Passive / active antenna system with improved frequency selective surface

Abstract

A base station antenna includes an array of lower band radiating elements, an array of higher band radiating elements, and a frequency selective surface having a plurality of unit cells. The equivalent circuit of each unit cell includes a first shunt inductor-capacitor ("LC") circuit embedded within a second shunt LC circuit.

Description

Technical Field

[0001] The present disclosure relates to communication systems, and in particular to base station antennas for cellular communication systems. Background Art

[0002] Cellular communication systems are well known in the art. In a cellular communication system, a geographic area is divided into a series of areas called "cells" that are served by corresponding base stations. Each base station may include one or more base station antennas configured to provide two-way radio frequency ("RF") communications with mobile users within the cell served by the base station. Typically, the base station antenna is mounted on a tower or other elevated structure, with a radiation pattern (also referred to herein as an "antenna beam") generated by the base station antenna pointing outward.

[0003] A common base station configuration is a three-sector configuration, in which the cell is divided into three 120° sectors in the azimuth (horizontal) plane. A separate base station antenna provides coverage (service) for each sector. Typically, each base station antenna will include multiple vertically extending columns of radiating elements that operate, for example, using second-generation ("2G"), third-generation ("3G"), or fourth-generation ("4G") cellular network protocols. These vertically extending columns of radiating elements are often referred to as "linear arrays" and can be straight columns of radiating elements or columns in which some of the radiating elements are staggered horizontally to reduce the beamwidth of the antenna beam generated in the azimuth plane. Most modern base station antennas include "low-band" linear arrays of radiating elements that support services in some or all of the 617-960 MHz frequency bands, and "mid-band" linear arrays of radiating elements that support services in some or all of the 1427-2690 MHz frequency bands. These linear arrays are typically formed using dual-polarized radiating elements, which allows each array to transmit and receive RF signals with two orthogonal polarizations.

[0004] Each of the aforementioned linear arrays of dual-polarized radiating elements is coupled to two ports of the radio (one port for each polarization). The RF signal transmitted by the linear array is passed from the radio to the antenna, where it is split into a plurality of subcomponents, each of which is fed to a corresponding subset of the radiating elements in the linear array (typically, each subcomponent is fed to one to three radiating elements). The subcomponents of the RF signal are transmitted by the radiating elements to generate an antenna beam that covers a generally fixed coverage area (e.g., a sector of a cell). Typically, these linear arrays will have remote electronic tilt ("RET") capability, which allows the cellular operator to change the pointing angle of the generated antenna beam in the elevation (vertical) plane in order to change the size of the sector served by the linear array. Because the antenna beam generated by the aforementioned 2G / 3G / 4G linear arrays generates a static antenna beam whose shape changes only due to occasional adjustments to the downtilt angle of the antenna beam, the aforementioned linear arrays are often referred to as "passive" linear arrays.

[0005] Cellular operators are upgrading their networks to support fifth generation (“5G”) cellular service. An important component of 5G cellular service is the use of so-called multi-column “active” beamforming arrays that work in conjunction with beamforming radios to dynamically adjust the size, shape, and pointing direction of the antenna beams generated by the active beamforming arrays. These active beamforming arrays are typically formed using “high-band” radiating elements that operate in higher frequency bands, such as some or all of the 3.3-4.2 GHz band and / or the 5.1-5.8 GHz band (or in the 2.3-2.7 GHz portion of the mid-band frequency range). The radiating elements in each column of such an active beamforming array are typically coupled to corresponding ports of a beamforming radio. The beamforming radio may be a separate device or may be integrated with the active antenna array. A beamforming radio can adjust the amplitude and phase of a subcomponent of the RF signal fed to each port of the radio (and therefore to each corresponding column of radiating elements in a multi-column beamforming array) to generate antenna beams with narrowed beamwidths (and therefore higher antenna gain) in the azimuth and / or elevation planes. These narrowed antenna beams can be electronically steered by properly selecting the amplitude and phase of the subcomponents of the RF signal output by the beamforming radio.

[0006] To avoid having to increase the number of antennas at the cell site, the above-mentioned 5G base station antennas typically also include passive linear arrays that support traditional 2G, 3G, and / or 4G cellular services. In some cases, both active beamforming arrays and passive linear arrays can be included in a single base station antenna. Another solution for providing an antenna that supports 2G / 3G / 4G and 5G cellular services is to install a 5G active antenna module (i.e., a module that includes an active beamforming array and associated beamforming radio equipment) behind a passive base station antenna that includes one or more 2G, 3G, and / or 4G passive linear arrays. An opening is provided in the reflector of the passive base station antenna so that the antenna beam generated by the 5G active beamforming array can be transmitted through the passive base station antenna. This design is advantageous because the active antenna module can be removable, and therefore as enhanced 5G capabilities are developed, cellular operators can initially deploy only the passive base station antenna and add active antenna modules later, or can replace the initially deployed active antenna module with an upgraded active antenna module without having to replace the passive base station antenna. Herein, a base station antenna comprising a combination of a passive base station antenna with a rear mounted active antenna module may be referred to as a "passive / active antenna system."

[0007] Passive / active antenna systems may include frequency selective surfaces. Chinese patent application 114530675 discloses various frequency selective surfaces and base station antennas including such frequency selective surfaces. Summary of the Invention

[0008] According to an embodiment of the present invention, a base station antenna is provided, which includes an array of lower frequency band radiating elements, an array of higher frequency band radiating elements and a frequency selective surface having a plurality of unit cells, wherein the equivalent circuit of each unit cell includes a first parallel inductor-capacitor ("LC") circuit, and the first parallel inductor-capacitor circuit is embedded in a second parallel LC circuit.

[0009] In some embodiments, the first parallel LC circuit may be connected in series with the capacitor of the second parallel LC circuit. In some embodiments, a ratio of a first inductance of the first parallel LC circuit to a second inductance of the second parallel LC circuit may be between 0.5 and 2.0. In some embodiments, a ratio of a first capacitance of the first parallel LC circuit to a second capacitance of the second parallel LC circuit may be between 0.5 and 2.0.

[0010] In some embodiments, the array of lower frequency band radiating elements may be mounted in front of the frequency selective surface and the array of higher frequency band radiating elements mounted behind the frequency selective surface.

[0011] In some embodiments, a first unit cell in the unit cells may include a plurality of metal pads and a plurality of metal traces, the plurality of metal traces connecting each of the plurality of metal pads to all other metal pads in the plurality of metal pads. In some embodiments, each of the plurality of metal pads may be separated from at least one other metal pad in the plurality of metal pads by a serpentine gap. In some embodiments, each serpentine gap may have a periodic waveform shape. In some embodiments, the metal pad of the first unit cell in the unit cells may be separated from an adjacent unit cell by a gap. In some embodiments, the first unit cell in the unit cells may further include an outer metal ring surrounding the gap. In some embodiments, the outer metal ring may include a plurality of sides, and wherein each side of the outer metal ring is integral with a side of the outer metal ring of a corresponding unit cell adjacent to the first unit cell in the unit cells.

[0012] In some embodiments, a first unit cell of the unit cells may include a plurality of metal pads surrounded by a continuous gap extending around the perimeter of the metal pads, and each metal pad may be separated from at least one other of the metal pads by a serpentine gap. In some embodiments, the frequency selective surface may be implemented in a printed circuit board comprising a dielectric substrate and a metallization pattern on a first side of the dielectric substrate, and the metal pads may be part of the metallization pattern. In some embodiments, a plurality of openings may be provided in the metallization pattern, wherein the plurality of metal pads surround the openings. In some embodiments, the serpentine gap may extend from a first one of the openings to the continuous gap. In some embodiments, the openings may define a plurality of metal traces, the plurality of metal traces being part of the metallization pattern connecting each metal pad to the remaining metal pads. In some embodiments, when the base station antenna is installed for use, at least one of the metal traces may extend at a 45° angle, and another one of the metal traces may extend at a -45° angle.

[0013] In some embodiments, a first unit cell in the unit cells may include a first metal pad and a second metal pad, wherein the first metal pad has a first edge including a plurality of spaced-apart first metal protrusions, and the second metal pad is adjacent to the first metal pad and has a second edge including a plurality of spaced-apart second metal protrusions. In some embodiments, the second metal protrusions may intersect with the first metal protrusions.

[0014] According to an embodiment of the present invention, a base station antenna is provided, which includes an array of lower frequency band radiating elements, an array of higher frequency band radiating elements and a frequency selective surface having a plurality of unit cells, wherein each unit cell includes a plurality of metal pads, and each metal pad is capacitively coupled to two other metal pads and is current coupled to at least another metal pad of the metal pads via one or more metal traces among a plurality of metal traces.

[0015] In some embodiments, each metal pad of a first one of the unit cells may be capacitively coupled to two other metal pads of the first one of the unit cells through a pair of serpentine edge capacitors.

[0016] In some embodiments, the frequency selective surface may be implemented in a printed circuit board including a dielectric substrate, and each metal pad in a first one of the unit cells may be capacitively coupled to two other metal pads of the first one of the unit cells through the dielectric substrate.

[0017] In some embodiments, each unit cell may further include an outer metal ring surrounding the plurality of metal pads. In some embodiments, the outer metal ring of each unit cell may be integral with the outer ring of an adjacent unit cell.

[0018] In some embodiments, a first metal pad among the metal pads may include a first edge including a plurality of spaced-apart first metal protrusions, and a second metal pad adjacent to the first metal pad may include a plurality of spaced-apart second metal protrusions. In some embodiments, the second metal protrusions may intersect with the first metal protrusions.

[0019] In some embodiments, the frequency selective surface can be implemented in a printed circuit board, the printed circuit board comprising a dielectric substrate and a metallization pattern comprising the plurality of metal pads, wherein a plurality of openings are provided at the center of each unit cell, and the plurality of metal pads of each unit cell surround the plurality of openings of the unit cell. In some embodiments, the openings of each unit cell can define a plurality of metal traces of each unit cell.

[0020] In some embodiments, the equivalent circuit of each unit cell may be a first parallel LC circuit embedded within a second parallel LC circuit. In some embodiments, the first parallel LC circuit may be connected in series with a capacitor of the second parallel LC circuit.

[0021] According to an embodiment of the present invention, a base station antenna is provided, which includes an array of lower frequency band radiating elements, an array of higher frequency band radiating elements and a frequency selective surface having a plurality of unit cells, wherein a first unit cell in the unit cells includes a plurality of metal pads, wherein each metal pad is capacitively edge coupled to another metal pad in the metal pads through a corresponding serpentine gap in a plurality of serpentine gaps.

[0022] In some embodiments, each serpentine gap may have a periodic waveform shape.

[0023] In some embodiments, a first unit cell among the unit cells may further include an outer metal ring surrounding the metal pad, wherein the outer metal ring is separated from the metal pad by a gap providing no metal.

[0024] In some embodiments, each of the unit cells may include a plurality of metal pads and an outer metal ring surrounding the metal pads, and the outer metal ring of each unit cell may directly contact an outer metal ring of each adjacent unit cell.

[0025] In some embodiments, the frequency selective surface may be implemented in a printed circuit board comprising a dielectric substrate and a metallization pattern on a first side of the dielectric substrate.

[0026] In some embodiments, the serpentine gap may be a gap in the metallization pattern that exposes the dielectric substrate. In some embodiments, the metallization pattern includes a plurality of openings in the center of each unit cell, wherein the openings in the metallization pattern in each unit cell are surrounded by a plurality of metal pads of each corresponding unit cell. In some embodiments, a first unit cell in the unit cells may further include an outer metal ring separated from the metal pads of the first unit cell in the unit cells by a continuous gap. The serpentine gap may extend from the first opening in the metallization pattern of the first unit cell in the unit cells to the continuous gap.

[0027] In some embodiments, the equivalent circuit of each unit cell may be a first parallel LC circuit embedded within a second parallel LC circuit. In some embodiments, the first parallel LC circuit may be connected in series with a capacitor of the second parallel LC circuit.

[0028] In some embodiments, the array of lower frequency band radiating elements may be mounted in front of the frequency selective surface and the array of higher frequency band radiating elements may be mounted behind the frequency selective surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1Ais a schematic rear perspective view of a conventional passive / active antenna system including a passive base station antenna and an associated active antenna module.

[0030] Figure 1B It eliminates the need for the radome of the passive base station antenna and the radome and frequency selective surface of the active antenna module. Figure 1A Schematic perspective view of a conventional passive / active antenna system.

[0031] Figure 1C Can be included in Figure 1A Front view of a small portion of a conventional frequency selective surface used in a passive / active antenna system.

[0032] Figure 1D yes Figure 1C Front view of a single unit cell of a frequency selective surface, showing the non-negligible capacitive and inductive coupling for current flowing in the direction of the arrow.

[0033] Figure 1E It shows Figure 1C Circuit diagram of the equivalent circuit of the unit cell of the frequency selective surface.

[0034] Figure 2A is a schematic front view of a small portion of a frequency selective surface according to an embodiment of the present invention.

[0035] Figure 2B yes Figure 2A Schematic front view of a single unit cell of a frequency selective surface.

[0036] Figure 2C It shows Figure 2A A diagram showing the locations of various inductive and capacitive couplings present in a unit cell.

[0037] Figure 2D It shows Figures 2B-2C Circuit diagram of the equivalent circuit of the unit cell.

[0038] Figure 2E yes Figure 2B A greatly enlarged view of the interface between two of the metal pads included in the unit cell.

[0039] Figure 3 It shows Figures 1C-1D The rejection and transmission characteristics of the frequency selective surface are related to Figures 2A-2B Graph comparing the rejection and transmission characteristics of a frequency selective surface.

[0040] Figure 4A is a schematic front view of a unit cell of a frequency selective surface according to another embodiment of the present invention.

[0041] Figure 4B is a schematic front view of a portion of a complete unit cell and six additional unit cells of a frequency selective surface according to additional embodiments of the present invention.

[0042] Figure 4C is a schematic front view of a unit cell of a frequency selective surface according to some further embodiments of the present invention.

[0043] Figure 5A is a schematic front view of a unit cell of a frequency selective surface according to some additional embodiments of the present invention.

[0044] Figure 5B yes Figure 5A Schematic back view of the unit cell.

[0045] Figure 5C yes Figure 5A A shaded front view of the unit cell. DETAILED DESCRIPTION

[0046] Figures 1A-1B A conventional passive / active antenna system 100 is shown, which includes both a passive base station antenna 110 and an active antenna module 150. In particular, Figure 1A is a schematic rear perspective view of the passive / active antenna system 100 . Figure 1B The passive base station antenna 110 antenna cover and the active antenna module 150 antenna cover and frequency selective surface are omitted. Figure 1A A schematic perspective view of a passive / active antenna system 100 is shown. Figure 1A and Figure 1B , the axes show the vertical (V), horizontal (H), and forward (F) directions of the base station antenna system 100 .

[0047] refer to Figure 1AThe passive / active antenna system 100 can be mounted, for example, on an antenna tower 102 using mounting hardware 104. The passive / active antenna system 100 includes a passive base station antenna 110 and an active antenna module 150. The active antenna module 150 is mounted behind the passive base station antenna 110. The active antenna module 150 can be mounted directly on the rear surface of the passive base station antenna 110 or held in place behind the passive base station antenna 110 by mounting hardware 104, such as that used to mount the passive / active antenna system 100 on an antenna tower 102 (or other structure). The front surface of the passive / active antenna system 100 can face the antenna tower 102, facing the coverage area of ​​the passive / active antenna system 100. The passive base station antenna 110 includes a tubular radome 112 that surrounds and protects the antenna assembly mounted inside the radome 112. A top end cap 114 covers the top opening in the radome 112, and a bottom end cap 116 covers the bottom opening in the radome 112. A plurality of RF ports 118 extend through the bottom end cap 116 and are used to connect the passive base station antenna 110 to one or more external radio devices (not shown). An active antenna module 150 can be removably mounted behind the passive base station antenna 110 so that the active antenna module 150 can be later replaced with a different active antenna module, preferably without removing the passive base station antenna 110 from the antenna tower 102. The active antenna module 150 is referred to as being "associated with" the passive base station antenna 110 because it is mounted directly behind the passive base station antenna 110 and is configured to transmit and receive RF signals through the passive base station antenna 110.

[0048] refer to Figure 1B , the passive base station antenna 110 includes a reflector assembly 120 and a plurality of passive linear arrays of radiating elements extending forward from the passive reflector assembly 120. The linear arrays may support, for example, 3G and / or 4G cellular services. Figures 1A-1BIn the exemplary passive base station antenna 110 shown, the linear arrays include a first low-band linear array and a second low-band linear array 130-1, 130-2 configured to operate in all or part of the 617-960 MHz frequency band. Each low-band linear array 130 includes a vertically extending column of low-band radiating elements 132. The passive base station antenna 110 also includes first through fourth mid-band linear arrays 140-1 through 140-4 configured to operate in all or part of the 1427-2690 MHz frequency band. Each mid-band linear array 140 includes a vertically extending column of mid-band radiating elements 142. Each of the low-band linear array and the mid-band linear array 130, 140 is a passive linear array that generates a static antenna beam that provides coverage to a predefined coverage area (e.g., an antenna beam that is each configured to cover a sector of a base station), wherein only the coverage area changes when the electronic downtilt angle of the generated antenna beam is adjusted (e.g., to change the size of the cell).

[0049] Each of the low-band and mid-band radiating elements 132 and 142 can be implemented as a dual-polarization radiating element, comprising a first radiator and a second radiator that transmit and receive RF energy with orthogonal polarizations. When such dual-polarization radiating elements are used, each of the low-band and mid-band linear arrays 130 and 140 can be connected to a pair of RF ports 118. The first RF port 118 is connected between a first port of a radio device (e.g., a remote radio head mounted on an antenna tower 102 near a passive base station antenna 110) and the first polarization radiator of the radiating element in the linear array, and the second RF port 118 is connected between a second port of the radio device and the second polarization radiator of the radiating element in the linear array. The RF signal transmitted by the selected one of the linear arrays 130, 140 is passed from the radio device to one of the RF ports 118, and from the RF port 118 to a power splitter (or, alternatively, a phase shifter assembly including a power splitter), which splits the RF signal into a plurality of sub-components, which are fed to corresponding first radiators or second radiators of the radiating elements in the linear array so that the sub-components are radiated into free space.

[0050] The passive reflector assembly 120 includes a main reflector 122 and first and second spaced-apart reflector strips 124-1 and 124-2 extending vertically from respective first and second opposing sides of the main reflector 122. The passive reflector assembly 120 may also include a third reflector strip 124-3 extending horizontally between the first and second reflector strips 124-1 and 124-2. An opening 126 is defined between the first and second reflector strips 124-1 and 124-2. For example, the opening 126 may be defined by the top portion of the main reflector 122, the first and second reflector strips 124-1 and 124-2, and the third reflector strip 124-3. Most of the low-band and mid-band radiating elements 132 and 142 are mounted to extend forward from the main reflector 122. However, the low-band linear arrays 130-1, 130-2 and the mid-band linear arrays 140-1, 140-4 each extend substantially the full length of the passive / active antenna system 100 and, therefore, extend beyond the main reflector 122. The first and second reflector strips 124-1, 124-2 provide mounting locations for the low-band and mid-band radiating elements 132, 142 positioned above the main reflector 122. The first and second reflector strips 124-1, 124-2 can be integral with the main reflector 122 so that the first, second reflector strips 124-1, 124-2, and the main reflector 122 are maintained at a common ground voltage, which can be important for the performance of the linear arrays 130-1, 130-2, 140-1, 140-4.

[0051] Each low-band radiating element 132 may include a tilted -45° / +45° cross-dipole radiating element including a -45° dipole radiator 134-1 and a +45° dipole radiator 134-2, the dipole radiators being arranged to form a cross when viewing the radiating element 132 from the front. The dipole radiators 134 may (but need not) extend in a plane parallel to the plane defined by the main reflector 122. Each mid-band radiating element 142 may similarly include a tilted -45° / +45° cross-dipole radiating element including a -45° dipole radiator and a +45° dipole radiator.

[0052] The dipole radiators 134-1, 134-2 can be mounted on feed stems (not visible in the figure) of the radiating element 132. The feed stems transfer RF signals between the dipole radiators and the associated feed network. Conventionally, cross-dipole radiating elements extend forward from the main reflector surface of the reflector assembly, wherein the feed stems of the radiating elements extend perpendicular to the main reflector surface. The radiating elements 132 extending forward from the main reflector 122 can have a conventional design, wherein the feed stems extend perpendicular to the main reflector 122. However, the low-band radiating elements 132 mounted on the first and second reflector strips 124-1, 124-2 have so-called "tilted" feed stems 136 that extend forward from the reflector strips 124-1, 124-2 at an inclined angle. In particular, the base of each feed stem is mounted on one of the reflector strips 124 - 1 , 124 - 2 , and the feed stems extend at an angle such that the center of the cross defined by the dipole radiators 134 - 1 , 134 - 2 is above the opening 126 .

[0053] The active antenna module 150 includes a multi-column beamforming array 160 of radiating elements 162 and a beamforming radio (not visible in the figure). The multi-column beamforming array 160 can be mounted behind the front radome of the active antenna module 150 (at Figure 1B (The radome of active antenna module 150 is omitted to reveal beamforming array 160, and a beamforming radio can be mounted behind the multi-column beamforming array 160. Beamforming array 160 may, for example, include multiple vertically extending columns of high-band radiating elements 162 configured to operate in all or part of the 3.1-4.2 GHz frequency band. High-band radiating elements 162 are mounted to extend forward from reflector 154 of active antenna module 150. The beamforming radio can electronically adjust the amplitude and / or phase of sub-components of the RF signal output to different radiating elements 162 of multi-column beamforming array 160. For example, each port of the beamforming radio can be coupled to a column of radiators in beamforming array 160, and the amplitude and phase of the sub-components of the RF signal fed to the radiators in each column can be adjusted so that the generated antenna beam is narrowed in the azimuth plane and pointed in a desired direction in the azimuth plane.

[0054] like Figure 1B As shown in FIG, the beamforming array 160 of the active antenna module 150 is mounted behind the opening 126 in the passive reflector assembly 120. The beamforming array 160 is Figure 1B It can be seen in Figure 1B1. The radomes of both the passive base station antenna 110 and the active antenna module 150 are removed in the view of FIG. 1. The opening 126 in the passive reflector assembly 120 allows the antenna beam generated by the beamforming array 160 to pass through the passive base station antenna 110 and exit the front of the radome 112 of the passive base station antenna 110 to provide service to the coverage area of ​​the passive / active antenna system 100.

[0055] The opening 126 in the passive reflector assembly 120 is covered by a frequency selective surface 128. Figure 1B The frequency selective surface 128 is omitted in FIG. 1 to illustrate the beamforming array 160 positioned behind the frequency selective surface 128, but in FIG. Figure 1B 1 includes a dashed box showing where the frequency selective surface 128 will be mounted. As shown by the dashed box, the frequency selective surface 128 can extend across and / or cover the opening 126 in the passive reflector assembly 120. The frequency selective surface 128 can be mounted, for example, in front of, behind, or flush with the opening 126 in the passive reflector assembly 120.

[0056] Depending on the frequency of the RF energy, the frequency selective surface 128 can act as a spatial filter that passes, substantially attenuates, and / or reflects the RF energy. Frequency selective surfaces are known in the art and typically include a grid pattern of unit cells, such as a grid pattern of metal patches and / or other metal structures that form a resonant circuit. The metal patches / structures can be arranged in one or more layers. The frequency selective surface 128 can be implemented, for example, as a metal sheet having a grid structure stamped or otherwise formed therein, or as a dielectric substrate (e.g., a printed circuit board) having one or more metal patterns formed therein. The frequency selective surface 128 can be configured to substantially pass RF energy within a first frequency range incident thereon (here, the first frequency range may include the operating frequency band of the radiating elements included in the multi-column array 160), while partially or substantially not passing (e.g., reflecting) RF energy within a second frequency range incident thereon (here, the second frequency range may include the operating frequency band of the radiating elements included in the passive base station antenna 110). Examples of frequency selective surfaces are discussed in US Pat. No. 11,482,774 to Hou et al., which is incorporated herein by reference in its entirety.

[0057] Figure 1C is a front view of a representative small portion of a conventional frequency selective surface 200 that can be used to implement Figure 1A The frequency selective surface 128 in the passive / active antenna system of FIG. The frequency selective surface 200 has a unit cell structure in which a large number of (usually) identical unit cells 220 form the frequency selective surface 200. Figure 1CThe view of FIG2 shows six unit cells 220 of the frequency selective surface 200. It will be appreciated that the frequency selective surface 200 will typically include hundreds or thousands of unit cells 220 because the individual unit cells 220 are very small and the openings 126 are typically quite large.

[0058] Each unit cell 220 may be a "sub-wavelength" structure, meaning that the major dimension of each unit cell 220 is smaller than Figure 1A The wavelength of the RF signal transmitted and received by the conventional passive / active antenna system 100 is 1 / 4 of the wavelength of the conventional passive / active antenna system 100. Generally, the major dimension of each unit cell 220 is about 1 / 3 to 1 / 4 or less of the wavelength corresponding to the center frequency of the operating frequency range of the high-band radiating element 162. The unit cell 220 may have capacitive coupling and inductive coupling formed therein, which are designed to function as a spatial filter that allows RF energy within a certain frequency range incident on the frequency selective surface 200 to pass therethrough with minimal attenuation, while substantially reflecting RF energy in other frequency bands.

[0059] like Figure 1C As shown in FIG, each unit cell 220 has a square shape when viewed from the front (or back). The unit cells 220 are formed in a printed circuit board 210, which includes a dielectric substrate 212 and a metallization pattern formed on the dielectric substrate 212. The metallization pattern includes first to fourth metal pads 230-1, 230-4 formed in four quadrants of the square. Each metal pad 230 of a first unit cell 220 is combined with the metal pads 230 of three adjacent unit cells 220 to produce a larger metal pad 240. Four T-shaped regions or "openings" 270-1 to 270-4 are provided, where the openings 270 are areas where no metal is provided. The openings 270 are radially located around the center of each unit cell 220. The metal-free T-shaped openings 270 do not extend all the way to the edges of the unit cell 220, resulting in four narrow traces 280, each of which galvanically connects the large metal pads 240 to one another.

[0060] Each unit cell 220 includes multiple different non-negligible capacitive and inductive couplings. Figure 1D is a front view of a single unit cell 220, which shows the Figure 1D The capacitive coupling and inductive coupling of the current flowing in the direction of the arrow in the figure cannot be ignored. Figure 1D As shown in FIG, a first capacitive coupling 202A is formed across the opening 270-4 between the facing edges of the metal pad 230-1 and the metal pad 230-4. Similarly, a second capacitive coupling 202B is formed across the opening 270-2 between the facing edges of the metal pad 230-2 and the metal pad 230-3. Figure 1D Also shown in the figure, “vertical” (in Figure 1DThe narrow trace 280 provided in FIG. 2 (in the view of FIG. 2 ) forms the first and second inductors 204A, 204B. As can be seen, each inductor 204A, 204B is electrically coupled in parallel to a corresponding capacitor 202A, 202B.

[0061] Figure 1E It shows Figure 1D FIG2 is a circuit diagram of an equivalent circuit of a unit cell 220. Given the symmetry of the unit cell 220, the two capacitors 202A, 202B can be considered as a single larger capacitor 202. Similarly, due to the symmetry, the two inductors 204A, 204B can be considered as a single larger inductor 204. Therefore, as Figure 1E As shown in , the equivalent circuit of the unit cell 220 includes a first capacitor 202 electrically arranged in parallel with a first inductor 204 .

[0062] According to embodiments of the present invention, passive / active antenna systems with improved frequency selective surfaces are provided. These frequency selective surfaces can be mounted in the passive / active antenna system behind a lower-band array of radiating elements and in front of a higher-band array of radiating elements. The lower-band array of radiating elements can be, for example, a 2G / 3G / 4G linear array of low-band or mid-band radiating elements, while the higher-band array of radiating elements can be a multi-column beamforming array of higher-band radiating elements. The improved frequency selective surfaces disclosed herein can improve selectivity in both the higher and lower frequency bands, thereby improving the performance of higher-band active beamforming arrays and, for example, passive mid-band linear arrays included in the passive / active antenna system. For example, one of the disclosed frequency selective surfaces can provide approximately 0.2 dB of directivity improvement for a mid-band linear array and approximately 0.4 dB of directivity improvement for a high-band array, compared to state-of-the-art conventional frequency selective surfaces. These improvements are provided because frequency selective surfaces according to embodiments of the present invention can exhibit improved reflectivity within the mid-band frequency range and improved transparency within the higher-band frequency range.

[0063] In some embodiments, a unit cell of a frequency selective surface may have an equivalent circuit comprising a first parallel inductor-capacitor ("LC") circuit embedded within a second parallel LC circuit. The first parallel LC circuit may be connected in series with the capacitor of the second parallel LC circuit. In some embodiments, a first capacitance of the first parallel LC circuit may be between 0.5 and 2.0 times the second capacitance of the second parallel LC circuit, and / or a first inductance of the first parallel LC circuit may be between 0.5 and 2.0 times the second inductance of the second parallel LC circuit.

[0064] In some embodiments, a frequency selective surface is provided having a plurality of unit cells, wherein each unit cell includes a plurality of metal pads. The metal pads in each unit cell can be arranged radially around a central portion of the unit cell so that each metal pad in the unit cell has two adjacent metal pads. Adjacent metal pads can be capacitively coupled to each other. In some embodiments, adjacent metal pads can be capacitively edge coupled to each other across a serpentine gap to form a serpentine edge capacitance, as will be described in more detail herein. The edges of adjacent metal pads may have, for example, a periodic waveform shape (e.g., a square waveform shape, a triangular waveform shape, a sinusoidal waveform shape, etc.), and the peaks of the waves may intersect with each other to form a serpentine gap. In other embodiments, adjacent metal pads can be capacitively coupled to each other by forming adjacent metal plates on opposing surfaces of a dielectric substrate (e.g., a dielectric substrate of a printed circuit board) and overlapping the metal plates to a certain extent so that they are capacitively coupled to each other through the dielectric substrate.

[0065] In some embodiments, the plurality of metal traces may connect each of the plurality of metal pads to some or all of the other metal pads in the plurality of metal pads. The metal pad of each unit cell may be separated from adjacent unit cells by a gap. In addition, each of the unit cells may further include an outer metal ring surrounding the gap, wherein the outer metal ring defines the periphery of the unit cell. The outer metal ring of each unit cell may directly contact and be integral with the outer metal ring of each unit cell adjacent to the unit cell.

[0066] Each unit cell may include a plurality of openings that are not provided with metal. The metal pads of the unit cell may radially surround these openings. In a unit cell that includes one or more serpentine gaps, the serpentine gaps may extend from corresponding ones of the openings to a continuous gap that separates the metal pads from the outer metal ring. The openings that are not provided with metal may define metal traces that connect each metal pad to the other ones of the metal pads.

[0067] The frequency selective surface disclosed herein can, for example, be incorporated into a passive base station antenna. The passive base station antenna can be combined with an active antenna module to provide a passive / active antenna system according to an embodiment of the present invention. The passive base station antenna can include an array of lower-band radiating elements, such as an array of low-band radiating elements configured to operate in some or all of the 617-960 MHz frequency band and / or an array of mid-band radiating elements configured to operate in some or all of the 1427-2690 MHz frequency band. The active antenna module can include a beamforming array of higher-band radiating elements, such as an array of high-band radiating elements configured to operate in some or all of the 3700-3980 MHz frequency band. The beamforming array of higher-band radiating elements can be mounted behind the frequency selective surface, and the frequency selective surface can be configured to be substantially transparent in the operating frequency band of the beamforming array of higher-band radiating elements. The array of lower-band radiating elements may be mounted in front of the frequency selective surface, and the frequency selective surface may be configured to be substantially reflective in an operating frequency band of the array of lower-band radiating elements.

[0068] Now refer to Figures 2A-5C Examples of frequency selective surfaces that may be used in passive / active antenna systems according to embodiments of the present invention are discussed in more detail.

[0069] Figure 2A is a schematic front view of a small portion of a frequency selective surface 300 according to an embodiment of the present invention. Figure 2B yes Figure 2A FIG. 1 is an enlarged view of one of the unit cells 320 of the frequency selective surface 300 . Figure 2C It shows Figure 2B A schematic diagram of the locations of various inductive and capacitive couplings within the unit cell 320, and Figure 2D is a circuit diagram showing an equivalent circuit of the unit cell 320. Finally, Figure 2E is a greatly enlarged view of the interface between two metal pads included in unit cell 320 .

[0070] First reference Figure 2A The frequency selective surface 300 is formed on a printed circuit board 310, which includes a dielectric substrate 312 having a first metallization pattern formed thereon. The frequency selective surface 300 includes a large number of unit cells 320 arranged in a plurality of rows and columns. Figure 2A The dashed box in identifies the extent of one of the unit cells 320.

[0071] refer to Figure 2B, each unit cell 320 includes four metal pads 330-1 to 330-4. The four metal pads 330 are positioned directly adjacent to each other in two columns and two rows, such that the outer perimeter of the combination of the four metal pads 330 defines a larger square 340. The metal pads 330 are arranged radially around the central portion of the unit cell 320 so that one of the metal pads 330 is adjacent to each metal pad 330 in the other two adjacent unit cells 320. Each metal pad 330 has a generally square shape, except that a small square of metal is omitted from the inner corners of each metal pad 330. The two outer sides 332 of each metal pad 330 are straight sides, while each inner side 332 of the metal pad 330 includes a plurality of spaced-apart metal protrusions 334 separated by recesses 336, as shown in FIG. Figure 2E , which is a greatly enlarged view of the interface between two metal pads 330. The spaced-apart metal protrusions 334 along the inner side 332 of each metal pad 330 interdigitate with the spaced-apart metal protrusions 334 along the inner side 332 of an adjacent metal pad 330, meaning that the protrusions 334 of the inner side 332 of a first metal pad 330 are received within corresponding recesses 336 in the inner side 332 of a second (adjacent) metal pad 330. The adjacent inner sides 332 of adjacent metal pads 330 are spaced apart from each other by small gaps 338, such that the inner sides 332 of a metal pad 330 do not directly contact the inner sides 332 of an adjacent metal pad 330. These gaps 338 are serpentine gaps, meaning they do not extend in a straight line, but rather undulate gaps 338 that extend back and forth to increase the overall length of the gaps 338 (where the overall length of the gaps 338 is equal to the length of the gaps 338 if they were "pulled" into a straight line). Thus, each metal pad 330 of the unit cell 320 is capacitively coupled to two adjacent metal pads 330 across a corresponding serpentine gap 338. This capacitive coupling is edge capacitive coupling, as the coupling occurs primarily from the edge of one metal pad 330 to the edge of an adjacent metal pad 330. Thus, a "serpentine edge capacitor" is formed between the inner sides 332 of each pair of adjacent metal pads 330 in the unit cell 320. As used herein, the term "serpentine edge capacitor" refers to a capacitor formed between facing edges of two metal structures, where the length of the edge capacitor is at least 1.5 times the linear length of the area where the facing edges overlap.

[0072] Still refer to Figure 2B Unit cell 320 further includes an outer metal ring 350 having an annular square shape. Outer metal ring 350 surrounds four metal pads 330-1 to 330-4. Gap 360 separates outer metal ring 350 from metal pads 330. Metal pads 330 are capacitively coupled to outer metal ring 350 across gap 360. Gap 360 may be a continuous gap extending all the way around the four metal pads 330.

[0073] Four "openings" 370 are provided in the center portion of each unit cell 320 in the metallization pattern of the printed circuit board 310. These openings 370 refer to locations where no metal is provided (thus exposing the dielectric substrate 312). Each opening 370 has a triangular shape. The openings 370 are separated from each other by first to fourth metal traces 380, which are part of the metallization pattern on the dielectric substrate 312. The four metal traces 380 connect at least some of the four metal pads 330 to other metal pads in the metal pads 330 in a galvanic manner. Since the metal traces 380 have a narrow width (e.g., less than 25% of the average width of the metal pads 330), they exhibit high inductance. As Figure 2B As best seen in FIG, each serpentine gap 338 may extend from a corresponding one of the openings 370 to the continuous gap 360 .

[0074] Figure 2C is a schematic front view of the unit cell 320, with capacitor and inductor symbols added to illustrate the inductive and capacitive coupling within the unit cell 320. Figure 1C Same as in Figure 2C , capacitive coupling and inductive coupling are shown only for currents flowing in the directions of the arrows to simplify the discussion.

[0075] like Figure 2C As shown in FIG, serpentine gap 338-4 forms a first capacitive coupling 302A between metal plates 330-1 and 330-4, and serpentine gap 338-2 forms a second capacitive coupling 302B between metal plates 330-2 and 330-3. Furthermore, capacitive couplings 306A-306D are formed between outer metal ring 350 and respective metal pads 330-1 to 330-4 across continuous gap 360. The "vertical" extensions of outer metal ring 350 are narrow metal traces that form respective inductors 308A, 308B, and narrow metal trace 380 forms an inductive coupling between metal pads 330-1 and 330-3, while the other two metal traces of narrow metal traces 380 form inductive couplings 304A, 304B between metal pads 330.

[0076] Figure 2D It shows Figure 2C The circuit diagram of the equivalent circuit of the unit cell 320 is shown in FIG. Figure 2D As shown in FIG, given the symmetry of the unit cell 320, the two capacitive couplings 302A, 302B can be considered as a single larger capacitive coupling 302. Similarly, due to the symmetry, the two inductive couplings 304A, 304B can be considered as a single larger inductive coupling 304. The capacitive couplings 302A, 302B are electrically arranged in parallel with the inductive couplings 304A, 304B, and thus as shown in FIG. Figure 1EAs shown in FIG, the equivalent circuit of the unit cell 200 includes a first capacitive coupling 302 electrically connected in parallel with a first inductive coupling 304, which together form a first parallel inductor-capacitor ("LC") circuit 305. Given the symmetry of the unit cell 320, the four capacitive couplings 306A-306D can be combined into a single capacitive coupling 306. Figure 2C As best seen in FIG, the capacitive couplings 306A-306D are electrically connected in series with the first parallel LC circuit 305. The two inductive couplings 308A, 308B can also be combined into a single (larger) inductive coupling 308, which is placed in parallel with the capacitive coupling 306 to form a second parallel LC circuit 309. Figure 2D As shown in FIG, the first parallel LC circuit 305 is embedded in the second parallel LC circuit 309.

[0077] The frequency selective surface 300 may be used in various base station antennas, including, for example Figures 1A-1B In the passive / active antenna system 100 of the present invention, the frequency selective surface 300 can be used in place of the conventional frequency selective surface 128 to provide a base station antenna according to an embodiment of the present invention. For example, the frequency selective surface 300 can be installed in the passive base station antenna 110 behind the opening 126 in the reflector assembly 120.

[0078] Figure 3 It shows Figures 1C-1D The rejection and transmission characteristics of the frequency selective surface 200 are Figures 2A-2B The rejection and transmission characteristics of the frequency selective surface 300 are compared in FIG. Figure 3 The dashed curve shows Figures 1C-1D The S11 (reflectivity) and S21 (transmittance) performance of the frequency selective surface 200 are shown in FIG. Figures 2A-2B The S11 (reflectivity) and S21 (transmittance) performance of the frequency selective surface 300 are shown in FIG. The frequency selective surface 300 is designed to be used in a passive / active antenna system, the passive / active antenna system including: a passive base station antenna having a low-band array configured to operate in the 696-960 MHz frequency band and a mid-band array configured to operate in the 1695-2360 MHz frequency band; and an active antenna module including a multi-column beamforming array configured to operate in the 3.7-4.0 GHz (approximately) frequency band.

[0079] like Figure 3 As shown in FIG, the S11 performance (i.e., the amount of reflection) of the frequency selective surface 300 is greater than or equal to (i.e., less reflective) than the S11 performance of the frequency selective surface 200 over the entire 3.7-4.0 GHz frequency band. This indicates that the frequency selective surface 300 will reflect less high-band RF radiation. Although Figure 3 It is difficult to see in the S21 curve of , but simulations indicate that the reduced amount of reflections increases the directivity of the high-band array by about 0.2dB. Figure 3 As can be seen, the S11 performance of the frequency selective surface 300 in the 1695-2360 MHz band is significantly improved compared to the S11 performance of the frequency selective surface 200 across the entire 1695-2360 MHz band. This improved performance results in an approximately 0.4 dB increase in directivity for the mid-band array. Thus, it can be seen that frequency selective surfaces according to embodiments of the present invention can provide significant performance improvements.

[0080] Figures 2A-2D The frequency selective surface 300 may be used in a base station antenna according to an embodiment of the present invention. The base station antenna may be, for example, a passive / active base station antenna system 100, which includes a passive base station antenna 110 having an active antenna module 150 mounted thereon. The base station antenna 100 may include an array of lower frequency band radiating elements 130 / 140 and an array of higher frequency band radiating elements 160. The array of lower frequency band radiating elements 130 / 140 may be mounted in front of the frequency selective surface 300, and the array of higher frequency band radiating elements 160 may be mounted behind the frequency selective surface 300. The frequency selective surface 300 may include a plurality of unit cells 320, and the equivalent circuit of each unit cell 320 may include a first parallel LC circuit 305 embedded in a second parallel LC circuit 309, as shown in FIG. Figure 2D In addition, the first parallel LC circuit 305 can be electrically connected in series with the capacitor 306 of the second parallel LC circuit 309.

[0081] In an exemplary embodiment, the ratio of the first inductance 304 of the first parallel LC circuit 305 to the second inductance 308 of the second parallel LC circuit 309 can be between 0.5 and 2.0. In some embodiments, the ratio of the first capacitance 302 of the first parallel LC circuit to the second capacitance of the second parallel LC circuit 309 can be between 0.5 and 2.0.

[0082] In an exemplary embodiment, a first unit cell among unit cells 320 may include a plurality of metal pads 330 and a plurality of metal traces 380 connecting each metal pad 330 to at least some of the other metal pads 330. Furthermore, in the first unit cell among unit cells 320, each metal pad 330 may be separated from at least one other metal pad among metal pads 330 by a serpentine gap 338. For example, a first metal pad among metal pads 330-1 may have a first edge 332 including a plurality of spaced-apart first metal protrusions 334, and a second metal pad among metal pads 330-2, adjacent to the first metal pad among metal pads 330-1, may have a second edge 332 including a plurality of spaced-apart second metal protrusions 334. The second metal protrusions 334 may intersect with the first metal protrusions 334 to form a serpentine gap 338. In some cases, each of these serpentine gaps 338 may have a periodic waveform shape. The metal pad 330 of a first unit cell among the unit cells 320 may be separated from a unit cell 320 of an adjacent first unit cell among the unit cells 320 by a continuous gap 360. In addition, the first unit cell among the unit cells 320 may further include an outer metal ring 350 surrounding the continuous gap 360. The outer metal ring 350 may define a perimeter of the first unit cell among the unit cells 320. The outer metal ring 350 may have a plurality of sides, wherein each side is integral with a side of the outer metal ring 350 of a corresponding unit cell 320 of the adjacent first unit cell 320, such that two (integral) outer rings 350 are disposed between adjacent gaps 360.

[0083] In other embodiments, a base station antenna 100 is provided that includes an array of lower-band radiating elements 130 / 140, an array of higher-band radiating elements 160, and a frequency selective surface 300. The frequency selective surface 300 includes a plurality of unit cells 320, wherein each unit cell 320 includes a plurality of metal pads 330, and each metal pad 330 is capacitively coupled to two other metal pads in the metal pads 330 and galvanically coupled to at least one other metal pad in the metal pads 330 via one or more metal traces in the plurality of metal traces 380. As discussed above, the metal pads 330 can be capacitively coupled to each other using serpentine edge capacitors 338.

[0084] In yet other embodiments, a base station antenna 100 is provided, comprising an array of lower-band radiating elements 130 / 140, an array of higher-band radiating elements 160, and a frequency selective surface 300 having a plurality of unit cells 320. A first unit cell in the unit cells 320 comprises a plurality of metal pads 330, wherein each metal pad 330 is capacitively edge-coupled to another metal pad in the metal pads 330 via a corresponding serpentine gap in a plurality of serpentine gaps 338. Each serpentine gap 338 may have, for example, a periodic waveform shape. In some embodiments, the frequency selective surface 300 may be implemented in a printed circuit board 310 comprising a dielectric substrate 312 and a metallization pattern on a first side of the dielectric substrate 312. The metal pads 330 may be part of the metallization pattern, and the metallization pattern may further comprise an outer metal ring 350 surrounding the metal pads 330, wherein the outer metal ring 350 of each unit cell 320 directly contacts the outer metal ring 350 of each unit cell 320 that borders the first unit cell 320. A gap 360, where no metal is provided, may be provided between outer metal ring 350 and metal pad 330. Gap 360 may be a continuous gap 360, exposing dielectric substrate 312 of printed circuit board 310. A plurality of openings 370 are provided in the center of a first unit cell in unit cells 320 in the metallization pattern. Metal pad 330 may be positioned radially outside of opening 370 and may surround opening 370. Narrow metal traces 380, which are part of the metallization pattern, may be defined between openings 370.

[0085] It should be understood that Figures 2A-2E The frequency selective surface 300 is merely an exemplary frequency selective surface, and embodiments of the present invention are not limited thereto. Figures 4A-4C and Figures 5A-5C Four additional exemplary frequency selective surfaces are shown that may also provide improved performance according to embodiments of the present invention.

[0086] Figure 4A FIG4 is a schematic front view of a unit cell 420 of a frequency selective surface 400 according to another embodiment of the present invention. The frequency selective surface 400 can be implemented in a printed circuit board 410, which includes a dielectric substrate 412 having a first metallization pattern formed thereon. Although only a single unit cell 420 of the frequency selective surface 400 is shown in FIG4 , it should be understood that the frequency selective surface 400 includes a large number of unit cells 420. Similar to the unit cell 320, the unit cell 420 includes four metal pads 430-1 to 430-4, which are arranged such that the outer perimeter of the combination of the four metal pads 430 defines a larger square 440.

[0087] Four openings 470 are provided in the metallization pattern in the central region of the unit cell 420. The openings 470 are areas where metal is omitted, exposing the dielectric substrate 412. Each metal pad 430 generally has a truncated triangular shape, as two of the openings 470 serve to truncate the inner vertices of the triangle defined by each metal pad 430. The two outer sides 432 of each metal pad 430 are straight sides, while the two inner sides 432 of the metal pads 430 each include a plurality of spaced-apart metal protrusions that intersect with the spaced-apart metal protrusions provided along the inner sides 432 of adjacent metal pads 430. A small serpentine gap 438 is maintained between the two metal pads 430, such that a serpentine edge capacitor is formed between the two metal pads 430.

[0088] Similar to unit cell 320, unit cell 420 also includes a square outer metal ring 450 surrounding four metal pads 430. Metal pads 430 are separated from outer metal ring 450 by continuous gaps 460. Openings 470 in the metallization pattern of printed circuit board 410 each have a square shape and are separated from each other by first to fourth narrow metal traces 480 that galvanically connect the four metal pads 430 to each other. Serpentine gaps 438 extend from corresponding openings in openings 470 to continuous gaps 460. Unit cell 420 can have the same equivalent circuit as unit cell 320 and can function in the same manner as unit cell 320.

[0089] Figure 4B is a schematic front view of a complete unit cell 520 and a portion of six additional unit cells 520 of a frequency selective surface 500 according to an additional embodiment of the present invention. Unit cell 520 is similar to unit cells 320 and 420, but unit cell 520 has a hexagonal shape rather than a square shape. Thus, each unit cell 520 includes six metal pads 530 (rather than four) and similarly includes six openings 570 and six narrow metal traces 580. Outer metal ring 550 has a hexagonal shape, as does continuous gap 560. Unit cell 520 can have an equivalent circuit similar to that of unit cell 320, except that the equivalent circuit of unit cell 520 includes additional capacitance and inductive coupling due to the larger number of metal pads 530 and narrow metal traces 580. Unit cell 520 can function in the same manner as unit cell 320.

[0090] Figure 4Cis a schematic front view of a complete unit cell 620 and a portion of six additional unit cells 620 of a frequency selective surface 600 according to yet further additional embodiments of the present invention. Unit cell 620 is similar to unit cell 520, but has an octagonal shape. Thus, unit cell 620 includes eight metal pads 630, eight openings 670, and eight narrow metal traces 680. Outer metal ring 650 has an octagonal shape, as does continuous gap 660. Unit cell 620 may have an equivalent circuit similar to that of unit cell 520, except that the equivalent circuit of unit cell 620 includes additional capacitive and inductive coupling due to the larger number of metal pads 630 and narrow metal traces 680. Because it is not possible to "pack" unit cells 620 so that each side of a first unit cell 620 abuts a side of another unit cell 620, a plurality of additional metal pads 690 positioned between each group of four unit cells 620 are provided. These additional metal pads 690 may have a square shape.

[0091] The above-mentioned frequency selective surfaces each comprise a single metallization pattern and can therefore be implemented on a printed circuit board having a metallized dielectric substrate on only one side thereof.According to a further embodiment of the invention, a frequency selective surface comprising more than one metallization pattern is provided. Figures 5A-5C A unit cell 720 of one such frequency selective surface 700 is shown. In particular, Figure 5A is a schematic front view of the unit cell 720, Figure 5B is a schematic rear view of the unit cell 720, and Figure 5C is a shaded front view of unit cell 720. Figure 5C In the hatched diagram of FIG. 1 , the metallization pattern provided on the front side of the printed circuit board is shown using solid lines, whereas the metallization pattern provided on the back side of the printed circuit board is shown using dotted lines.

[0092] like Figures 5A-5C As shown in , the frequency selective surface 700 is implemented in a printed circuit board 710 comprising a dielectric substrate 712 having a first metallization pattern 714 on its front side and a second metallization pattern 716 on its back side. The unit cell 720 has a square shape.

[0093] First reference Figure 5A, the front metallization pattern 714 includes first and second metal pads 730-1 and 730-2 interconnected by a first narrow metal trace 780-1, and an outer metal ring 750 having a circular square shape. The first and second metal pads 730-1 and 730-2 are located in the upper right and lower left quadrants of the square defined by the unit cell 720. The outer metal ring 750 defines the perimeter of the unit cell 720 and is separated from the first and second metal pads 730-1 and 730-2 by a gap 760, such that the first and second metal pads 730-1 and 730-2 are capacitively coupled to the outer metal ring 750.

[0094] Next reference Figure 5B , the rear metallization pattern 716 includes a third metal pad and a fourth metal pad 730-3, 730-4 interconnected by a second narrow metal trace 780-2. When the unit cell 720 is viewed from the front, the third metal pad and the fourth metal pad 730-3, 730-4 are located in the upper left quadrant and the lower right quadrant of the square defined by the unit cell 720 (see Figure 5C In the depicted embodiment, the outer metal ring 750 does not overlap the third and fourth metal pads 730-3, 730-4. However, in other embodiments, the third and fourth metal pads 730-3, 730-4 can extend closer to the edge of the unit cell 720 so that they overlap the gap 760 (in this article, two metal structures on a printed circuit board "overlap" if an axis perpendicular to the dielectric substrate of the printed circuit board can be drawn as extending through the two elements), which serves to increase the capacitive coupling between the third and fourth metal pads 730-3, 730-4 and the outer metal ring 750. The first and second narrow metal traces 780-1, 780-2 are galvanically connected to each other via metal plated through holes 782 extending through the dielectric substrate 712.

[0095] refer to Figure 5C , it can be seen that the unit cell 720 is similar to Figures 2A-2D The unit cell 320 of the frequency selective surface 300 is shown in FIG. 3 , with the main difference being that metallization is implemented on both sides of the dielectric substrate 712 in the unit cell 720. The unit cell 720 also does not include the serpentine gap 338 included in the unit cell 320 because the metal pads 730 formed on opposite sides of the dielectric substrate 712 overlap to a certain extent to provide a desired amount of capacitive coupling between adjacent metal pads in the metal pads 730 (where “adjacent” means that the pads are on opposite sides of the dielectric substrate 712). Figure 5C). The narrow metal trace 780 in unit cell 720 is also serpentine to some extent to increase its inductance, which is not the case in unit cell 320. Unit cell 720 will have the same equivalent circuit as unit cell 320 and, if appropriate design techniques are applied, can have the same capacitance and inductance values ​​as those present in unit cell 320. Therefore, Figures 5A-5C This is simply illustrated as how the unit cell 320 (or other unit cells disclosed herein) can be efficiently replicated using a printed circuit board including multiple metallization layers.

[0096] It will be appreciated that many modifications may be made to the frequency selective surface described above without departing from the present invention. As an example, the metal pads and / or openings may have shapes different than those shown above. The serpentine edge capacitor may have a different design, and the metal traces may be serpentine to increase their inductance.

[0097] Frequency selective surfaces according to embodiments of the present invention may be used in many applications, including in passive / active antenna systems in which the frequency selective surface may act as a reflector for low-band and / or mid-band linear arrays mounted in front of the frequency selective surface and may be substantially transparent to RF radiation in the operating band of a high-band beamforming array mounted behind the frequency selective surface.

[0098] The present invention has been described above with reference to the accompanying drawings. The present invention is not limited to the illustrated embodiments. Rather, these embodiments are intended to fully and completely disclose the present invention to those skilled in the art. In the accompanying drawings, like reference numerals represent like elements throughout. For clarity, the thickness and dimensions of some components may be exaggerated.

[0099] For ease of description, spatially relative terms such as "below," "beneath," "lower," "above," "upper," "top," "bottom," etc. may be used herein to describe the relationship of one element or feature to another element or features as shown in the accompanying drawings. It should be understood that in addition to the orientations shown in the figures, spatially relative terms are intended to cover different orientations of the device in use or operation. For example, if the device in the figure is turned over, elements described as "below" or "below" other elements or features will be oriented as "above" the other elements or features. Thus, the exemplary term "below" can cover both the orientations of above and below. The device can be oriented in other ways (rotated 90 degrees or other orientations), and the spatially relative descriptors used herein are interpreted accordingly.

[0100] Herein, unless stated otherwise, the terms "attached," "connected," "interconnected," "contacting," "mounted," "coupled," and the like may mean a direct or indirect attachment or coupling between elements.

[0101] For brevity and / or clarity, well-known functions or constructions may not be described in detail.As used herein, the expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0102] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are also intended to include the plural forms. It will be further understood that when used in this specification, the terms "comprises / comprising," "includes and / or including" specify the presence of the features, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, operations, elements, components, and / or groups thereof.

Claims

1. A base station antenna, comprising: arrays of lower frequency band radiating elements; arrays of higher frequency band radiating elements; as well as A frequency selective surface having a plurality of unit cells, wherein an equivalent circuit of each unit cell includes a first parallel inductor-capacitor ("LC") circuit embedded within a second parallel LC circuit.

2. The base station antenna according to claim 1, wherein the first parallel LC circuit is connected in series with a capacitor of the second parallel LC circuit. 3 . The base station antenna of claim 1 , wherein a ratio of a first inductance of the first parallel LC circuit to a second inductance of the second parallel LC circuit is between 0.5 and 2.

0.

4. The base station antenna of claim 3, wherein a ratio of a first capacitance of the first parallel LC circuit to a second capacitance of the second parallel LC circuit is between 0.5 and 2.

0.

5. The base station antenna of claim 1, wherein the array of lower frequency band radiating elements is mounted in front of the frequency selective surface and the array of higher frequency band radiating elements is mounted behind the frequency selective surface. 6 . The base station antenna of claim 1 , wherein a first unit cell of the unit cells comprises a plurality of metal pads and a plurality of metal traces connecting each of the plurality of metal pads to all other metal pads of the plurality of metal pads. 7 . The base station antenna according to claim 6 , wherein each metal pad of the plurality of metal pads is separated from at least one other metal pad of the plurality of metal pads by a serpentine gap. The base station antenna according to claim 7 , wherein each serpentine gap has a periodic waveform shape. 9 . The base station antenna according to claim 6 , wherein a metal pad of a first unit cell among the unit cells is separated from an adjacent unit cell by a gap. 10 . The base station antenna of claim 9 , wherein a first one of the unit cells further comprises an outer metal ring surrounding the gap. 11 . The base station antenna of claim 10 , wherein the outer metal ring comprises a plurality of sides, and wherein each side of the outer metal ring is integral with a side of the outer metal ring of a corresponding unit cell adjacent to a first unit cell among the unit cells.

12. The base station antenna of claim 1 , wherein a first unit cell among the unit cells comprises a plurality of metal pads surrounded by a continuous gap extending around a perimeter of the metal pads, and wherein each metal pad is separated from at least one other of the metal pads by a serpentine gap.

13. The base station antenna of claim 12, wherein the frequency selective surface is implemented in a printed circuit board comprising a dielectric substrate and a metallization pattern on a first side of the dielectric substrate, and wherein the metal pad is part of the metallization pattern. 14 . The base station antenna according to claim 13 , wherein a plurality of openings are provided in the metallization pattern, wherein the plurality of metal pads surround the openings.

15. The base station antenna of claim 14, wherein the serpentine gap extends from a first one of the openings to the continuous gap.

16. The base station antenna of claim 15, wherein the openings define a plurality of metal traces that are part of a metallization pattern connecting each metal pad to the rest of the metal pads.

17. The base station antenna of claim 16, wherein when the base station antenna is installed for use, at least one of the metal traces extends at a 45° angle, and another of the metal traces extends at a -45° angle.

18. The base station antenna of claim 1, wherein a first unit cell among the unit cells comprises a first metal pad and a second metal pad adjacent to each other, wherein the first metal pad has a first edge comprising a plurality of spaced-apart first metal protrusions, and the second metal pad has a second edge comprising a plurality of spaced-apart second metal protrusions. The base station antenna according to claim 18 , wherein the second metal protrusion and the first metal protrusion intersect with each other.

20. A base station antenna, comprising: arrays of lower frequency band radiating elements; arrays of higher frequency band radiating elements; as well as A frequency selective surface having a plurality of unit cells, wherein each unit cell includes a plurality of metal pads, wherein each metal pad is capacitively coupled to two other metal pads among the metal pads and is galvanically coupled to at least another metal pad among the metal pads via one or more metal traces among a plurality of metal traces.

21. The base station antenna of claim 20, wherein each metal pad of a first one of the unit cells is capacitively coupled to two other metal pads of the first one of the unit cells through a pair of serpentine edge capacitors.

22. The base station antenna of claim 20, wherein the frequency selective surface is implemented in a printed circuit board including a dielectric substrate, and each metal pad in a first one of the unit cells is capacitively coupled to two other metal pads of the first one of the unit cells through the dielectric substrate.

23. The base station antenna of claim 20, wherein each unit cell further comprises an outer metal ring surrounding the plurality of metal pads.

24. The base station antenna of claim 23, wherein the outer metal ring of each unit cell is integral with the outer ring of an adjacent unit cell.

25. The base station antenna of claim 20, wherein a first metal pad among the metal pads comprises a first edge including a plurality of spaced-apart first metal protrusions, and a second metal pad adjacent to the first metal pad among the metal pads comprises a plurality of spaced-apart second metal protrusions. The base station antenna according to claim 25 , wherein the second metal protrusion and the first metal protrusion intersect with each other.

27. The base station antenna of claim 20, wherein the frequency selective surface is implemented in a printed circuit board, the printed circuit board comprising a dielectric substrate and a metallization pattern comprising the plurality of metal pads, wherein a plurality of openings are provided at the center of each unit cell, and the plurality of metal pads of each unit cell surround the plurality of openings of the unit cell.

28. The base station antenna of claim 27, wherein the opening of each unit cell defines a plurality of metal traces per unit cell.

29. The base station antenna of claim 20, wherein the equivalent circuit of each unit cell comprises a first parallel inductor-capacitor ("LC") circuit embedded within a second parallel LC circuit.

30. The base station antenna of claim 29, wherein the first parallel LC circuit is connected in series with a capacitor of the second parallel LC circuit.

31. A base station antenna, comprising: arrays of lower frequency band radiating elements; arrays of higher frequency band radiating elements; as well as A frequency selective surface having a plurality of unit cells, wherein a first unit cell among the unit cells comprises a plurality of metal pads, wherein each metal pad is capacitively edge-coupled to another metal pad among the metal pads through a corresponding serpentine gap among a plurality of serpentine gaps.

32. The base station antenna of claim 31, wherein each serpentine gap has a periodic waveform shape. 33 . The base station antenna of claim 32 , wherein a first unit cell among the unit cells further comprises an outer metal ring surrounding the metal pad, the outer metal ring being separated from the metal pad by a gap providing no metal.

34. The base station antenna of claim 32, wherein each of the unit cells comprises a plurality of metal pads and an outer metal ring surrounding the metal pads, and wherein the outer metal ring of each unit cell directly contacts the outer metal ring of each adjacent unit cell.

35. The base station antenna of claim 31, wherein the frequency selective surface is implemented in a printed circuit board comprising a dielectric substrate and a metallization pattern on a first side of the dielectric substrate.

36. The base station antenna of claim 35, wherein the serpentine gap comprises a gap in the metallization pattern that exposes the dielectric substrate.

37. The base station antenna of claim 36, wherein the metallization pattern comprises a plurality of openings in the center of each unit cell, wherein the openings in the metallization pattern in each unit cell are surrounded by a plurality of metal pads of each respective unit cell.

38. The base station antenna of claim 37, wherein a first unit cell among the unit cells further comprises an outer metal ring separated from the metal pad of the first unit cell among the unit cells by a continuous gap, and wherein one of the plurality of serpentine gaps extends from a first opening in the metallization pattern of the first unit cell among the unit cells to the continuous gap.

39. The base station antenna of claim 31 , wherein the equivalent circuit of each unit cell comprises a first parallel inductor-capacitor ("LC") circuit embedded within a second parallel LC circuit.

40. The base station antenna of claim 39, wherein the first parallel LC circuit is connected in series with a capacitor of the second parallel LC circuit.

41. The base station antenna of claim 31 , wherein the array of lower frequency band radiating elements is mounted in front of the frequency selective surface and the array of higher frequency band radiating elements is mounted behind the frequency selective surface.

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