Base station antenna with complementary frequency selective surface structure

Abstract

The invention relates to a base station antenna with a complementary frequency selective surface structure. A base station antenna includes a supplemental FSS structure having a metal mesh layer and a printed circuit board layer, the metal mesh layer and the printed circuit board layer being stacked in a front-rear direction and aligned in a longitudinal direction. The supplemental FSS structure is located between the first FSS layer and the primary reflector in the longitudinal direction. The supplemental FSS structure reflects and / or blocks RF energy from one of the low-band radiating elements or the middle-band radiating elements, and transfers RF energy from the array of mMIMO radiating elements in a higher frequency band than the low-band radiating elements and the middle-band radiating elements.

Description

BACKGROUND

[0001] The present invention relates generally to radio communication, and more specifically to base station antennas for cellular communication systems.

[0002] Cellular communication systems are well known in the art. In a cellular communication system, a geographic region is divided into a series of areas, called "cells," that are served by corresponding base stations. A base station can include one or more antennas that are configured to provide bidirectional radio frequency ("RF") communication with mobile users within the cell served by the base station. In many cases, each cell is divided into "sectors." In one common configuration, a hexagonal-shaped cell is divided into three 120° sectors in an azimuthal plane, and each sector is served by one or more base station antennas having an approximately 65° azimuthal half-power beamwidth (HPBW). Typically, the base station antennas are mounted on a tower or other elevated structure, with a radiation pattern (also referred to herein as an "antenna beam") generated by the outwardly pointing base station antennas. Base station antennas are typically implemented as linear or planar phased arrays of radiating elements.

[0003] To accommodate increasing cellular traffic, cellular operators have added cellular service in various new frequency bands. To increase capacity without further increasing the number of base station antennas, multi-band base station antennas have been introduced that include multiple linear arrays of radiating elements. In addition, base station antennas are now being deployed that include "beamforming" arrays that include multiple columns of radiating elements. The radios for these beamforming arrays can be integrated into the antenna, such that the antenna can perform active beamforming (i.e., the shape of the antenna beam generated by the antenna can be adaptively changed to improve the performance of the antenna). These beamforming arrays typically operate in higher frequency bands, such as various portions of the 3.3-5.8 GHz band. Antennas with integrated radios that can adjust the amplitude and / or phase of sub-components of RF signals transmitted through individual radiating elements or small groups thereof are referred to as "active antennas." Active antennas can generate narrow beamwidth, high gain antenna beams by changing the amplitude and / or phase of sub-components of RF signals transmitted through the antenna, and can steer the generated antenna beam in different directions.

[0004] With the development of wireless communication technology, integrated base station antennas have emerged that include passive modules and active antenna modules with active antennas. Passive modules can include one or more passive arrays of radiating elements that are configured to generate a relatively static antenna beam, such as an antenna beam configured to cover a 120-degree sector (in an azimuth plane) of the base station antenna. The passive arrays can include arrays that operate according to second generation (2G), third generation (3G), or fourth generation (4G) cellular standards. These passive arrays are not configured to perform active beamforming operations, but they often have remote electronic tilt (RET) capability, which allows the shape of the antenna beam to be changed by electromechanical means in order to change the coverage area of the antenna beam. Active antenna modules can include one or more arrays of radiating elements that operate according to fifth generation (or later) cellular standards. These arrays often have individual amplitude and phase control of subsets of the radiating elements therein, and perform active beamforming.

[0005] FIGS. 1 and 2 show an example of a prior art base station antenna 10 that includes a pair of beamforming arrays and associated beamforming radios. When the antenna 10 is installed for normal operation, the base station antenna 10 is typically installed with a longitudinal axis L of the antenna 10 extending along a vertical axis (e.g., the longitudinal axis L can be generally perpendicular to a plane defined by the horizon). The front face of the antenna 10 is installed opposite a tower or other mounting structure, pointing toward the coverage area of the antenna 10. The antenna 10 includes a radome 11 and a top end cap 20. The antenna 10 also includes a bottom end cap 30 that includes a plurality of connectors 40 mounted therein. As shown, the radome 11, top cap 20, and bottom cap 30 define an outer housing 10h of the antenna 10. Antenna assemblies are housed within the housing 10h.

[0006] FIG. 2 illustrates that the antenna 10 can include one or more radios 50 mounted to the housing 10h. Further details of an example conventional base station antenna can be found in co-pending WO 2019 / 236203 and WO 2020 / 072880, the contents of which are incorporated by reference as if recited in full herein.

[0007] Base station antennas that include active antenna units with radios and mMIMO arrays of radiating elements located behind the back of the base station antenna are also disclosed. See U.S. Patent No. 11,482,774, the contents of which are incorporated by reference as if recited in full herein. SUMMARY

[0008] Embodiments of the invention relate to a base station antenna having a supplemental frequency selective surface (FSS) structure located between (in the longitudinal direction) a first frequency selective surface (FSS) and a main reflector. The supplemental FSS structure has a shorter length (in the longitudinal direction) than the first FSS and the main reflector.

[0009] The low band radiating elements and the mid band radiating elements can be arranged to protrude forward of the supplemental FSS structure, the supplemental FSS structure having a feed plate for coupling to at least some of the radiating elements of the supplemental FSS structure.

[0010] The supplemental FSS structure can be parallel to the main reflector and the first FSS, generally aligned with one or both of the main reflector and the first FSS in the front-to-back direction of the base station antenna to at least partially lie in a common longitudinally extending plane.

[0011] The supplemental FSS structure can be provided as a mesh layer and a cooperating printed circuit board layer stacked in the front-to-back direction. Alternatively, the supplemental FSS structure can be provided as a mesh layer which can cooperate with a portion of the first FSS such that the mesh layer overlaps the first FSS layer and can lie forward of it in the front-to-back direction.

[0012] The mesh layer can lie forward of the PCB FSS layer and / or the first FSS.

[0013] The supplemental FSS structure can reflect or block low band signals and mid band signals from respective low band radiating elements and mid band radiating elements, and pass higher band signals from higher band radiating elements behind the supplemental FSS.

[0014] The supplemental FSS structure can be configured to allow the high band radiating elements to propagate electromagnetic waves therethrough, and to reflect low band signals from low band radiating elements forward of the supplemental FSS structure.

[0015] The supplemental FSS structure can have a metal mesh layer having feed plate apertures. Feed plates can be mounted to the metal mesh layer to extend across respective feed plate apertures. One or more feed stalks can be mounted to protrude forward and rearward of the feed plates and the metal mesh layer.

[0016] The supplemental FSS structure can be provided with a metal mesh layer having a respective array of unit cells and feed stalks protruding forward of the metal mesh layer.

[0017] The supplemental FSS structure can comprise a printed circuit board having an array of unit cells definable by conductive patches. The array or unit cells can be provided in a different pattern to the pattern of the array of unit cells of the metal mesh layer.

[0018] The printed circuit board can be configured to block or reflect the low-band signals and the mid-band signals from the respective low-band radiating elements and the mid-band radiating elements, and the metal mesh layer can be configured to block and / or reflect the low-band signals and the mid-band signals from the respective low-band radiating elements and the mid-band radiating elements.

[0019] Embodiments of the present invention relate to a base station antenna comprising: a first frequency selective surface (FSS); a main reflector; and a supplemental frequency selective surface (FSS) structure located between the first FSS and the main reflector in a longitudinal direction.

[0020] The supplemental FSS structure can comprise a metal mesh layer having an array of unit cells and a printed circuit board layer having an array of unit cells. The metal mesh layer and the printed circuit board layer can be aligned to be located in a substantially common footprint in the longitudinal direction and stacked in an anterior-posterior direction of the base station antenna.

[0021] The metal mesh layer can be located anterior to the printed circuit board layer.

[0022] The base station antenna can further comprise a pair of laterally spaced apart and longitudinally extending rails. The supplemental FSS structure can laterally extend between the rails and can be attached to the rails.

[0023] The supplemental FSS structure has a length, the main reflector has a length, and the first FSS has a length, all in a longitudinal direction of the base station antenna. The length of at least one layer of the supplemental FSS can be in the range of 10-30% of the length of the first FSS and / or the main reflector.

[0024] The supplemental FSS structure can be parallel to the first FSS and the main reflector.

[0025] At least a portion of the supplemental FSS structure can be located in a common plane with the first FSS.

[0026] At least a portion of the supplemental FSS structure can be located in a plane anterior to the first FSS.

[0027] The supplemental FSS structure can comprise a metal mesh layer having an array of unit cells, the array of unit cells being located in a plane anterior to a plane of the first FSS and can have a longitudinal extent located only along a portion of the first FSS or be configured to not overlap the first FSS.

[0028] The base station antenna can further comprise a feed plate coupled to the metal mesh layer, and the feed plate can be configured to replicate at least a portion of a unit cell shape of the unit cells in the array of unit cells.

[0029] The supplemental FSS structure can include a metallic mesh layer having at least one feed panel aperture and an array of unit cells. The feed panel can extend across and overlap a portion of the array of unit cells surrounding the feed panel aperture.

[0030] The feed panel can have a metallic shape that replicates at least a portion of a shape of a unit cell structure of one or more unit cells of the array of unit cells, and the metallic shape can overlap at least some of the array of unit cells.

[0031] The base station antenna can further include a first linear array of first radiating elements and a second linear array of second radiating elements. A single one of the first linear array of first radiating elements and a single one of the second linear array of second radiating elements can protrude forward from the supplemental FSS structure.

[0032] The base station antenna can further include a plurality of columns of second radiating elements laterally spaced apart. Only two rows in each of the plurality of columns of second radiating elements can protrude forward from the supplemental FSS structure.

[0033] The base station antenna can further include a bracket laterally extending between a pair of longitudinally extending rails, and the bracket can be attached to a bottom portion of the supplemental FSS structure and to the main reflector.

[0034] The bracket can have a U-shape, with arms of the U-shape facing down over the main reflector.

[0035] A closed laterally extending end of the U-shape can be attached to the supplemental FSS structure, and a first FSS can be attached to a top portion of the supplemental FSS structure.

[0036] The metallic mesh layer has sidewalls that can be angled outward from a main planar body thereof in a forward direction, and a printed circuit board layer of the supplemental FSS structure can terminate laterally inward from the sidewalls of the metallic mesh layer.

[0037] The sidewalls can have an array of unit cells arranged in a repeating pattern along a length of the supplemental FSS structure.

[0038] The array of unit cells of the metallic mesh layer can be arranged in a first pattern that extends behind the first linear array and the second linear array of first radiating elements, behind the plurality of columns of second radiating elements, and in front of the plurality of array of third radiating elements across at least a majority of a lateral dimension of the base station antenna.

[0039] The supplemental FSS structure can reflect and / or block energy in a first operational frequency band of first radiating elements of the base station antenna and a second operational frequency band of second radiating elements of the base station antenna. The second frequency band can include frequencies higher than the first frequency band, and the supplemental FSS structure can allow energy from the mMIMO array of radiating elements in a third operational frequency band to propagate therethrough. The third operational frequency band can include frequencies higher than the second frequency band. At least some of the mMIMO array of radiating elements can be positioned behind the supplemental FSS structure.

[0040] The base station antenna can include active antenna elements positioned behind a rear of a housing that encloses the first FSS, the supplemental FSS structure, and the primary reflector.

[0041] The supplemental FSS structure can be configured to allow RF energy in at least a portion of a 3.2-4.1 GHz frequency band to propagate therethrough.

[0042] The base station antenna can further include a plurality of feed plates coupled to the supplemental FSS structure. At least some of the plurality of feed plates can have a lattice body having an aperture surrounded by linear segments that define at least a first conductive signal trace and a second conductive signal trace. The first conductive signal trace and the second conductive signal trace can extend downwardly over the primary reflector.

[0043] At least some of the linear segments of the feed plates can be aligned with the metal linear segments of the metal mesh layer.

[0044] At least some of the linear segments of the feed plates can extend downwardly over the primary reflector.

[0045] The first FSS can terminate above the supplemental FSS structure.

[0046] The metal mesh layer can be configured to block and / or reflect RF energy from the mid-band radiating elements, and the printed circuit board layer can be configured to block and / or reflect RF energy from the low-band radiating elements.

[0047] The metal mesh layer can be configured to block and / or reflect RF energy from the low-band radiating elements, and the printed circuit board layer can be configured to block and / or reflect RF energy from the mid-band radiating elements.

[0048] The metal mesh layer can be configured to block and / or reflect RF energy from the low-band radiating elements and the mid-band radiating elements, and the printed circuit board layer can be configured to block and / or reflect RF energy from the low-band radiating elements and the mid-band radiating elements.

[0049] Still other aspects of the application relate to a base station antenna comprising: a reflector; a first frequency selective surface (FSS); an array of first frequency band radiating elements all coupled to a first radio frequency (RF) input, wherein a first subset of the first frequency band radiating elements overlap the reflector in a forward direction perpendicular to a plane defined by a major surface of the reflector, and a second subset of the first frequency band radiating elements overlap the first FSS in the forward direction; and a supplemental frequency selective surface (FSS) structure that overlaps at least one of the first FSS and the second subset of the first frequency band radiating elements in the forward direction, but does not overlap all of the second subset of the first frequency band radiating elements in the forward direction.

[0050] The base station antenna can further include an array of second frequency band radiating elements all coupled to a second RF input, wherein a first subset of the second frequency band radiating elements overlap the reflector in the forward direction, and a second subset of the second frequency band radiating elements overlap both the first FSS and the supplemental FSS in the forward direction. The second frequency band can contain higher frequencies than the first frequency band.

[0051] The supplemental FSS can be configured to reflect RF energy in an operating frequency band of the array of second frequency band radiating elements.

[0052] None of the second frequency band radiating elements overlap the first FSS.

[0053] None of the second frequency band elements protrude forward from the first FSS, and only some of the second frequency band radiating elements protrude forward from the supplemental FSS.

[0054] It should be noted that aspects of the disclosure described with respect to one embodiment can be included in other different embodiments, even if they are not specifically described with respect to other different embodiments. In other words, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless they are mutually exclusive. BRIEF DESCRIPTION OF DRAWINGS

[0055] FIG. 1 is a perspective view of a prior art base station antenna.

[0056] FIG. 2 is a rear view of another prior art base station antenna.

[0057] Figure 3 is a rear perspective view of an exemplary base station antenna coupled to an active antenna module according to an embodiment of the application.

[0058] Figure 4 is a front view of a portion of a base station antenna.

[0059] Figure 5Ais a front view of a portion of a base station antenna including a supplemental FSS structure according to embodiments of the application.

[0060] Figure 5B is Figure 5A is a side view of a portion of a base station antenna shown in

[0061] Figure 5C is Figure 5B is a side view of a portion of a base station antenna shown in

[0062] Figure 6 is Figure 4 is a back view of a portion of a base station antenna shown in

[0063] Figure 7 is a back view of a portion of a base station antenna shown in Figure 5A

[0064] Figure 8 is a simplified side schematic cross-sectional view of a portion of a base station antenna according to embodiments of the application showing a supplemental FSS structure in front of components of an active antenna module.

[0065] Figure 9 is a simplified schematic side view of a portion of a base station antenna according to embodiments of the application showing a supplemental FSS structure in front of an active antenna module.

[0066] Figure 10 is a front view of an exemplary array of radiating elements of an active antenna module according to embodiments of the application.

[0067] Figure 11 is a simplified schematic exploded view of a portion of a base station antenna according to embodiments of the application showing an exemplary unit cell shape of a supplemental FSS structure.

[0068] Figure 12A is a magnified view of a portion of an exemplary grid layer of a supplemental FSS structure according to embodiments of the application.

[0069] Figure 12B is a magnified view of an exemplary feed plate with feed stalks according to embodiments of the application.

[0070] Figure 12C is a magnified view of a portion of a grid layer and a feed plate shown in Figure 12A and 12B is an assembled view of a portion of a grid layer and a feed plate shown in ​

[0071] Figure 13 is a back view of a portion of a grid layer including a radiating element and a feed plate according to an embodiment of the application.

[0072] Figure 14 is a back view of another embodiment of a portion of a grid layer including a radiating element according to an embodiment of the application.

[0073] Figure 15 is a back view of another embodiment of a portion of a grid layer including a radiating element according to an embodiment of the application.

[0074] Figure 16 is a front view of a grid layer and a feed plate according to an embodiment of the application. Figure 15

[0075] Figure 17A is an enlarged front perspective view of another embodiment of a portion of a grid layer including a feed plate having a back conductive layer and a radiating element according to an embodiment of the application.

[0076] Figure 17B is an enlarged front perspective view of another embodiment of a portion of a grid layer including a feed plate having a front conductive layer and a radiating element according to an embodiment of the application.

[0077] Figure 18 is a side perspective view of an example feed plate.

[0078] Figure 19 is an enlarged back view of a portion of a grid layer and a feed plate having a feed stem according to an embodiment of the application. DETAILED DESCRIPTION

[0079] Figure 3 A base station antenna 100 according to certain embodiments of the application is shown. In the following description, the base station antenna 100 will be described using terminology that assumes the base station antenna 100 is mounted for use on a tower, pole, or other mounting structure, with the longitudinal axis L of the base station antenna 100 extending along a vertical axis, the front of the base station antenna 100 being mounted opposite the tower, pole, or other mounting structure pointing toward the target coverage area of the base station antenna 100, and the back 100r of the base station antenna 100 facing the tower or other mounting structure. It will be understood that the base station antenna 100 can not always be mounted such that its longitudinal axis L extends along a vertical axis. For example, the base station antenna 100 can be tilted slightly (e.g., less than 10°) relative to the vertical axis, such that the resulting antenna beams formed by the base station antenna 100 each have a small mechanical downtilt.

[0080] ​The base station antenna 100 can be coupled to or include at least one active antenna module 110. The term “active antenna module” is used interchangeably with “active antenna unit” and “AAU” and “active antenna” and refers to a cellular communication unit that includes radio circuitry and associated radiating elements. The radio circuitry is capable of electronically adjusting the amplitude and / or phase of sub-components of RF signals output to different radiating elements of the array or groups thereof. The active antenna module 110 includes radio circuitry and radiating elements (e.g., a multiple-input multiple-output (mMIMO) beamforming antenna array) and can include other components such as filters, calibration networks, antenna interface signal group (AISG) controllers, etc. The active antenna module 110 can be provided as a single integrated unit or as a plurality of stackable units including, for example, a first sub-unit and a second sub-unit (e.g., a radio sub-unit (box) having radio circuitry and an antenna sub-unit (box) having a multi-column array of radiating elements) and the first and second sub-units are stackably attached together in a front-to-back direction of the base station antenna 100 with the radiating elements 1195 of the antenna assembly 1190 of the AAU 110 closer to a front radome 111f of the housing 100h of the base station antenna 100 / radome 111 of the base station antenna than the radio circuitry sub-unit 1120 Figure 8 , 9 ) In some embodiments, the radiating elements 1195 can include a sub-unit separate from the radio circuitry and the radiating element sub-unit can be mounted within the base station antenna 100 rather than outside the base station antenna 100.

[0081] The base station antenna 100 has a housing 100h. The housing 100h can be substantially rectangular with a flat rectangular cross-section. The housing 100h can be provided to define at least a portion of the radome 111 with at least the front side 111f configured as a dielectric cover that allows RF energy to pass through in certain frequency bands. The housing 100h can also be configured such that the rear portion 100r defines a rear side 111r radome opposite the front side radome 111f. Optionally, the housing 100h and / or the radome 111 can further include two (narrow) side walls 100s, 111s that face each other and extend rearward between the front side 111f and the rear side 111r. Typically, the top side 100t of the housing 100h can be sealed in a weatherproof manner and can include an end cap 120 and the bottom 100b of the housing 100h can be sealed with a separate end cap 130. At least a portion of the front side 111f, the side walls 111s, and typically the rear side 111r of the radome 111 is substantially transparent to radio frequency (RF) energy within the operating frequency bands of the base station antenna 100 and the active antenna module 110. The radome 111 can be formed of, for example, fiberglass or plastic.

[0082] Still referring to Figure 3In some embodiments, the active antenna module 110 can be attached to the base station antenna 100 using the frame 112 and accessory mounting brackets 113, 114. The rear portion 111r of the housing 100h can be a flat surface extending along a common plane over its entire longitudinal extent or extending along at least a portion of its longitudinal extent.

[0083] The base station antenna 100 includes an antenna assembly 190, which may be referred to as a "passive antenna assembly." The term "passive antenna assembly" refers to an antenna assembly having arrays of radiating elements, each array of which is coupled to a radio device external to the antenna, typically a remote radio head mounted adjacent to the base station antenna 100. The arrays of radiating elements included in the passive antenna assembly 190 (…) Figure 4 , 5A The passive antenna assembly 190 is configured to form static antenna bundles (e.g., each configured to cover a sector of the base station). The passive antenna assembly 190 may include a main reflector 214, some of which have radiating elements protruding in front of the main reflector, and the radiating elements may include one or more linear arrays 220-1, 220-2 of low-frequency band radiating elements operating in all or part of the 617-960 MHz frequency band and / or one or more linear arrays 230-1, 230-2 of mid-frequency band radiating elements operating in all or part of the 1427-2690 MHz frequency band. The passive antenna assembly 190 is mounted within the housing 100h of the base station antenna 100, and one or more active antenna modules 110 may be releasably (detachably) coupled (e.g., directly or indirectly attached) to the housing 100h of the base station antenna 100.

[0084] refer to Figure 3 In another embodiment, the rear surface 100r may include a plurality of longitudinally spaced mounting structure brackets extending rearward from the housing 100h, shown as an upper bracket 115, a middle bracket 116, and a lower bracket 117, respectively. In some embodiments, the mounting structure brackets 115, 116, and 117 may be configured to be attached to one or more mounting structures, such as towers, poles, or buildings (not shown). At least two of the mounting structure brackets 115 and 116 may also be configured to be attached to a frame 112 of the base station antenna assembly in use. The frame 112 may extend over a sub-length of the longitudinal range L of the base station antenna 100, wherein the sub-length is within Figure 3 The frame 112 is shown as at least its main portion (at least 50% of its length). The frame 112 may include a top 112t, a bottom 112b, and two opposing long sides 112 extending between the top 112t and the bottom 112b. The frame 112 may have an open central space 112c extending laterally between the sides 112s and longitudinally between the top 112t and the bottom 112b.

[0085] In use, the frame 112 can be configured such that various different active antenna modules 110 can be installed to the frame 112 using appropriate fittings to mount the brackets 113, 114. Thus, various active antenna modules 110 can be interchangeably attached to the same base station antenna 100. Although the frame 112 is shown by way of example, other mounting systems can be used.

[0086] In some embodiments, multiple active antenna modules 110 can be simultaneously attached to the same base station antenna 100 at different longitudinal positions using one or more frames 112. Such active antenna modules 110 can have different sizes, e.g., different lengths and / or different widths and / or different thicknesses.

[0087] Referring to Figure 4 and 6 , an exemplary passive antenna 190 is shown that includes a main reflector 214 for the base station antenna 100. As shown, the main reflector 214 is located below (in the longitudinal direction) a first frequency selective surface (FSS) 170 that extends above the main reflector 214.

[0088] Turning now to Figure 5A , 5B and 7, the base station antenna 100’ with the passive antenna 190 can have a supplemental FSS structure 1000 located between (in the longitudinal direction) the first FSS 170 and the main reflector 214, as compared to the passive antenna 190 shown in Figure 4 and 6 . The first FSS 170 can have a length “dl”, the supplemental FSS structure 1000 can have a length “d2”, and the main reflector 214 can have a length “d3”. As shown, d2 is less than dl and d3. In some embodiments, the length d2 of the supplemental FSS structure 1000 can be in the range of 10-30% of the length dl of the first FSS 170 and / or the length d3 of the main reflector 214. However, d2 can have other lengths and is not limited to these exemplary lengths.

[0089] Referring to Figure 5A , the coupling segments 175 can optionally extend laterally between the rails 128 and can be used to attach a bottom portion of the first FSS 170 to a top portion of the supplemental FSS structure 1000. The coupling segments 175 can be metal or plastic or a combination thereof.

[0090] Referring to Figure 7The first FSS 170 can be provided as a metal mesh layer or a printed circuit board having an array 170a of unit cells 170u configured to block and / or reflect RF energy from the low-band radiating elements 222 of the linear arrays 220-1, 220-2 of radiating elements 222. In some embodiments, the first FSS 170 is provided as a printed circuit board having an array 170a of unit cells 170u.

[0091] The first FSS 170 can terminate adjacent a top portion of the supplemental FSS structure 1000.

[0092] The first FSS 170 can extend behind and partially overlap the supplemental FSS structure 1000 in the longitudinal direction.

[0093] At least a portion of the supplemental FSS structure 1000, 1000' can be located in a plane forward of the plane of the first FSS 170, respectively, and can have a longitudinal extent located only along a portion of the first FSS 170 (e.g., a bottom portion of the first FSS 170, as shown in Figure 5B 5C ) or can be configured to be located entirely (longitudinally) below and not overlapping the first FSS 170 ( Figure 5C ). Figure 5B

[0094] The supplemental FSS structure 1000 can include a metal mesh layer 172 including an array 172a of unit cells 172u and a printed circuit board layer 1172 including an array 1172a of unit cells 1172u ( Figure 7-9

[0095] Referring to Figure 5A 5B , 8 and 9, the metal mesh layer 172 can be located forward of the printed circuit board layer 1172. The metal mesh layer 172 can have the same length as the printed circuit board layer 1172. The metal mesh layer 172 can have a greater lateral extent than the printed circuit board layer 1172. In other embodiments, the positions of the metal mesh layer 172 and the printed circuit board layer 1172 can be reversed, such that the printed circuit board layer 1172 is located forward of the metal mesh layer 172.

[0096] ​​​​The metal mesh layer 172 can have sidewalls 172w that angle outward from the plane of the body 172b of the metal mesh layer 172 in the forward direction. The sidewalls 172w can have a pattern of unit cells 172u extending along their length. The printed circuit board layer 1172 can terminate laterally inward from the sidewalls 172w of the metal mesh layer 172.

[0097] Referring to Figure 5B , the supplemental FSS structure 1000 can be located a distance d4 forward of the first FSS 170. Support legs 1179 can extend rearward of the FSS structure 1000. Attachment members 1180 can couple the metal mesh layer 172 to the printed circuit board layer 1172. A matching layer 205 can be located rearward of the supplemental FSS structure 1000, closer to the plane of the first FSS 170. Another matching layer 204 can extend forward of the first FSS 170 and the supplemental FSS structure 1000. The matching layers can be configured to reduce reflection of RF energy emitted by the array of radiating elements located rearward of the respective matching layer. Further discussion of exemplary matching layers and FSSs can be found in U.S. Patent Application Serial No. 17 / 787,619, the contents of which are incorporated by reference as if recited in full herein.

[0098] The base station antenna 100’ can have a pair of laterally spaced apart and longitudinally extending rails 128. The supplemental FSS structure 1000 can extend laterally between and be attached to the rails 128.

[0099] The supplemental FSS structure 1000 can be parallel to the first FSS 170 and / or the main reflector 214.

[0100] Referring to Figure 9 , at least a portion of the supplemental FSS structure 1000 can be located in a common plane as the first FSS 170. However, the supplemental FSS structure 1000 can be located in any plane and can be in a different plane than the first FSS 170, including forward or rearward of the plane of the first FSS 170. As shown in Figure 5A , for example, at least a portion of the supplemental FSS structure 1000 can be located in a plane forward of the plane of the first FSS 170.

[0101] Referring to Figure 5AIn some cases, the base station antenna 100' can include a first linear array 220-1 of first radiating elements 222 and a second linear array 220-2 of first radiating elements 222. A single one of the first radiating elements 222 of the first linear array 220-1 and a single one of the first radiating elements 222 of the second linear array 220-2 can be positioned in front of the supplemental FSS structure 1000. In some cases, the single one of the first radiating elements 222 of the second linear array 220-2 can protrude in front of the supplemental FSS structure 1000.

[0102] Still referring to Figure 5A , the base station antenna 100' can further include a plurality of columns 230-1, 230-2, 230-3, 230-4 of laterally spaced apart second radiating elements 232. In Figure 5A some exemplary embodiments, only two rows in each of the plurality of columns 230-1, 230-2, 230-3, 230-4 of second radiating elements 232 protrude in front of the supplemental FSS structure 1000.

[0103] Referring to Figure 7 , the base station antenna 100' can include a cradle 1214 that laterally extends between a pair of longitudinally extending rails 128. The cradle 1214 can be attached to a bottom portion of the supplemental FSS structure 1000 and to the main reflector 214.

[0104] The cradle 1214 can have a U-shape, with an arm 1214a of the U-shape facing down over the main reflector 214. A closed end 1214c of the U-shape is attached to the supplemental FSS structure 1000. The first FSS 170 can be attached to a top portion of the supplemental FSS structure 1000, spaced apart from the cradle 1214.

[0105] The metal mesh layer 172 includes an array 172a of unit cells 172u in a first pattern that extends behind the first linear array 220-1 and the second linear array 220-1 of first radiating elements 222, behind the plurality of columns 230-1, 230-2, 230-3, 230-4 of second radiating elements 232 and in front of the plurality of column arrays of third radiating elements 1195 across at least a substantial portion of a lateral dimension of the base station antenna 100 Figure 8 , 9 ).

[0106] In some embodiments, the supplemental FSS structure 1000 can be at a common electrical ground with the first FSS 170 and the main reflector 214.

[0107] The supplemental FSS structure 1000 can be configured to reflect and / or block RF energy in the first and second frequency bands. The second frequency band includes frequencies that are higher than the first frequency band, and allows energy from the mMIMO radiating elements 1195 positioned behind the supplemental FSS structure 1000 in a third frequency band that includes frequencies higher than the second frequency band to propagate therethrough. In some embodiments, one of the mesh layer 172 and the printed circuit board layer 1172 can be configured to substantially reflect RF energy in the operating frequency band of the first radiating elements 220 and / or the second (mid-band) radiating elements 232, while substantially passing RF energy in the operating frequency band of the mMIMO radiating elements 1195, while the other of the mesh layer 172 and the printed circuit board layer 1172 can be configured to substantially reflect RF energy in the operating frequency band of the second radiating elements 232 and / or the first radiating elements 222, while substantially passing RF energy in the operating frequency band of the mMIMO radiating elements 1195.

[0108] The base station antenna 100’ can include the active antenna elements / modules 110 positioned behind a rear 100r of a housing 100h that encloses the first FSS 170, the supplemental FSS structure 1000, and the main reflector 214. Figure 9

[0109] The supplemental FSS structure 1000 and the first FSS 170 can be configured to allow RF energy in at least a portion of the 3.2-4.1 GHz frequency band to propagate therethrough.

[0110] The base station antenna 100’ can include a plurality of feed plates 1200 coupled to the supplemental FSS structure 1000. At least some of the plurality of feed plates 1200 can have a lattice body 1200b with an aperture 1205 surrounded by linear segments 1204 that define at least a first conductive signal trace and a second conductive signal trace 1325, and the first and second conductive signal traces can extend downwardly over the main reflector 214. Figure 5A 18 Figure 5A

[0111] At least some of the linear segments 1204 of the feed plates 1200 are aligned with the metal segments of the unit cells 172u that form the metal mesh layer 172.

[0112] Referring to Figure 5A , at least some of the linear segments 1204 / 1325 of the feed plates 1200 extend downwardly over the main reflector 214.

[0113] In some embodiments, as Figure 5B ,​​​​7 As shown in FIG. 1, the first FSS 170 terminates above the supplemental FSS structure 1000.

[0114] In some embodiments, the metal mesh layer 172 can be configured to block RF energy from the mid-band radiating elements 232, and the printed circuit board layer 1172 can be configured to block RF energy from the low-band radiating elements 222.

[0115] In other embodiments, the metal mesh layer 172 can be configured to block RF energy from the low-band radiating elements 222, and the printed circuit board layer 1172 can be configured to block RF energy from the mid-band radiating elements 222.

[0116] In some embodiments, the metal mesh layer 172 can be configured to block RF energy from the low-band radiating elements 222 and the mid-band radiating elements 232, and the printed circuit board layer 1172 can be configured to block RF energy from the low-band radiating elements 222 and the mid-band radiating elements 232.

[0117] When a longer array of third-band radiating elements 1195 is used in the active antenna unit 110, the supplemental FSS structure 1000 can be used with the first FSS 170 and the main reflector 214, and for its shorter version, the supplemental FSS structure 1000 can be omitted, thus reducing manufacturing / assembly costs.

[0118] Figure 8 is a simplified illustration of the base station antenna 100’ showing the supplemental FSS structure 1000 with stacked metal mesh layer 172 and printed circuit board layer 1172 each having an array of unit cells 172a, 1172a, respectively. The unit cells 172u of the FSS 170 and / or the unit cells 1172u of the printed circuit board layer 1172 and / or the pattern of the metal mesh layer 172 can vary in length and / or laterally, or can be the same. For example, different arrangements of unit cells 172u, 1172u can be positioned relative to the first radiating elements 222 adjacent to the second radiating elements 232. The stacked layers 172, 1172 can be abutting or spaced apart in the fore-aft direction.

[0119] Figure 5B is shown with the stacked layers 172, 1172 closely spaced apart by a distance in the fore-aft direction, which can be in the range of 0.1 mm to 35.4 mm, for example, about 21 mm.

[0120] Figure 5CThe supplemental FSS structure 1000' is shown that can be configured to provide only the metallic mesh layer 172 and position the metallic mesh layer 172 in front of a portion of the first FSS 170, whereby the first FSS 170 extends behind and across / along a portion of the supplemental FSS structure 1000'. A subset of the radiating elements 222 in the first array 220-1 and the second array 220-2 protrude in front of the first FSS 170, and another smaller subset (e.g., 1-4) protrude in front of the supplemental FSS structure 1000', while a third subset protrude in front of the main reflector 214.

[0121] As shown in Figure 5C The first subset of the first-band radiating elements 222 overlap the reflector 214 in the forward direction perpendicular to the plane defined by the main surface of the reflector 214, and the second subset of the first-band radiating elements 222 overlap the first FSS 170 in the forward direction. The supplemental frequency selective surface (FSS) structure 1000' overlaps at least one of the first FSS 170 and the second subset of the first-band radiating elements 222 in the forward direction, but does not overlap all of the second subset of the first-band radiating elements 222 in the forward direction.

[0122] Both the supplemental FSS structure 1000, 1000' and the first FSS 170 can be provided in multiple layers of the same or different pattern units.

[0123] The first FSS 170 can be located behind and vertically above the FSS structure 1000.

[0124] As shown in Figure 9 The supplemental FSS structure 1000 can be aligned with one or both of the main reflector 214 and the first FSS 170, generally in the front-to-back direction of the base station antenna 100', to at least partially lie in a vertically extending plane common to one or both of the first FSS 170 and the main reflector 214.

[0125] Figure 10 An exemplary configuration of an array of radiating elements 1195 of an active antenna element 110 is shown.

[0126] Figure 11 The supplemental FSS structure 1000 is shown with unit cells 172u, 1172u of different configurations, sandwiched between a front matching layer 203 and a back matching layer 205, and between a front radome surface 111f and a back radome surface 111r, respectively.

[0127] The unit cells 170a, 1172a of the two components can have unit cells of the same or different configurations on at least some portions thereof.

[0128] Figure 5A 、 5B The supplemental FSS structure 1000 of 5C, 7 can provide performance of gain, directivity, and / or CPR similar to the arrangement of Figure 4 while allowing the second radiating element 222 to be mounted in front of the mMIMO radiating element 1195.

[0129] In some embodiments, the supplemental FSS structure 1000 can be electrically and mechanically coupled to the main reflector 214 and the first FSS 170.

[0130] The first FSS 170 and the printed circuit board layer 1172 of the supplemental FSS structure 1000 can be provided as non-metallic substrates with electrically conductive metal patches arranged to define unit cell 170u, 1172u arrays, respectively. The term “unit cell” can also be referred to interchangeably as “pattern unit.” Although the printed circuit board layer 1172 is described as a “layer,” the term “layer” is used broadly and can refer to a component that is multi-layered, e.g., the printed circuit board layer 1172 is typically a multi-layered printed circuit board, which can be constructed as a rigid, semi-rigid member or a flexible circuit.

[0131] In some embodiments, the first FSS 170 and / or the supplemental FSS structure 1000 can include one or more non-metallic substrates that can be or can include plastic, polymer, co-polymer, and / or dielectric with a metallized surface that provides electrically conductive patches that define at least a portion of the unit cell array.

[0132] The metal mesh layer 172 can be provided as a metal (e.g., aluminum) sheet, where the metal sheet is shaped to form the unit cell 172u array 172a. The unit cell 172u array can be stamped, etched, or laser shaped apertures that are formed through the metal sheet or can be formed in other ways.

[0133] The term "FSS" refers to a frequency selective surface and / or substrate (interchangeably referred to as "frequency selective surface" and "frequency selective reflector") that is structured to allow RF energy (electromagnetic waves) to pass in one or more first frequency bands and structured to reflect RF energy at one or more different second frequency bands. Thus, a frequency selective surface and / or substrate can also be interchangeably referred to herein as an "FSS." An FSS can selectively reject certain frequency bands and pass others through it to operate in the type of a "spatial filter" by including a frequency selective surface and / or substrate. See, e.g., Ben A. Munk, Frequency Selective Surfaces: Theory and Design, ISBN: 978-0-471-37047-5; DOI: 10.1002 / 0471723770; April 2000, Copyright © 2000 John Wiley & Sons, Inc., the contents of which are hereby incorporated by reference as if recited in full herein. 2000 John Wiley & Sons, Inc., the contents of which are hereby incorporated by reference as if recited in full herein.

[0134] The frequency selective surface and / or substrate material can include one or more of metamaterials, suitable RF materials, or even air (although air can require more complex components). The term "metamaterial" refers to a composite electromagnetic (EM) material. Metamaterials can include sub-wavelength periodic microstructures.

[0135] The FSS material of the first FSS 170 and / or the printed circuit board layer 1172 can be provided as one or more cooperating layers. The FSS material can include a substrate having a dielectric constant in the range of about 2-4 (e.g., about 3.7) and a thickness of about 5 mils, and a metal pattern forming unit cells 170u, 1172u formed on the dielectric substrate. The thickness can vary, but thinner materials can provide lower loss.

[0136] In some embodiments, the metal mesh layer 172 and the first FSS 170 can be structured to act as a high pass filter that substantially allows low band energy (e.g., energy in the 600-1000 MHz frequency range) to be substantially reflected (the FSS can act as a metal sheet), while allowing higher band energy (e.g., about 3.5 GHz or higher) to be substantially passed.

[0137] The first FSS 170 and the supplemental FSS structure 1000, 1000' are substantially transparent or invisible to higher band energy and provide a suitable out-of-band rejection response. The FSS material can allow for reduced filters, or even eliminate the filter requirements of the review radio 1120( Figure 8 9 ).

[0138] ​The first FSS 170 and the supplemental FSS structure 1000, 1000' can be disposed at locations corresponding to mounting locations of the active antenna modules 110 of the base station antenna 100', and can be configured to allow electromagnetic waves in a predetermined frequency range (e.g., high frequency electromagnetic waves in a range of 2300 to 4200 MHz or a portion thereof) to pass therethrough. In this way, when the base station antenna 100' is assembled, high frequency electromagnetic waves emitted by the active antenna modules 110 can pass through the first FSS 170 and the supplemental FSS structure 1000, 1000'.

[0139] Referring to Figure 12A-12C In some embodiments, the metal mesh layer 172 includes feed board apertures 1210 and corresponding feed boards 1200 covering some or all of the corresponding feed board apertures 1210. Figure 12A A metal mesh layer 172 having exemplary feed board apertures 1210 and a perimeter 1210p of the feed board apertures 1210 is shown. Figure 12B An exemplary feed board 1200 having a feed stalk 1220 is shown. Figure 12C An assembly view of the metal mesh layer 172 shown in Figure 12A An assembly view of the metal mesh layer 172 shown in Figure 12B An assembly view of the feed board 1200 shown in

[0140] Referring to Figure 12C In some embodiments, the metal mesh layer 172 can include an array of unit cells or pattern cells 172u. The plurality of pattern cells 172u can surround the feed board apertures 1210. The perimeter 1210p of the feed board apertures 1210 can extend through one or more of the unit pattern 172u such that the unit cells 172u surrounding the perimeter 1210p are incomplete patterns relative to other unit cells 172u and thus have a different shape than the other unit cells 172u. The feed board perimeter 1210p can define a plurality of corner segments 172c of the set of unit cells surrounding the feed board perimeter 1210p. The corner segments 172c can be curvilinear and can have a portion extending at an angle β (see Figure 12A ) that is different from and / or has a different length than the corner segments 172c of the unit cells 172u spaced apart from the feed board apertures 1210. In some embodiments, the angle β can be between 30-60 degrees from the horizontal. The unit cells 172u (shown as four unit cells 172u in Figure 12A ) surrounding the respective feed board apertures 1210 can have a perimeter 172pf that has a different shape than the perimeters 172p of the other unit cells 172u.

[0141] The feed board 1200 can have a perimeter 1200p and / or a shaped portion 1200m Figure 12C , 14), the perimeter and / or shaped portions are configured to cooperate with the metal mesh layer 172 to replicate at least a portion of the unit cell 172u structure. The feed plate 1200 can have at least a portion that is shaped to correspond to the shape of a unit cell 172u (or a portion of the shape of a unit cell 172u). Figure 12B It is shown that the perimeter 1200p is curved and includes four corner segments 1200c having a shape that corresponds to a unit cell 172u. Figure 12C It is shown that the corner segments 1200c can be positioned over or under the corresponding unit cell 172u when assembled. The feed plate 1200 can be positioned in front of the metal mesh layer 172 or behind the metal mesh layer 172. The corner segments 1200c can be coupled to the front-facing surface or rear-facing surface of the corresponding unit cell of the unit cells 172u of the metal mesh layer 172. The corner segments 1200c on the front-facing or rear-facing major surface can include a conductive metal (e.g., copper) and define a portion of the ground plane 1230. As shown, the ground plane 1230 is discontinuous across the front or rear of the feed plate 1200 such that the pattern of unit cells 172u is replicated on the feed plate 1200.

[0142] The ground plane 1230 of the feed plate 1200 can cooperate with the metal mesh layer 170 to form a portion of the unit cell structure and / or the functionality of the FSS of the mesh layer 172.

[0143] The feed plate aperture 1210 can have a surface area Sf that is greater than the surface area Su of a unit cell 172u, typically greater than at least two unit cells 172u and less than 10 (ten) unit cells 172u, where the unit cells 172u can have the same surface area, or an average value with a maximum and minimum value, where they differ. However, it should be appreciated that in some embodiments, since the feed plate 1200 replicates the pattern of unit cells 172u and thus acts as an FSS surface, the feed plate aperture 1210 can have any size and can replace a greater number of unit cells 172u of the metal mesh layer 172.

[0144] In some embodiments, the feed stalks 1220 of each radiating element 222 can comprise printed circuit board-based feed stalks, but alternatively, die cast or sheet metal feed stalks can be used. When implemented using printed circuit boards, the feed stalks 1220 can comprise a pair of printed circuit boards having cooperating slots that allow the two printed circuit boards to be joined together with the printed circuit boards rotated 90 degrees relative to each other, as is well known in the art. In such embodiments, each printed circuit board typically includes two rearwardly extending tabs 1220 / that facilitate fixedly mounting the radiating element 222 to the feed plate 1200 by soldering. The feed stalks 1220 can have a plurality of rearwardly extending tabs 1220 / (four tabs are shown in the depicted embodiment) that extend rearwardly through the feed plate 1200. Two coaxial feed cables 1225 (one for each polarization) Figure 14 ) can be provided and they can be located rearward of the mesh layer 172. Each coaxial cable 1225 can be connected to one of the rearwardly extending tabs 1220 / of a respective one of the printed circuit boards of 1220 so as to transfer RF signals between the radiating elements 222 and the feed network of the passive antenna assembly 190.

[0145] Since the coaxial cables 1225 can be coupled directly to the feed stalks 1220 rearward of the feed plate 1200, there is no need for signal transfer traces on the front surface of the feed plate 1200, e.g., the front surface 1200 / of the feed plate 1200 can be free of metal. One major surface of the feed plate 1200 can include a conductive electrical ground plane 1230, which can be a copper layer. The ground plane 1230 can be on the rear major surface 1200r Figure 17A ) or on the front major surface 1200f Figure 17B . The ground plane 1230 can be structured to occupy only a sub-portion of the surface area of the major front or rear surface of the feed plate 1200 provided by the patterned segments thereon.

[0146] Referring to Figure 17A and 17B , for example, the center conductor 1225c of the coaxial cable 1225 can be connected to a signal trace 1223 on the front portion 1220 / of at least one tab 1220 / of the feed stalk 1220 and the ground conductor of the coaxial cable can be connected to a ground plane on the feed plate 1200.

[0147] Figure 13It is shown that the feed panel aperture 1210 can be polygonal, such as square or rectangular, and can be coupled to a single feed panel 1200 with a single feed stalk 1220 of a radiating element 222 or 232. The feed panel 1200, or at least a portion thereof, is a shaped segment 1200m in the form of all or a portion of a unit cell 172u, does not require, and typically does not have, signal transmission traces. The feed panel 1200 can have a perimeter 1200p (shown in dashed line in front of the back surface of the mesh layer 172) that has at least a portion that extends beyond the feed panel aperture 1210 to physically couple there to the mesh layer 172.

[0148] Figure 14 Another configuration of the feed panel aperture 1210 and feed panel 1200 is shown. The ground plane 1230 of the feed panel 1200 can have a unit cell shaped segment 1230u that is shaped to mimic or be identical to the unit cell 172u of the mesh layer 172. The ground plane 1230 can also include a ground strip 1231 that aligns with the metal strip 172s of the unit cell 172u (and panel) array that can be coupled with the metal capacitance of the mesh layer 172, such as with one or more unit cells 172u, to provide a capacitive connection between the mesh layer 172 and the feed panel 1200.

[0149] Figure 15 and 16 A feed panel aperture 1210 and feed panel 1200 similar to that shown in Figure 12A-12C A feed panel aperture 1210 and feed panel 1200 similar to that shown in

[0150] For example, Figure 14-16Embodiments are shown in which a combination of unit cells 172u of the mesh layer 172 and the feed plate 1200 are used to replicate and / or form at least a portion of the structure of the unit cells 172u of the mesh layer 172 on the feed plate 1200 to provide a continuous unit cell structure. The metal pattern on the feed plate 1200 can be capacitively coupled to the mesh layer 172 through overlapping sections having the same shape and / or pattern. The result is that the feed plate 1200 and the mesh layer 172 together act as a mesh reflector that provides FSS. This allows mid-band and / or low-band radiating elements to be positioned in front of and above or on the mesh layer 173 and to be fed without any substantial impairment to the performance of these radiating elements. The metal pattern on the feed plate 1200 can have the same shape as the metal pattern of the mesh layer 172, and the metal on the feed plate 1200 can be coupled to the metal of the metal mesh layer 172.

[0151] In other embodiments, the metal mesh layer 173 need not be electrically coupled to the metal on the feed plate 1200.

[0152] The metal on the feed plate 1200 can be combined with the cutouts / apertures 1210 to contribute the same pattern or pattern features of all or a portion of one or more unit cells 172u of the mesh layer 172.

[0153] Figure 17A Embodiments are shown in which the ground layer 1230 can be disposed on the back surface 1200r of the feed plate 1200 and no signal transmission traces for the radiating elements are needed on the front surface 1200f. As shown, the center conductor 1225c of the coaxial feed cable 1225 can be directly soldered to the feed stalk 1220. The ground conductor 1225c of the coaxial feed cable 1225 can be directly soldered to the ground layer 1230 on the back surface 1200r of the feed plate 1200.

[0154] Figure 17B Embodiments are shown in which the ground layer 1230 can be disposed on the front surface 1200f of the feed plate 1200 and no signal traces for the radiating elements are needed on the front surface 1200f. As shown, the coaxial feed cable 1225 can extend through a hole in the feed plate 1200 to its front side. The center conductor 1225c of the coaxial feed cable 1225 can be directly soldered to the feed stalk 1220 and the ground conductor of the coaxial feed cable 1225 can be directly soldered to the ground layer 1230 on the front surface 1200r of the feed plate 1200.

[0155] Figure 17A and 17BAlso shown are fastening segments 1212 on the outer periphery of the feed plate 1200, which are configured to be coupled to the unit cells 172u of the mesh layer 172. The fastening segments 1212 can be provided in any suitable number, which can generally be in the range of 2-4. The fastening segments 1212 provide a structure for fastening the feed plate 1200 to the mesh layer 172 (e.g., by welding, by fasteners, by adhesive tape, etc.), and can also form a capacitive connection between the ground layer or plane 1230 on the feed plate 1200 and the mesh layer 172, such that both structures are at a common ground potential. In Figure 17A In the embodiment of FIG. 12, the center conductor is on the bottom side of the feed plate 1200 (printed circuit board). Figure 17A One difference between the embodiments of FIGS. 11 and 12 is the location of the solder joint between the center conductor and the dipole handle. Figure 17B In the embodiment of FIG. 11, the solder joint is on the bottom, and Figure 17A In the embodiment of FIG. 12, the solder joint is on the top side. Figure 17B

[0156] While the above discussion assumes a capacitive connection between the feed plate 1200 and the metal mesh layer 172, embodiments of the present application are not limited thereto. In other embodiments, the feed plate 1200 can be galvanically coupled to the mesh layer 172 (e.g., by welding).

[0157] Radiating elements in front of the metal mesh layer 172 can include low band 222 and / or mid band 232 radiating elements (FIG. 5).

[0158] The feed plate 1200 can cooperate with the mesh layer 172 to reflect energy of the low band and / or mid band radiating elements, while being transparent or “invisible” to high band radiating elements such as mMIMO elements 1195 (FIG. 5) positioned behind the first FSS layer 170 and the supplemental FSS 1000 having the mesh layer 172. Figure 8 9

[0159] The pattern units or unit cells 172u can be periodically arranged in the lateral and longitudinal directions of the base station antenna 100. Each of the pattern units / unit cells 172u can have a predetermined pattern, and can include a capacitor structure and an inductor structure connected in series and / or in parallel with the capacitor structure. In addition, each of the pattern units 172u can be electrically connected to each other through the inductor structure. For example, the inductor structure in each pattern unit / unit cell 172u can be electrically connected to the inductor structure of an adjacent pattern unit.

[0160] ​​​The resonant frequencies of the frequency selective surfaces of the mesh layer 172 and the printed circuit board layer 1172 can be constructed by selecting or designing the pattern and size of the capacitor structure and the inductor structure of each pattern unit / cell unit 172u, 1172u, and the spacing and arrangement of the plurality of pattern units 172u, 1172u, such that electromagnetic waves in a predetermined frequency range can pass through the frequency selective sections.

[0161] Further, the cell / pattern units 172u can have various shapes, such as triangle, rectangle, diamond, pentagon, hexagon, circle, ellipse, partial ellipse, etc., and combinations of different shapes for different cell units. Further details of exemplary FSS meshes can be found in co-pending PCT / CN2022 / 080578, the contents of which are incorporated by reference as if recited in full herein.

[0162] In some embodiments according to the present disclosure, the first FSS 170 and the printed circuit board layer 1172 can include patch-type frequency selective sections, which can be implemented by forming periodically arranged metal pattern units on a substrate. The plurality of metal pattern units can be formed on the substrate by a selective plating process or a metal ink transfer printing process. In some embodiments, the substrate can be formed of plastic, and the metal pattern units can be formed of metal materials such as copper, aluminum, gold, and silver. To increase the strength of the frequency selective surface, the substrate can be formed of high-strength plastic.

[0163] In some embodiments, the mesh layer 172 and / or the printed circuit board layer 1172 can be located at a distance in the range of 1 / 8 wavelength to 1 / 4 wavelength of the operating wavelength behind the low-band (dipole) radiating elements 222. The term “operating wavelength” refers to the wavelength corresponding to the center frequency of the operating frequency band of the radiating elements (e.g., the low-band radiating elements 222). In some embodiments, the mesh layer 172 and / or the printed circuit board layer 1172 can be located at a distance in the range of 1 / 10 wavelength to 1 / 2 wavelength of the operating wavelength in front of the high-band radiating elements 1195( Figure 8 、 Figure 9 ) of the active antenna module 110( Figure 8 、 Figure 9 ) can be located at a physical distance of 0.25 inches and 2 inches from the ground plane or reflector 1174 behind the mMIMO array of radiating elements 1195 of the active antenna module 110(

[0164] In some embodiments, the ground plane or reflector 1174 of the active antenna module 110( Figure 8The supplemental FSS structure 1000 and / or the first FSS 170 and / or the main reflector 214 can be electrically coupled to the base station antenna 100', e.g., galvanically coupled and / or capacitively coupled. In other embodiments, the ground plane or reflector 1174 of the active antenna module 110 is not electrically coupled to the supplemental FSS structure 1000, the first FSS 170, and the main reflector 214.

[0165] Referring to Figure 5A The passive antenna assembly 190 includes a plurality of arrays of radiating elements, typically arranged as four to eight columns, with the radiating elements extending forward from the front side of the main reflector 214, with some columns of radiating elements continuing to extend forward of the first FSS 170 and the grid layer 172. The various arrays of radiating elements of the antenna assembly 190 can include radiating elements 222 configured to operate in a first frequency band and radiating elements 232 configured to operate in a second frequency band. Other arrays of radiating elements can include radiating elements configured to operate in the second frequency band or a third frequency band. The first, second, and third frequency bands can be different frequency bands (although can overlap). In some embodiments, some low-band antenna elements 222 with dipole arms can be located forward of the first FSS layer 170, other low-band antenna elements can be located forward of the main reflector 214, and still other low-band antenna elements can be located forward of the supplemental FSS structure 1000, 1000'.

[0166] The passive antenna assembly 190 of the base station antenna 100 can include one or more arrays of low-band radiating elements 222, one or more arrays of mid-band radiating elements 232. The radiating elements 222, 232, 1195 can each be dual-polarized radiating elements. Further details of the radiating elements can be found in co-pending WO2019 / 236203 and WO2020 / 072880, the contents of which are incorporated by reference as if recited in full herein. Some of the high-band radiating elements, such as the radiating elements 1195, can be provided as mMIMO antenna arrays and can be disposed in the active antenna module 110 rather than in the housing 100h of the base station antenna 100.

[0167] The low-band radiating elements 222 can be mounted to extend forward from the main or primary reflector 214, the first FSS 170, and the supplemental FSS structure 1000, 1000', and can be mounted in two columns to form two linear arrays 220-1, 220-2 of low-band radiating elements 222. In some embodiments, each low-band linear array 220-1, 220-2 can extend along substantially the full length of the antenna 100.

[0168] The low-band radiating elements 222 can be configured to transmit and receive signals in a first frequency band. In some embodiments, the first frequency band can include a 617-960 MHz frequency range or a portion thereof (e.g., a 617-896 MHz band, a 696-960 MHz band, etc.). The low-band linear arrays can or can not be used to transmit and receive signals in the same portion of the first frequency band. For example, in one embodiment, the low-band radiating elements 222 in the first linear array can be used to transmit and receive signals in the 700 MHz band, and the low-band radiating elements 222 in the second linear array can be used to transmit and receive signals in the 800 MHz band. In other embodiments, the low-band radiating elements 222 in both the first linear array and the second linear array can be used to transmit and receive signals in the 700 MHz (or 800 MHz) band.

[0169] Some of the mid-band radiating elements 232 can likewise be mounted to extend forward from the supplemental FSS structure 1000, 1000', some to extend forward from the main reflector 214, and can be mounted in columns to form a linear array of first mid-band radiating elements. The mid-band radiating elements 232 can be configured to transmit and receive signals in a second frequency band. In some embodiments, the second frequency band can include a 1427-2690 MHz frequency range or a portion thereof (e.g., a 1710-2200 MHz band, a 2300-2690 MHz band, etc.). In the depicted embodiment, the mid-band radiating elements 232 are configured to transmit and receive signals in a lower portion of the second frequency band (e.g., some or all of the 1427-2200 MHz band). The linear array of mid-band radiating elements 232 can be structured to transmit and receive signals in the same portion of the second frequency band or in a different portion of the second frequency band.

[0170] Other mid-band radiating elements can be mounted in columns to form a linear array of second mid-band radiating elements and can be configured to transmit and receive signals in the second frequency band. For example, the mid-band radiating elements can transmit and receive signals in an upper portion of the second frequency band (e.g., some or all of the 2300-2700 MHz band). There can be first and second mid-band radiating elements, and they can have different designs from one another.

[0171] The high-band radiating elements 1195 can be configured to transmit and receive signals in a third frequency band. In some embodiments, the third frequency band can include a 3300-4200 MHz frequency range or a portion thereof.

[0172] It will also be appreciated that the number of linear arrays of low-band, mid-band, and high-band radiating elements can be different than that shown in the figures. For example, the number of linear arrays of each type of radiating element can be different than shown, some types of linear arrays can be omitted and / or other types of arrays can be added, the number of radiating elements of each array can be different than shown, and / or the arrays can be arranged differently. As one specific example, two linear arrays of second mid-band radiating elements can be substituted for four linear arrays of ultra-high band radiating elements that transmit and receive signals in the 5 GHz band.

[0173] Each array of low-band radiating elements 222 can be used to form a pair of antenna beams, one for each of two polarizations at which the dual-polarized radiating element design is intended to transmit and receive RF signals. Likewise, each array of mid-band radiating elements 232 can be configured to form a pair of antenna beams, one for each of two polarizations at which the dual-polarized radiating element design is intended to transmit and receive RF signals. Each linear array can be configured to provide service to a sector of a base station. For example, each linear array can be configured to provide approximately 120° of coverage in an azimuth plane, such that the base station antenna 100' can be used as a sector antenna for a three-sector base station. Of course, it will be appreciated that the linear arrays can be configured to provide coverage over different azimuth beamwidths. While all of the radiating elements 222, 232, 1195 can be dual-polarized radiating elements in the depicted embodiment, it will be appreciated that in other embodiments, some or all of the dual-polarized radiating elements can be replaced with single-polarized radiating elements. It will also be appreciated that while the radiating elements are shown as dipole radiating elements in the depicted embodiment, other types of radiating elements can be used in other embodiments, such as, for example, patch radiating elements.

[0174] Since the radiating elements 222, 232 can be tilted cross-dipole radiating elements, the first polarization and the second polarization can be -45° polarizations and +45° polarizations.

[0175] Phase shifters ( Figure 7 ) can be connected to respective ones of the RF ports 140 ( Figure 3 , Figure 7 ). The phase shifters can be implemented as, for example, brush arc phase shifters, such as the phase shifters disclosed in U.S. Patent No. 7,907,096 to Timofeev, the disclosure of which is hereby incorporated in its entirety. A mechanical linkage can be coupled to a RET actuator (not shown). The RET actuator can apply a force to the mechanical linkage, which in turn adjusts a movable element on the phase shifter in order to electronically adjust a downtilt angle of an antenna beam generated by one or more of the low-band or mid-band linear arrays.

[0176] It should be noted that multiple-connector RF ports (also referred to as “cluster” connectors) can be used instead of individual RF ports 140. Suitable cluster connectors are disclosed in U.S. Patent Application Serial No. 16 / 375,530, filed April 4, 2019, the entire contents of which are incorporated herein by reference.

[0177] Radiating element 222 can be a cross-dipole element configured to operate in some or all of the 617-960 MHz band. Signal traces 1223 on feed stalks 1220 can be feed circuits including hook baluns. Further discussion of exemplary antenna elements including antenna elements, including feed stalks, can be found in U.S. Provisional Patent Application Serial Nos. 63 / 087,451 and 62 / 993,925 and / or related Utility Patent Applications claiming priority thereto, the contents of which are incorporated herein by reference as if recited in full herein. Figure 17A 17B Further discussion of exemplary antenna elements including antenna elements, including feed stalks, can be found in U.S. Provisional Patent Application Serial Nos. 63 / 087,451 and 62 / 993,925 and / or related Utility Patent Applications claiming priority thereto, the contents of which are incorporated herein by reference as if recited in full herein.

[0178] Turning now to Figure 18 19 An exemplary feed plate 1200 having a grid layer 172 is shown. In this embodiment, feed plate 1200 has a plurality of spaced-apart linear segments 1204 around one or more cutouts or apertures 1205, forming an open-lattice type body 1200b. Linear segments 1204 can include at least one signal trace 1200t, shown as a plurality of signal traces 1200t, which can define a respective at least one, preferably a plurality of, conductor signal paths 1325, shown as a first conductor signal path 13251 and a second, electrically isolated, conductor signal path 13252, each having a respective power divider or splitter 1326 that transfers a corresponding signal from a center conductor 1225c of a coaxial cable 1225 to at least a respective first and second shaped segment 1200m aligned with a respective feed stalk 1220. Shaped segments 1200m can have at least a portion of a curvilinear shape of a corresponding unit cell 172u of grid layer 172. Feed plate 1200 can define two or more conductive signal traces 1200t for two or more signal paths 1325, or a single signal trace for a single conductive signal path 1325. Signal traces 1200t can be provided as microstrip signal traces.

[0179] ​​The signal traces 1200t and the mesh layer 172 can together form a series of microstrip transmission lines for transmitting RF signals between one or more arrays of radiating elements of the base station antenna 100’ and other components of the base station antenna 100’ (e.g., phase shifters). In particular, the signal traces 1200t can act as signal traces of the microstrip transmission lines, and the metal mesh layer 172 can act as a ground plane of the microstrip transmission lines. The signal traces 1200t can be separated from the mesh layer by a dielectric layer (e.g., an air gap, a solder mask, or a dielectric substrate of a printed circuit board). In some embodiments, the mesh layer 172 can be formed as a metal layer on a first side of a dielectric substrate (e.g., a dielectric substrate of a printed circuit board), and the signal traces 1200t can be formed as a metal pattern on a second side of the dielectric substrate.

[0180] In embodiments where the metal mesh layer 172 and the feed boards 1200 are separate elements, each of the feed boards 1200 can include a fastening segment 1212 for attaching the feed board 1200’ to the mesh layer 172.

[0181] Each of the feed boards 1200 can have a first cable connector and a second cable connector 1207 attached to respective coaxial cables 1225 Figure 14 ) and connected to signal traces 1200t corresponding to respective first and second conductor signal paths 13251 and 13252. In particular, the center conductor Figure 14 ) of the coaxial cable 1225 is connected to signal traces 1200t corresponding to respective first and second conductor signal paths 13251 and 13252. The ground conductor Figure 14 ) of the coaxial cable 1225 can be connected to the mesh layer 172.

[0182] The signal traces 1200t can be arranged as a series of lateral and longitudinal linear segments 1204 that are aligned with the metallic linear features of the grid layer 172. This arrangement serves to convert the signal traces 1200t into microstrip transmission lines (as it positions a ground conductor behind each signal trace 1200t) and also positions the signal traces 1200t so that they do not block the openings in the structure of the unit cells 172u, which can degrade the performance of the frequency selective surface. The apertures 1205 of the lattice body 1200b can be sized and configured to provide open windows in front of or behind the plurality of unit cells 172u of the grid layer 172. A first subset of the linear segments 1204 can provide a first conductor signal path 13251 and a second subset of the linear segments 1204 can provide a second conductor signal path 13252. As noted above, in some embodiments, the lattice body 1200b can be selectively metalized on a non-conductive substrate (e.g., a printed circuit board implementation), but it will be appreciated that the lattice body 1200b can alternatively be formed of a sheet of metal or otherwise. It will also be appreciated that some or all of the linear segments 1204 can be replaced with non-linear segments (e.g., curved segments or serpentine segments). This can be particularly true where the unit cells 172u of the grid layer 172 have non-linear segments, as performance can be improved where the lattice body 1200b matches the underlying grid structure.

[0183] In some embodiments, the apertures 1205 can be cutouts in the dielectric of the printed circuit board that provide the signal traces 1200t and the corresponding conductor signal paths 13251, 13252. In other embodiments, the apertures 1205 can be non-metallized regions in the dielectric of the printed circuit board that provide the signal traces 1200t and the corresponding conductor signal paths 13251, 13252.

[0184] The feed plate 1200 can be used for any radiating element operating in any frequency band, such as the low-band radiating elements 222 and / or the mid-band radiating elements 232.

[0185] Additional discussion of example grid structures, feed plates, and feed stalks can be found in U.S. Patent Application Serial No. 18 / 326,239 or US2023 / 0395987, the contents of which are incorporated by reference as if recited in full herein.

[0186] Embodiments of the application have been described above with reference to the drawing, in which embodiments of the application are shown. The application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments were provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art. Throughout the specification, like drawing reference numerals denote like elements.

[0187] It will be understood that, although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0188] It will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.).

[0189] Relative terms, such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical", can be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0190] The term "about" used in connection with a number refers to + / - 10% variation.

[0191] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", when used herein, specify the presence of stated features, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and / or groups thereof.

[0192] Aspects and elements of all the embodiments disclosed above can be combined and / or combined with aspects or elements of other embodiments in any manner possible to provide additional embodiments.

Claims

1. A base station antenna comprising: a first frequency selective surface (FSS); a main reflector; and a supplemental frequency selective surface (FSS) structure located between the first FSS and the main reflector in a longitudinal direction. a metal mesh layer comprising an array of unit cells; 2. The base station antenna of Claim 1, wherein the supplemental FSS structure comprises: and a printed circuit board layer comprising an array of unit cells, wherein the metal mesh layer and the printed circuit board layer are aligned to be located in a substantially common footprint in the longitudinal direction and stacked in an anterior-posterior direction of the base station antenna.

3. The base station antenna of claim 2, wherein the metal mesh layer is located anterior to the printed circuit board layer.

4. The base station antenna of claim 1, further comprising a pair of laterally spaced apart and longitudinally extending rails, wherein the supplemental FSS structure laterally extends between and is attached to the rails.

5. The base station antenna of claim 1, wherein the supplemental FSS structure has a length, the main reflector has a length, and the first FSS has a length, all of which are in a longitudinal direction of the base station antenna, wherein the length of at least one layer of the supplemental FSS is in a range of 10-30% of the length of the first FSS and / or the main reflector.

6. The base station antenna of claim 5, wherein the supplemental FSS structure is parallel to the first FSS and the main reflector.

7. The base station antenna of claim 1, wherein at least a portion of the supplemental FSS structure is located anterior to a plane of the first FSS.

8. The base station antenna of claim 1, wherein the supplemental FSS structure comprises a metal mesh layer having an array of unit cells located in a plane anterior to a plane of the first FSS and having a longitudinal extent located only along a portion of the first FSS or configured to not overlap the first FSS.

9. The base station antenna of claim 8, wherein the base station antenna further comprises a feed plate coupled to the metal mesh layer, and wherein the feed plate is configured to replicate at least a portion of a unit cell shape of unit cells of the array of unit cells.

10. The base station antenna of claim 1, wherein the supplemental FSS structure comprises a metal mesh layer comprising at least one feed plate aperture and an array of unit cells, and wherein a feed plate extends across a portion of a plurality of unit cells of the array of unit cells surrounding the feed plate aperture and overlaps a portion of the plurality of unit cells.

11. The base station antenna of claim 10, wherein the feed plate comprises a metal shape replicating at least a portion of a shape of a unit cell structure of one or more unit cells of the plurality of unit cells, and wherein the metal shape overlaps at least some of the plurality of unit cells. ​ 12. The base station antenna of Claim 1, further comprising a first linear array of first radiating elements and a second linear array of first radiating elements, wherein a single one of the first linear array of first radiating elements and a single one of the second linear array of first radiating elements protrude forward from the supplemental FSS structure.

13. The base station antenna of Claim 11, further comprising laterally spaced apart multiple columns of second radiating elements, wherein only two rows in each of the multiple columns of second radiating elements protrude forward from the supplemental FSS structure.

14. The base station antenna of Claim 1, further comprising a bracket laterally extending between a pair of longitudinally extending rails, wherein the bracket is attached to a bottom portion of the supplemental FSS structure and the main reflector, wherein the bracket has a U-shape, wherein arms of the U-shape face downward on the main reflector.

15. The base station antenna of Claim 14, wherein a closed lateral extending end of the U-shape is attached to the supplemental FSS structure, and wherein the first FSS is attached to a top portion of the supplemental FSS structure.

16. The base station antenna of Claim 2, wherein the metal mesh layer comprises sidewalls that are angled outward from a main planar body thereof in a forward direction, and wherein the printed circuit board layer terminates laterally inward from the sidewalls of the metal mesh layer.

17. The base station antenna of Claim 16, wherein the sidewalls comprise an array of unit cells arranged in a repeating pattern along a length of the supplemental FSS structure.

18. The base station antenna of Claim 2, wherein the array of unit cells of the metal mesh layer are arranged in a first pattern that extends behind the first and second linear arrays of first radiating elements, behind the multiple columns of second radiating elements and in front of the multiple array of columns of third radiating elements across a majority of a lateral dimension of the base station antenna.

19. The base station antenna of Claim 1, wherein the supplemental FSS structure reflects and / or blocks energy in a first operational frequency band of the first radiating elements of the base station antenna and a second operational frequency band of the second radiating elements of the base station antenna, wherein the second frequency band comprises frequencies higher than the first frequency band, and the supplemental FSS structure allows energy from the mMIMO array of radiating elements in a third operational frequency band to propagate therethrough, wherein the third operational frequency band comprises frequencies higher than the second frequency band, and wherein at least some of the mMIMO array of radiating elements are positioned behind the supplemental FSS structure.

20. The base station antenna of Claim 1, further comprising an active antenna unit positioned behind a rear portion of an enclosure that encloses the first FSS, the supplemental FSS structure and the main reflector.

21. The base station antenna of Claim 20, wherein the supplemental FSS structure is structured to allow RF energy in at least a portion of the 3.2-4.1 GHz frequency band to propagate therethrough.

22. The base station antenna of Claim 1, further comprising a plurality of feed panels coupled to the supplemental FSS structure, wherein at least some of the plurality of feed panels have a lattice body having an aperture surrounded by linear segments defining at least a first conductive signal trace and a second conductive signal trace, and wherein the first and second conductive signal traces extend downwardly over the main reflector.

23. The base station antenna of Claim 22, wherein at least some of the linear segments of the feed panels are aligned with the metal linear segments of the metal mesh layer.

24. The base station antenna of Claim 22, wherein at least some of the linear segments of the feed panels extend downwardly over the main reflector.

25. The base station antenna of Claim 1, wherein the first FSS terminates above the supplemental FSS structure.

26. The base station antenna of Claim 2, wherein the metal mesh layer is configured to block and / or reflect RF energy from mid-band radiating elements, and wherein the printed circuit board layer is configured to block and / or reflect RF energy from low-band radiating elements.

27. The base station antenna of Claim 2, wherein the metal mesh layer is configured to block and / or reflect RF energy from low-band radiating elements, and wherein the printed circuit board layer is configured to block and / or reflect RF energy from mid-band radiating elements.

28. The base station antenna of Claim 2, wherein the metal mesh layer is configured to block and / or reflect RF energy from low-band radiating elements and mid-band radiating elements, and wherein the printed circuit board layer is configured to block and / or reflect RF energy from low-band radiating elements and mid-band radiating elements.

29. A base station antenna, comprising: a reflector; a first frequency selective surface (FSS); an array of first frequency band radiating elements, all coupled to a first radio frequency (RF) input, wherein a first subset of the first frequency band radiating elements overlap the reflector in a forward direction perpendicular to a plane defined by a major surface of the reflector, and a second subset of the first frequency band radiating elements overlap the first FSS in the forward direction; and a supplemental frequency selective surface (FSS) structure that overlaps at least one of the first FSS and the second subset of the first frequency band radiating elements in the forward direction, but does not overlap all of the second subset of the first frequency band radiating elements in the forward direction.

30. The base station antenna of Claim 29, further comprising an array of second band radiating elements all coupled to a second RF input, wherein a first subset of the second band radiating elements overlap the reflector in the forward direction and a second subset of the second band radiating elements overlap both the first FSS and the supplemental FSS in the forward direction, wherein a second band encompasses higher frequencies than a first band.

31. The base station antenna of Claim 30, wherein the supplemental FSS is structured to reflect RF energy in an operational frequency band of the array of second band radiating elements.

32. The base station antenna of Claim 30, wherein none of the second band radiating elements overlap the first FSS.

33. The base station antenna of Claim 30, wherein only some of the array of second band radiating elements protrude forward from the supplemental FSS.

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