Antenna structure

Abstract

An antenna structure (600, 700, 800, 900) comprising: a first stacked radiating structure (601, 701, 901) comprising a plurality of radiators (604, 605, 704, 705), wherein each radiator is located in a respective stacked layer; a second stacked radiating structure (602, 702, 902) comprising a plurality of radiators (606, 607, 706, 707), wherein each radiator is stacked in a respective stacked layer; a branch feed network (611, 612, 711, 712, 909, 910) for providing signals to the radiators (604, 605, 606, 607, 704, 705, 706, 707), the feed network comprising a first branch (611, 711, 909) for feeding one radiator (604, 606, 704, 707) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702) and a second branch (612, 712, 910) for feeding another radiator (605, 607, 705, 706) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702). Feeding the antenna structure in this way can improve efficiency, increase the degree of freedom in the design of the feed network, thereby enabling better decoupling, greater bandwidth and lower cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to antennas, and in particular to antenna structures comprising a plurality of stacked radiating structures fed by a branching feed network. BACKGROUND

[0002] An antenna is a transducer that converts radio frequency currents into electromagnetic waves, which are then radiated into space.

[0003] With the deployment of Long-Term Evolution (LTE) being substantially complete, operators need to prepare their networks for the upcoming 5G. One of the key technologies to enable the new generation of mobile communications is the multiple input multiple output (MIMO) technology below 6 GHz.

[0004] However, new deployments face limitations from the traditional industry. Regulations in most countries, especially in Europe, are the real limiting factor for deploying new services and infrastructure, and their development speed is likely to be slower than that of the required technology.

[0005] To facilitate site selection and meet local regulations regarding site upgrades, the size of the new antenna should be comparable to that of the traditional product. In addition, in order to be able to maintain the mechanical support structure of the site, the wind load of the new antenna should be comparable to that of the traditional product. These factors can result in a very strict limitation on the width of the antenna.

[0006] It is well known that the directivity of an antenna is limited by its aperture, and therefore by its width. This effect becomes very severe when multiple arrays are placed in the same enclosure. Therefore, antenna arrays placed in small reflectors typically exhibit a wider horizontal beamwidth.

[0007] In stacked antenna arrays, the radiators of one layer are connected to the radiators stacked above them. Figure 1 (a) and Figure 1 Figures (a) and (b) show, respectively, a perspective view and a vertical cross-sectional view of an example of a stacked radiating structure 100 comprising an upper radiator 101 and a lower radiator 102. The stacked radiators 101 and 102 can have significantly different input impedances, and their combination results in a combined radiator that is difficult to match for a specific bandwidth and phase difference.

[0008] As Figure 2As shown, the combined radiating structure 100 traditionally uses a feed circuit to feed both radiators of the stacked radiating structure 100, i.e. radiator 101 and radiator 102. An antenna reflector for a stacked radiating structure is shown as 103. The feed circuit 104 can include a phase shifter 105 that creates a phase shift between the respective signals feeding the radiator 101 and the radiator 102.

[0009] Figure 3 A schematic diagram showing the feeding of an antenna array 300 comprising multiple stacked radiating structures of type 100 is shown. Traditionally, the feeding in the array is performed by feeding each stacked structure and connecting the feed lines for the resulting stacked radiating structures at an antenna port 106.

[0010] Furthermore, it is also possible to stack more radiators along the z-axis. For example, WO 2022 / 028669 Al discloses an antenna array, an example of which is shown in Figure 4 stacking multiple radiators in the z-direction in order to increase the number of clusters 401 (sub-arrays) without increasing the aperture area. The more clusters, the more the potential degrees of freedom of the aperture can be exploited, thus improving the system performance.

[0011] It is desirable to develop an antenna structure that allows for greater freedom in the design of the feed network while improving the efficiency. SUMMARY

[0012] According to a first aspect, there is provided an antenna structure comprising: a first stacked radiating structure comprising a plurality of radiators, wherein each radiator is located in a respective stacked layer; a second stacked radiating structure comprising a plurality of radiators, wherein each radiator is stacked in a respective stacked layer; a branch feed network for providing signals to the radiators, the feed network comprising a first branch for feeding one radiator of each of the first stacked radiating structure and the second stacked radiating structure and a second branch for feeding another radiator of each of the first stacked radiating structure and the second stacked radiating structure.

[0013] It turns out that the efficiency of the feeding of the antenna structure can be improved by about 10% by stacking the layers (or a combination of stacked layers) instead of feeding each complete stacked structure. Another benefit of applying this technique is that there is greater freedom in the design of the feed network, which, depending on the impedance of the radiating structures that make up the array, can result in better decoupling, greater bandwidth and lower cost.

[0014] The first branch of the feed network can be configured to feed only one (i.e. only one) of the radiators of each of the first and second stacked radiating structures. The second branch of the feed network can be configured to feed only the other (i.e. only one) of the radiators of each of the first and second stacked radiating structures. This can allow for more flexibility in configuring the feed network and improved efficiency.

[0015] The one radiator of the first stacked radiating structure can be arranged in the same stack layer as the one radiator of the second stacked radiating structure. The one radiator of the first stacked radiating structure can be arranged in a different stack layer to the one radiator of the second stacked radiating structure. This can allow for further flexibility in configuring the feed network.

[0016] The radiators of each respective stack layer of the first and second stacked radiating structures can form a layer of radiators arranged in a respective plane. This can be a spatially efficient arrangement.

[0017] The antenna structure can further comprise a planar reflector for reflecting electromagnetic radiation emitted by the plurality of radiators of the first and second stacked radiating structures. Each respective plane in which a layer of radiators is arranged can be parallel to, but offset from, the planar reflector. Arranging the radiators in parallel layers can further improve spatial efficiency.

[0018] The plurality of radiators of the first and second stacked radiating structures can have a respective common ground structure. Grounding the radiators of each structure via a common ground element can improve spatial efficiency in the antenna.

[0019] Each of the plurality of radiators of the first and second stacked radiating structures can have an independent feed point. This enables each radiator to be fed independently, for example with a respective signal phase shifted with respect to another radiator.

[0020] Each branch of the feed network can comprise one or more power dividers or phase shifters. This enables each branch to feed a plurality of radiators, if required, with amplitude and / or phase shifts between respective signals provided to respective radiators.

[0021] Each branch of the feed network can be combined at an antenna port with other branches of the feed network. This enables the radiators of the antenna structure to be fed via a common antenna port.

[0022] Each of the first and second stacked radiating structures can comprise a first radiator for emitting electromagnetic radiation having a first operational frequency band and a second radiator for emitting electromagnetic radiation having a second operational frequency band. The first and second operational frequency bands can be different. The first and second operational frequency bands can at least partially overlap. The first and second operational frequency bands can fully overlap. In some embodiments, the second operational frequency band can fully overlap the first operational frequency band, or vice versa. Such a structure can conveniently be used in an application comprising radiators that can together emit electromagnetic radiation having one or more of the frequencies 700M, 800M, 900M, 1.8G, 2.1G, 2.6G and 3.5GHz in a base station antenna or similar structure in order to support 5G. Thus, this approach can be implemented in applications where multiple radiators are required to emit different signals within different frequency bands.

[0023] The branch feed network can comprise a plurality of branches. Each branch of the feed network can comprise a proximal end and a plurality of distal ends, each distal end of a branch being connected to a respective radiator for providing a respective signal thereto. This enables each branch to feed a plurality of radiators on different stacked radiating structures in the antenna structure.

[0024] The antenna structure can comprise at least one other stacked radiating structure comprising a plurality of radiators, each stacked in a respective stacked layer. This enables the approach to be used in large antenna arrays.

[0025] The feed network can further comprise at least one other branch. Each other branch can be for feeding a respective other radiator of each of the first and second stacked radiating structures. This enables the approach to be used in antenna arrays comprising three or more stacked radiators in each radiating structure.

[0026] At least one branch of the feed network can comprise a power splitter. The power splitter can be for controlling amplitude differences between different radiators. The power splitter can be a Wilkinson power splitter or a hybrid power splitter. Other types of power splitter can be used. For example, a T-type power splitter with any particular choice of phase and amplitude distribution. This enables each branch of the feed network to provide signals to a plurality of radiators.

[0027] The plurality of radiators of the first and second stacked radiating structures can be for being fed with a phase difference between their respective signals.

[0028] At least one of the radiators of the plurality of radiators of the first and second stacked radiating structures can comprise two dipoles. The polarizations of the electromagnetic radiation emitted by the two dipoles can be orthogonal. For example, one dipole can emit vertically polarized radiation and the other horizontally polarized radiation. The polarizations of the electromagnetic radiation emitted by the two dipoles can be + / - 45 degrees.

[0029] At least some of the radiators can be planar. This can be a convenient spatial configuration enabling efficient stacking of the radiators.

[0030] The first stacked radiating structure can be adjacent to the second stacked radiating structure. This can be a spatially efficient configuration for arranging the radiating structures.

[0031] At least one of the first and second stacked radiating structures can be a basic unit for a broadside array. The antenna structure can be part of an endfire array. In a broadside array, the direction of maximum radiation is perpendicular to the axis of the array, whereas in an endfire array, the direction of maximum radiation is along the axis of the array. Thus, the present approach is applicable to a variety of antenna configurations.

[0032] The antenna structure can be a multiple input multiple output (MIMO) antenna. Thus, the antenna structure can be used in a massive MIMO based multi-user cellular communication system.

[0033] According to a second aspect, there is provided an antenna array comprising at least two antennas having the above described antenna structure. This enables the antenna structure to be combined with other such structures, for example in a row or column. BRIEF DESCRIPTION OF DRAWINGS

[0034] The present disclosure will now be described by way of example with reference to the accompanying drawings. In the drawings:

[0035] Figure 1 (a) and Figure 1 (b) show perspective and vertical cross-sectional views of an example of a stacked radiating structure;

[0036] Figure 2 An example of a known approach for feeding a stacked radiating structure is shown;

[0037] Figure 3 A known approach for feeding an array of stacked radiating structures is shown schematically;

[0038] Figure 4A known radiating structure is schematically shown in which a plurality of radiators are stacked along the z direction in order to increase the number of clusters without increasing the aperture area;

[0039] Figure 5 is a schematic diagram to help understand the terminology and structures described herein;

[0040] Figure 6 An example of an antenna array is shown;

[0041] Figure 7 Another example of an antenna array is shown;

[0042] Figure 8 Yet another example of an antenna array is shown;

[0043] Figure 9 An example of a massive MIMO antenna is shown. DETAILED DESCRIPTION

[0044] In embodiments of the disclosure, the radiators of an antenna array comprising a plurality of stacked radiating structures are fed in layers or in combination across different layers of radiators, rather than feeding the radiators of each stacked radiating structure together.

[0045] Figure 5 A schematic diagram showing some of the terminology and definitions used herein is shown. An antenna array 500 comprises a plurality of stacked radiating structures. The block at 501 shows one stacked radiating structure. The stacked radiating structure comprises a plurality of radiators 502, 503, 504. Typically, the stacked radiating structure 501 comprises n radiators. n is greater than or equal to 2. In Figure 5 In the example shown, the radiators 1502) of the structure 501 are located closest to the antenna reflector 505 in a first direction. In this preferred implementation, the first direction is perpendicular to the plane of the antenna reflector 505. The antenna reflector 505 acts as a global reflector to reflect radiation emitted by the radiators in the array. The radiators 2 (i.e. 503) are spaced apart from the radiators 1 (i.e. 502) in the first direction. The radiators n (i.e. 504) are located furthest from the antenna reflector 505 in the first direction. The radiators of each radiating structure in the same layer are preferably the same distance from the antenna reflector in the first direction. The radiators of each radiating structure are spaced apart from the other radiators in the same radiating structure in the first direction.

[0046] The radiators 506, 507 and 508 are the 1st, 2nd and nth radiators of a second radiating structure adjacent to the first radiating structure.

[0047] In this example, the radiators form layers. Layer 1, denoted by 509, includes radiators 502 and 506. Layer 2, denoted by 510, includes radiators 503 and 507. Layer n, denoted by 511, includes radiator 504 and radiator 508. In this example, the layers overlap. In other examples, the layers can partially overlap.

[0048] Each radiator of each layer can have a different impedance, and in the case of arbitrary control of the antenna array, the combination of radiators will produce a different combined impedance, resulting in potentially different bandwidth and isolation results.

[0049] In embodiments of the disclosure, the stacked radiating structures, combined from radiators, are connected to a feed network.

[0050] Each of the plurality of radiators of a stacked radiating structure preferably has an independent feed point that can enable different radiators in each stacked structure to be fed by different branches of the feed network, and if required, with a phase shift and / or amplitude difference between their respective signals.

[0051] Figure 6 A first embodiment of an antenna array 600 comprising a plurality of stacked radiating structures 601, 602, 603 is shown. Each radiating structure in the array is adjacent (i.e. sits next to) one or more other radiating structures in the array. In this example, the first radiating structure 601 is adjacent to the second radiating structure 602. The second radiating structure 602 is adjacent to the third radiating structure 603. The second radiating structure 602 sits between the first radiating structure 601 and the third radiating structure 603.

[0052] In this example, the stacked radiating structures 601, 602, 603 each comprise two radiators: a first radiator and a second radiator spaced apart from the first radiator in a first direction. The first and second radiators of structure 601 are shown at 604 and 605 respectively. The first and second radiators of structure 602 are shown at 606 and 607 respectively. The first and second radiators of structure 603 are shown at 608 and 609 respectively.

[0053] The first and second radiators of each structure 601, 602, 603 are spaced apart from an antenna reflector 610 in the first direction. In this example, the antenna reflector 610 is planar and the first direction is perpendicular to the plane of the antenna reflector. The antenna reflector 610 is used to reflect electromagnetic radiation emitted by the plurality of radiators of each of the stacked radiating structures 601, 602, 603.

[0054] In this example, each radiator in the radiating structure 601, 602, 603 is in a respective stack. Radiators 604, 606, and 608 are in stack one, and radiators 605, 607, and 609 are in stack two. In other embodiments, there can be n such stacks.

[0055] In this example, each of the radiators 604-609 is planar. For example, a planar radiator can be a dipole antenna element that includes two dipoles. The polarizations of the electromagnetic radiation emitted by the two dipoles can be orthogonal. The polarizations of the electromagnetic radiation emitted by the two dipoles can be + / - 45 degrees.

[0056] The radiators on each respective stack form a layer of radiators disposed on a respective plane. Each respective plane of radiators forms a layer that is parallel to but offset from the planar reflector 610. Radiators 604, 606, and 608 form a first layer of radiators, and radiators 605, 607, and 609 form a second layer of radiators. In other embodiments, there can be n such layers of radiators.

[0057] In this example, one of the radiators in each of the radiating structures 601, 602, 603 is used to emit electromagnetic radiation having a first operating frequency band, and another of the radiators in each of the radiating structures 601, 602, 603 is used to emit electromagnetic radiation having a second operating frequency band. The first operating frequency band and the second operating frequency band can be different. Preferably, the second operating frequency band at least partially overlaps the first operating frequency band. In some embodiments, the second operating frequency band can completely overlap the first operating frequency band, or vice versa. In the case of a partial or complete overlap of the frequency bands, an upper radiator in a stack can exhibit sufficient transparency to a first radiator to avoid interfering with its performance due to shadowing. The operating frequency bands of the radiators in the same stack (or layer) can be the same or different. For example, the six radiators in the array 600 can each emit electromagnetic radiation having a different operating frequency band to the other radiators.

[0058] Such a structure can be conveniently used to radiate at 700M, 800M, 900M, 1.8G, 2.1G, 2.6G, and 3.5GHz bands in a base station antenna or the like structure, so as to support 5G.

[0059] To provide signals to the radiators, the radiators of the radiating structure are fed through a branch feed network. The feed network can include one or more cables, conductors, or waveguides. The feed network includes a plurality of branches. Each branch is used to feed one or more radiators of the antenna structure.

[0060] In this preferred implementation, a plurality of branches are respectively used to feed a plurality of radiators of the antenna structure.

[0061] Each branch connects its respective one or more radiators to an antenna port, from which the signal is then provided to the one or more radiators. In particular, each branch connects a feed point of each of its respective one or more radiators to an antenna port. Each radiator in the antenna structure can have an independent feed point.

[0062] Each branch can comprise a plurality of arms, each arm of the respective branch being connected to a feed point of a respective radiator to which the respective branch feeds. Each branch can also comprise one or more intermediate branches for connecting the plurality of arms of the respective branch to the antenna port. Each branch can comprise one or more junctions at which one or more arms and / or one or more intermediate branches of the branch meet. Preferably, the arms and / or intermediate branches of the branch meet at a terminal junction from which a single feed line of the branch connects to the antenna port. The plurality of branches of the feed network can have the above features.

[0063] In Figure 6 the branch feed network comprises two branches, namely branches 611 and 612. Branch 611 is used to feed signals to radiators 604, 606 and 608. Branch 612 is used to feed signals to radiators 605, 607 and 609. The radiators are fed directly from the same source. The branches meet (i.e. are connected to each other) at a combined antenna port 619.

[0064] Branch 611 comprises a feed line from antenna port 619 which splits at a junction into an arm for feeding radiator 608 and an intermediate branch for feeding radiators 606 and 604. The intermediate branch splits at another junction into two arms for feeding radiators 606 and 604 respectively. Branch 612 has a similar structure: a feed line from antenna port 619 splits at a junction into an arm for feeding radiator 609 and an intermediate branch for feeding radiators 607 and 605. The intermediate branch splits at another junction into two arms for feeding radiators 607 and 605 respectively.

[0065] Each branch of the feed network therefore comprises a proximal end (the end closest to the antenna port in operation) and a plurality of distal ends. Each distal end of a branch is connected to a radiator for which it provides a signal.

[0066] In Figure 6In the illustrated example, only one radiator of each of the stacked radiating structures 601, 602, 603 is fed through a first branch of the feed network 611, and only one radiator of each of the stacked radiating structures 601, 602, 603 is fed through a second branch 612 of the feed network. The first branch 611 is used to feed the lower radiators 604, 606, 608 (closest to the reflector 610 in the first direction) of each of the stacked radiating structures. The second branch 612 is used to feed the upper radiators 605, 607, 609 (farthest from the reflector 610 in the first direction) of each of the stacked radiating structures. Thus, in this example, the radiators fed by the first branch 611 are disposed in the same stack layer, and the radiators fed by the second branch 612 are disposed in the same stack layer.

[0067] A branch of the feed network can also feed more than one radiator in a stacked radiating unit. Preferably, however, the branch does not feed all of the radiators in a stacked radiating structure.

[0068] In this preferred implementation, the radiators of each of the radiating structures 601, 602, 603 have a respective common ground structure.

[0069] As mentioned above, the radiators are directly fed by the same source. In some embodiments, however, multiple radiators of each of the stacked radiating structures 601, 602, 603 can be fed with a phase difference between their respective signals. For example, the radiators 604 and 605 of the stacked radiating structure 601 can be fed with a phase difference between their respective signals. The same is true for each of the radiating structures 602 and 603. The phase difference can be controlled by a phase shifter (digital or analog), or it can be fixed. As Figure 6 As illustrated, each branch of the feed network can also include one or more phase shifters 615 to 618.

[0070] The phase shifters can be located after the junction between the two arms, or after the junction between the arm and the intermediate branch, in order to shift the phase of the signal to a particular radiator. In Figure 6 In the illustrated example, the phase shifter 618 is used to shift the phase of the signal provided through the branch 612 with respect to the branch 611. The phase shifters 617 and 616 are used to shift the phase of the signals provided to the radiators 607 and 605, respectively, with respect to the signal provided to the radiator 609. In the branch 611, the phase shifters 614 and 615 are used to shift the phase of the signals provided to the radiators 606 and 604, respectively, with respect to the signal provided to the radiator 608.

[0071] At least one branch of the feeder network may include a power divider 613. The power divider may be a Wilkinson power divider, a hybrid power divider, or other types of power dividers. The power divider may be located at a junction between one or more arms of a corresponding branch of the feeder network or between intermediate branches. The power divider is used to control the amplitude difference of the signals supplied to different radiators. For example, power divider 613 is used to control the amplitude of the signal supplied to radiator 608 relative to the signal supplied to other radiators through branch 611.

[0072] The phase and / or amplitude difference can be arbitrarily selected between the radiators (parallel feed). In some embodiments, the phase and / or amplitude difference can be specifically selected to improve the antenna's directivity.

[0073] Therefore, in this example, radiators on the same stack layer (e.g., in the same layer) are connected together through branches of the feed network.

[0074] In other examples, for example Figure 7 In the example shown, a radiator of the first radiating structure can be placed on a different stack layer than a radiator of the second stacked radiating structure that is fed through the same branch.

[0075] Figure 7 Another implementation of array 700 is shown, in which each branch feeds alternate upper and lower radiators in stacked radiating structures 701, 702, and 703. This embodiment is an example of a two-layer array (a first layer and a second layer of radiators) in which radiators are combined by selecting different radiators from different layers.

[0076] Antenna array 700 includes stacked radiating structures 701, 702, and 703. Each radiating structure in the array is adjacent to (i.e., next to) one or more other radiating structures in the array. In this example, the first radiating structure 701 is adjacent to the second radiating structure 702. The second radiating structure 702 is adjacent to the third radiating structure 703. The second radiating structure 702 is located between the first radiating structure 701 and the third radiating structure 703.

[0077] Each stacked radiating structure 701, 702, and 703 includes two radiators: a first radiator and a second radiator spaced apart from the first radiator in a first direction. The first and second radiators of structure 701 are shown at 704 and 705, respectively. The first and second radiators of structure 702 are shown at 706 and 707, respectively. The first and second radiators of structure 703 are shown at 708 and 709, respectively. The first and second radiators of structures 701, 702, and 703 are all spaced apart from the antenna reflector 710 in the first direction.

[0078] Each radiator in the radiating structure 701, 702, 703 is in a respective stack. Radiator 704, radiator 706 and radiator 708 are in stack one, and radiator 705, radiator 707 and radiator 709 are in stack two. In other embodiments, there can be n such stacks.

[0079] As in the example above, each of the radiators 704 to 709 is planar.

[0080] The radiators on each respective stack form a layer of radiators disposed on a respective plane. Each respective plane of radiators forms a layer parallel to but offset from the planar reflector 710. Radiators 704, 706 and 708 form a first layer of radiators, and radiators 705, 707 and 709 form a second layer of radiators. In other embodiments, there can be n such layers of radiators.

[0081] Each radiator can emit electromagnetic radiation in a particular operating frequency band, as described above in relation to the embodiments of Figure 6 In this example, one radiator of each of the radiating structures 701, 702, 703 is used to emit electromagnetic radiation having a first operating frequency band, and another radiator of each of the radiating structures 701, 702, 703 is used to emit electromagnetic radiation having a second operating frequency band. The first operating frequency band and the second operating frequency band can be different. Preferably, the second operating frequency band at least partially overlaps the first operating frequency band. In some embodiments, the second operating frequency band can completely overlap the first operating frequency band, or vice versa. The operating frequency bands of the radiators in the same stack (or layer) can be the same or different.

[0082] In this example, each branch of the feed network is used to feed one radiator of each radiating structure.

[0083] In Figure 7 the branch feed network comprises two branches 711 and 712. Branch 711 is used to feed signals to radiators 704, 707 and 708. Branch 712 is used to feed signals to radiators 705, 706 and 709. The radiators are fed directly by the same source. The branches meet (i.e. are connected to each other) at the combined antenna port 719. The branches can have arms, intermediate branches and junctions, as described above in relation to the embodiments of Figure 6

[0084] ​Branch 711 comprises a feed line from antenna port 719 which at a junction divides into an arm for feeding radiator 708 and an intermediate branch for feeding radiators 707 and 704. The intermediate branch at a further junction divides into two arms for feeding radiators 707 and 704 respectively. Branch 712 has a similar structure: a feed line from antenna port 719 which at a junction divides into an arm for feeding radiator 709 and an intermediate branch for feeding radiators 706 and 705. The intermediate branch at a further junction divides into two arms for feeding radiator 706 and radiator 705 respectively.

[0085] Thus, each branch of the feed network comprises a proximal end and a plurality of distal ends. Each distal end of a branch is connected to a radiator for which it provides a signal.

[0086] In this example, only one radiator of each of the stacked radiating structures 701, 702, 703 is fed by first branch 711 of the feed network, and only one radiator of each of the stacked radiating structures 701, 702, 703 is fed by second branch 712 of the feed network. First branch 711 is for feeding alternate lower radiators 704, upper radiators 707, lower radiators 708 of each of the stacked radiating structures 701, 702, 703. Second branch 712 is for feeding alternate upper radiators 705, lower radiators 706, upper radiators 709 of each of the stacked radiating structures 701, 702, 703. Thus, in this example, the radiators fed by each branch are disposed in alternate stacked layers (i.e. each branch does not feed all the radiators in the same stacked layer or layers).

[0087] A branch of the feed network can also feed more than one radiator in a stacked radiating unit. However, preferably, the branch does not feed all the radiators in a stacked radiating structure.

[0088] In this preferred implementation, the radiators of each of the radiating structures 701, 702, 703 have a respective common ground structure.

[0089] The feed network can comprise power dividers and phase shifters which can operate as previously described in relation to the example of Figure 6 .

[0090] In Figure 7In this configuration, phase shifter 718 is used to shift the phase of the signal provided through branch 712 relative to branch 711. Phase shifters 717 and 716 are used to shift the phase of the signals provided to radiators 706 and 705, respectively, relative to the signals provided to radiator 709. In branch 711, phase shifters 714 and 715 are used to shift the phase of the signals provided to radiators 707 and 704, respectively, relative to the signals provided to radiator 708.

[0091] This method can be extended to combinations of #n layers and #m radiators, where both n and m are greater than 1.

[0092] Figure 8 This illustrates a two-column stacked radial structure. Each column has a structure similar to... Figure 7 The array 700 described above has the same structure. In this example, the antenna reflector 710 is common to both columns. This design can be used to integrate massively multiple input multiple output (mMIMO) antennas with different passive antenna arrays.

[0093] Figure 9 An example of an mMIMO antenna 900 comprising multiple stacked radiating structures 901 to 908 is shown. Structures 901 to 908 share a global antenna reflector 915. Radiators are connected to radiators on different or the same layer via branches 909, 910, 911, and 912 of the feed network to gain additional degrees of freedom. In this example, each branch does not feed more than one radiator in a given stacked radiating structure. As described in the example above, the feed network may also include various phase shifters, such as those indicated at 913 and 914, and power dividers.

[0094] exist Figures 6 to 9 In the example shown, the antenna structure includes two layers of radiators in each radiating structure. However, the antenna structure may include yet another layer of radiators. The feed network may also include one or more additional branches. Each branch can be used to feed corresponding additional radiators in one or more other layers. The upper layer preferably exhibits sufficient transparency to the lower layer to avoid interference with its performance due to shading. This can be achieved using various known methods.

[0095] Therefore, the stacked radiators of the antenna array are fed layer by layer (or a combination of layers), rather than using a branch of the feeding network to feed each radiator individually. Radiators in one layer are connected to radiators in the same or different layers via the feeding network, but not to radiators in the stack.

[0096] This method of feeding the radiators has been simulated and has proven to be beneficial in certain scenarios (compared to other conventional cluster distributions). It has been proven that feeding through a layer instead of a stacked structure can improve the efficiency by 10%.

[0097] Another benefit of applying this technique is that there is more freedom in designing the feed network, which, depending on the impedance of the radiating structures that make up the array, can result in better decoupling, larger bandwidth and lower cost.

[0098] The antenna structure can be an end-fire array of radiators. At least one of the stacked radiating structures can be used as a building block for a broadside array (e.g. in a base station antenna array). The antenna structure can be a multiple-input multiple-output antenna.

[0099] This antenna configuration can be used in a range of devices, such as a mobile phone, a base station, a radar or an antenna mounted on an aircraft. In particular, but not exclusively, the concept can be applied in a multi-user cellular communication system based on massive MIMO.

[0100] The applicant hereby discloses separately each and every feature described herein and any combination of two or more such features. In view of the foregoing description, those of ordinary skill in the art will be able to devise numerous ways to implement the application without departing from the scope of the application. Accordingly, the disclosure is not limited to the specific embodiments described herein, but includes all alternatives falling within the scope of the claims. The various aspects of the disclosure can include any of the individual features described herein, or any combination of two or more such features. In view of the foregoing description, those of ordinary skill in the art will be able to devise numerous ways to implement the application without departing from the scope of the application. Accordingly, the disclosure is not limited to the specific embodiments described herein, but includes all alternatives falling within the scope of the claims.

Claims

1. An antenna structure (600, 700, 800, 900), characterized by comprises a plurality of radiators (604, 605, 704, 705), each radiator being located at a respective stack layer; comprises a plurality of radiators (606, 607, 706, 707), each radiator being stacked at a respective stack layer; a branch feed network (611, 612, 711, 712, 909, 910) for providing signals to the radiators (604, 605, 606, 607, 704, 705, 706, 707), the feed network comprising a first branch (611, 711, 909) for feeding one radiator (604, 606, 704, 707) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702) and a second branch (612, 712, 910) for feeding another radiator (605, 607, 705, 706) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702); wherein the one radiator (704) of the first stacked radiating structure (701) and the one radiator (707) of the second stacked radiating structure (702) are arranged at different stack layers. the first branch (611, 711) of the feed network is for feeding only the one radiator (604, 606, 704, 707) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702).

2. The antenna structure (600, 700, 800, 900) of claim 1, characterized by the second branch (612, 712) of the feed network is for feeding only the other radiator (605, 607, 705, 706) of each of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702).

3. The antenna structure (600, 700, 800, 900) according to claim 1 or 2, characterized in that, the radiators at each respective stack layer of the first stacked radiating structure (601, 701) and the second stacked radiating structure (602, 702) form a layer of radiators arranged in a respective plane.

4. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized in that, the antenna structure further comprises a planar reflector (610, 710, 915) for reflecting electromagnetic radiation emitted by the plurality of radiators (604, 605, 606, 607, 704, 705, 706, 707) of the first stacked radiating structure and the second stacked radiating structure, wherein each respective plane is parallel to the planar reflector but offset from the planar reflector.

5. The antenna structure (600, 700, 800, 900) of claim 4, characterized by the plurality of radiators (604, 605, 606, 607, 704, 705, 706, 707) of the first stacked radiating structure and the second stacked radiating structure have a respective common ground structure.

6. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized in that, ​ 7. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by Each of the plurality of radiators of the first and second stacked radiating structures has an independent feed point.

8. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by Each branch (611, 612, 711, 712) of the feed network comprises one or more phase shifters (614, 615, 616, 617, 618, 714, 715, 716, 717, 718, 913, 914).

9. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by Each branch (611, 612, 711, 712) of the feed network is combined at an antenna port (619, 719) with other branches of the feed network.

10. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by Each of the first (601, 701) and second (602, 702) stacked radiating structures comprises a first radiator (604, 606, 704, 706) for emitting electromagnetic radiation having a first operational frequency band and a second radiator (605, 607, 705, 707) for emitting electromagnetic radiation having a second operational frequency band.

11. The antenna structure (600, 700, 800, 900) of claim 10, characterized by The first and second operational frequency bands at least partially overlap.

12. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by The antenna structure comprises at least one further stacked radiating structure comprising a plurality of radiators, each stacked in a respective stack layer.

13. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by The feed network further comprises at least one further branch, each for feeding respective further radiators of each of the first and second stacked radiating structures.

14. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by At least one branch (611, 612, 711, 712) of the feed network comprises a power divider (613, 713) which is a Wilkinson power divider or a hybrid power divider.

15. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by The plurality of radiators (604, 605, 606, 607, 704, 705, 706, 707) of the first (601, 701) and second (602, 702) stacked radiating structures are for being fed with a phase difference between respective signals of the plurality of radiators (604, 605, 606, 607, 704, 705, 706, 707).

16. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by At least one of the plurality of radiators (604, 605, 606, 607, 704, 705, 706, 707) of the first (601, 701) and second (602, 702) stacked radiating structures comprises two dipoles, wherein polarizations of electromagnetic radiation emitted by the two dipoles are orthogonal.

17. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by At least some of the radiators (604, 605, 606, 607, 704, 705, 706, 707) are planar.

18. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by The first (601, 701) stacked radiating structure is adjacent to the second (602, 702) stacked radiating structure.

19. The antenna structure (600, 700, 800, 900) according to any of the preceding claims, characterized by At least one of the first (601, 701) and second (602, 702) stacked radiating structures is a basic unit of a broadside array.

20. The antenna structure (600, 700, 800, 900) according to any one of claims 1 to 18, characterized by, The antenna structure is part of an endfire array.

21. The antenna structure (900) according to any one of the preceding claims, characterized in that, The antenna structure is a multiple-input multiple-output antenna (900).

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