antenna array (700) to radiate with the second polarization, the first patch antenna element (701) is fed by differential feeding (704b) and the second patch antenna element (702) is fed by single-ended feeding (703b).