Modular base station antenna systems having a passive base station antenna and a passive mid-band antenna module

Abstract

An antenna system comprises a passive base station antenna that includes first and second arrays of low-band radiating elements that are configured to operate in at least a portion of a 617-960 MHz frequency band and a passive antenna module that is mounted behind the passive base station antenna and configured to transmit and receive RF signals through the passive base station antenna.

Description

Attorney Docket No.9833.7264.WO MODULAR BASE STATION ANTENNA SYSTEMS HAVING A PASSIVE BASE STATION ANTENNA AND A PASSIVE MID-BAND ANTENNA MODULE CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to U.S. Provisional Patent Application Serial No.63 / 536,973, filed September 7, 2023, the entire content of which is incorporated herein by reference. FIELD

[0002] The present invention relates to communications systems and, in particular, to base station antennas for cellular communications systems. BACKGROUND

[0003] Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as "cells" which are served by respective base stations. Each base station may include one or more base station antennas that are configured to provide two-way radio frequency ("RF") communications with mobile subscribers that are within the cell served by the base station. Typically, the base station antennas are mounted on a tower or other raised structure, with the radiation patterns (also referred to herein as "antenna beams") that are generated by the base station antennas directed outwardly.

[0004] A common base station configuration is the three sector configuration in which a cell is divided into three 120º "sectors" in the azimuth (horizontal) plane. A separate base station antenna provides coverage (service) to 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 typically referred to as "linear arrays," and may be straight columns of radiating elements orAttorney Docket No.9833.7264.WO columns in which some of the radiating elements are staggered horizontally to narrow the beamwidths of the generated antenna beams in the azimuth plane. Most modern base station antennas include both "low-band" linear arrays of radiating elements that support service in some or all of the 617-960 MHz frequency band and "mid-band" linear arrays of radiating elements that support service in some or all of the 1427-2690 MHz frequency band. These linear arrays are typically formed using dual-polarized radiating elements, which allows each array to transmit and receive RF signals at two orthogonal polarizations.

[0005] Each of the above-described linear arrays of dual-polarized radiating elements is coupled to two ports of a radio (one port for each polarization). An RF signal that is to be transmitted by a linear array is passed from the radio to the antenna where it is divided into a plurality of sub-components, with each sub-component fed to a respective subset of the radiating elements in the linear array (typically each sub-component is fed to between one and three radiating elements). The sub-components of the RF signal are transmitted through the radiating elements to generate an antenna beam that covers a generally fixed coverage area, such as a sector of a cell. Typically these linear arrays will have remote electronic tilt ("RET") capabilities which allow a cellular operator to change the pointing angle of the generated antenna beams in the elevation (vertical) plane in order to change the size of the sector served by the linear array. Since the antenna beams generated by the above-described 2G / 3G / 4G linear arrays generate static antenna beams that only change in shape due to adjustments in the downtilt angle of the antenna beam, they are often referred to as "passive" linear arrays.

[0006] Most cellular operators are currently upgrading their networks to support fifth generation ("5G") cellular service. One important component of 5G cellular service is the use of so-called multi-column "active" beamforming arrays that operate in conjunction with beamforming radios to dynamically adjust the size, shape and pointing direction of the antenna beams that are generated by the active beamforming array. 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 and / or the 5.1-5.8 GHz frequency bands. The radiating elements in each column of such an active beamforming array are typically coupled to a respective port of a beamforming radio. The beamforming radio may be a separate device, or may be integrated with the active antenna array. The beamforming radio may adjust theAttorney Docket No.9833.7264.WO amplitudes and phases of the sub-components of an RF signal that are fed to each port of the radio (and hence to each respective column of radiating elements in the multi-column beamforming array) in order to generate antenna beams that have narrowed beamwidths in the azimuth plane and / or elevation plane (and hence higher antenna gain). These narrowed antenna beams can be electronically steered by proper selection of the amplitudes and phases of the sub- components of an RF signal.

[0007] In order to avoid having to increase the number of antennas at cell sites, the above-described 5G antennas also often include passive linear arrays that support legacy 2G, 3G and / or 4G cellular services. In some cases, both the active beamforming arrays and the passive linear arrays may be included in a single base station antenna. Another solution for providing an antenna that supports both 2G / 3G / 4G and 5G cellular service is to mount a 5G active antenna module (i.e., a module that includes an active beamforming array and associated beamforming radio) behind a passive base station antenna that includes a plurality of 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 beams generated by the 5G active beamforming array can be transmitted through the passive base station antenna. This design is advantageous as the active antenna module may be removable, and hence as enhanced 5G capabilities are developed, a cellular operator may initially only deploy the passive base station antenna and add the active antenna modules later, or may replace an originally-deployed active antenna module with an upgraded active antenna module without having to replace the passive base station antenna. Herein, the combination of a passive base station antenna that has an active antenna module mounted behind it is referred to as a "passive / active antenna system." SUMMARY

[0008] Pursuant to embodiments of the present invention, antenna systems are provided that comprise a passive base station antenna that includes first and second arrays of first frequency band radiating elements and a first frequency selective surface that is reflective in the first frequency band and transmissive in a second frequency band and a first antenna module that is mountable behind the first frequency selective surface, the first antenna module comprising at least first and second arrays of second frequency band radiating elements In these antenna systems, the first and second arrays of second frequency band radiating elements are configured to generate static antenna beams that provide coverage to a predefined sector.Attorney Docket No.9833.7264.WO

[0009] In some embodiments, the first antenna module may further comprise third and fourth arrays of second frequency band radiating elements that are configured to generate static antenna beams that provide coverage to the predefined sector. In such embodiments, the first through fourth arrays of second frequency band radiating elements may be configured to transmit and receive RF signals through the first frequency selective surface.

[0010] In some embodiments, the first antenna module may further comprise a first remote electronic tilt ("RET") actuator that is operatively coupled to first and second phase shifters that are associated with the first array of second frequency band radiating elements and a second RET actuator that is operatively coupled to third and fourth phase shifters that are associated with the third array of second frequency band radiating elements.

[0011] In some embodiments, the first antenna module may not include a calibration circuit.

[0012] In some embodiments, the passive base station antenna may further comprise a second frequency selective surface that is reflective in the first frequency band and transmissive in a third frequency band. In some embodiments, the third frequency band may encompass frequencies that are higher than the frequencies in the first and second frequency bands, and the second frequency band may encompass frequencies that are higher than the frequencies in the first frequency band. In some embodiments, the second frequency selective surface may also be reflective in the second frequency band. In some embodiments, the antenna system may further comprise a second antenna module that is mounted behind the second frequency selective surface, the second antenna module including a multicolumn beamforming array.

[0013] In some embodiments, the passive base station antenna may further comprise a reflector assembly that has a first opening, and the first frequency selective surface extends over the first opening

[0014] Pursuant to further embodiments of the present invention, antenna systems are provided that comprise a passive base station antenna that includes first and second arrays of low-band radiating elements that are configured to operate in at least a portion of a 617-960 MHz frequency band and a first antenna module that is mountable behind the passive base station antenna and configured to generate antenna beams that pass through the passive base station antenna. These antenna system further include a first array of mid-band radiating elements that are configured to operate in at least a portion of a 1427-2690 MHz frequency band, where a firstAttorney Docket No.9833.7264.WO sub-set of the mid-band radiating elements in the first array are part of the passive base station antenna and a second sub-set of the radiating elements in the first array are part of the first antenna module.

[0015] In some embodiments, the antenna system may further comprise second through fourth arrays of mid-band radiating elements that are each configured to operate in at least a portion of the 1427-2690 MHz frequency band, where first sub-sets of the mid-band radiating elements in each of the second through fourth arrays are part of the passive base station antenna and second sub-sets of the radiating elements in the second through fourth arrays are part of the first antenna module.

[0016] In some embodiments, the passive base station antenna may further comprise a first frequency selective surface that is configured to reflect RF energy in at least a portion of the 617-960 MHz frequency band and to pass RF energy in at least a portion of the 1427-2690 MHz frequency band, and the first antenna module is mounted behind the first frequency selective surface.

[0017] In some embodiments, the passive base station antenna may further comprise a reflector assembly that has a main reflector and first and second reflector strips that define a first opening, and the first frequency selective surface extends over the first opening.

[0018] In some embodiments, the first sub-set of the mid-band radiating elements in the first array may be mounted to extend forwardly from the main reflector.

[0019] In some embodiments, the first antenna module may include a phase shifter, and an output of the phase shifter may be coupled to the second sub-set of the mid-band radiating elements in the first array.

[0020] Pursuant to still further embodiments of the present invention, antenna systems are provided that comprise a passive base station antenna that includes first and second arrays of low-band radiating elements that are configured to operate in at least a portion of a 617-960 MHz frequency band and a passive antenna module that is mounted behind the passive base station antenna and configured to transmit and receive RF signals through the passive base station antenna.

[0021] In some embodiments, the first antenna module may comprise first through fourth arrays of mid-band radiating elements that are configured to operate in at least a portion of a 1427-2690 MHz frequency band.Attorney Docket No.9833.7264.WO

[0022] In some embodiments, each of the first through fourth arrays of mid-band radiating elements may be configured to generate static antenna beams that provide coverage to a 120⁰ sector in an azimuth plane of the antenna system.

[0023] In some embodiments, the passive base station antenna may include a first frequency selective surface that is configured to reflect RF energy in at least a portion of the 617- 960 MHz frequency band and to pass RF energy in at least a portion of the 1427-2690 MHz frequency band.

[0024] In some embodiments, the passive base station antenna may further comprise a second frequency selective surface that is reflective in at least a portion of the 617-960 MHz frequency band and transmissive in at least a portion of the 3.1-4.2 GHz frequency band.

[0025] In some embodiments, the passive antenna module may not include a calibration circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG.1A is a schematic rear perspective view of a conventional passive / active antenna system that comprises a passive base station antenna and an associated active antenna module.

[0027] FIG.1B is a schematic perspective view of the conventional passive / active antenna system of FIG.1A with the radome of the passive base station antenna and the radome and a frequency selective surface of the active antenna module omitted.

[0028] FIG.2A is a schematic perspective view of another conventional passive / active antenna system that comprises a passive base station antenna and two associated active antenna modules.

[0029] FIG.2B is a schematic plan view of the passive base station antenna of the conventional passive / active antenna system of FIG.2A with a radome thereof removed.

[0030] FIG.3A is a schematic perspective view of a modular passive / active antenna system according to embodiments of the present invention.

[0031] FIG.3B is a schematic plan view of the passive base station antenna included in the passive / active antenna system of FIG.3A.

[0032] FIG.3C is a schematic plan view of a first antenna module that may be mounted behind the passive base station antenna of FIG.3A.Attorney Docket No.9833.7264.WO

[0033] FIG.3D is a schematic plan view of a second antenna module that may be mounted behind the passive base station antenna of FIG.3A.

[0034] FIG.3E is a schematic plan view of a third antenna module that may be mounted behind the passive base station antenna of FIG.3A.

[0035] FIG.3F is a schematic plan view of a fourth antenna module that may be mounted behind the passive base station antenna of FIG.3A instead of the third antenna module of FIG.3E.

[0036] FIG.4 is a schematic plan view of a passive base station antenna that is part of a modular passive / active antenna system according to further embodiments of the present invention.

[0037] FIG.5A is a schematic side view of a modular passive / active antenna system according to still further embodiments of the present invention.

[0038] FIG.5B is a schematic plan view of the passive base station antenna of the modular passive / active antenna system of FIG.5A with the radome thereof removed.

[0039] FIG.5C is a schematic plan view of a passive antenna module that may be mounted behind the passive base station antenna of FIG.5B.

[0040] The passive base station antennas according to embodiments of the present invention include frequency selective surfaces. In many of the drawings, some or all of these frequency selective surfaces are shown schematically using dashed boxes in order to simplify the drawings. These dashed boxes show the position of the frequency selective surfaces, but not the specific design thereof. Some of the drawings show actual implementations of frequency selective surfaces. The frequency selective surfaces that are shown schematically may have the same or similar designs as the ones shown in the figures. DETAILED DESCRIPTION

[0041] FIGS.1A-1B illustrate a conventional passive / active antenna system 100 that includes both a passive base station antenna 110 and an active antenna module 150. In particular, FIG.1A is a schematic rear perspective view of the passive / active antenna system 100. FIG.1B is a schematic perspective view of the passive / active antenna system 100 of FIG. 1A with a radome of the passive base station antenna 110 and a radome and frequency selective surface of the active antenna module 150 omitted. In FIGS.1A and 1B, the axes illustrate the vertical (V), horizontal (H) and forward (F) directions of the base station antenna system 100.Attorney Docket No.9833.7264.WO

[0042] Referring to FIG.1A, the passive / active antenna system 100 may be mounted, for example, on an antenna tower 102 using mounting hardware 104. The passive / active antenna system 100 includes the passive base station antenna 110 and the active antenna module 150. The active antenna module 150 is mounted behind the passive base station antenna 110. The active antenna module 150 may be mounted directly on a rear surface of the passive base station antenna 110, or may be held in place behind the passive base station antenna 110 by, for example, the mounting hardware 104 that is used to mount the passive / active antenna system 100 on the antenna tower 102 (or other structure). The front surface of the passive / active antenna system 100 may be opposite the antenna tower 102 facing toward a coverage area of the passive / active antenna system 100. The passive base station antenna 110 includes a tubular radome 112 that surrounds and protects an antenna assembly that is mounted inside the radome 112. A top end cap 114 covers a top opening in the radome 112 and a bottom end cap 116 covers a 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 radios (not shown). The active antenna module 150 may be removably mounted behind the passive base station antenna 110 so that the active antenna module 150 may later be 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 that 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 configured to transmit and receive RF signals through the passive base station antenna 110.

[0043] Referring to FIG.1B, the passive base station antenna 110 includes a reflector assembly 120 and a plurality of passive linear arrays of radiating elements that extend forwardly from the passive reflector assembly 120. The linear arrays may support, for example, 3G and / or 4G cellular service. In the example passive base station antenna 110 shown in FIGS.1A-1B, the linear arrays include first and second low-band linear arrays 130-1, 130-2 that are configured to operate in all or part of the 617-960 MHz frequency band. Each low-band linear array 130 comprises a vertically-extending column of low-band radiating elements 132. The passive base station antenna 110 further includes first through fourth mid-band linear arrays 140-1 through 140-4 that are configured to operate in all or part of the 1427-2690 MHz frequency band. Each mid-band linear array 140 comprises a vertically-extending column of mid-band radiatingAttorney Docket No.9833.7264.WO elements 142. Each of the low-band and mid-band linear arrays 130, 140 are passive linear arrays that generate static antenna beams that provide coverage to a predefined coverage area (e.g., antenna beams that are each configured to cover a sector of a base station), with the only change to the coverage area occurring when the electronic downtilt angles of the generated antenna beams are adjusted (e.g., to change the size of the cell).

[0044] Each of the low-band and mid-band radiating elements 132, 142 may be implemented as dual-polarized radiating elements that include first and second radiators that transmit and receive RF energy at orthogonal polarizations. When such dual-polarized radiating elements are used, each of the low-band and mid-band linear arrays 130, 140 may be connected to a pair of the RF ports 118. The first RF port 118 is connected between a first port of a radio (e.g., a remote radio head mounted on the antenna tower 102 near the passive base station antenna 110) and the first polarization radiators of the radiating elements in the linear array, and the second RF port 118 is connected between a second port of a radio and the second polarization radiators of the radiating elements in the linear array. RF signals that are to be transmitted by a selected one of the linear arrays 130, 140 are passed from the radio to one of the RF ports 118, and passed from the RF port 118 to a power divider (or, alternatively, a phase shifter assembly that includes a power divider) that divides the RF signal into a plurality of sub- components that are fed to the respective first or second radiators of the radiating elements in the linear array so that the sub-components are radiated into free space.

[0045] The passive reflector assembly 120 includes a main reflector 122 and spaced- apart first and second reflector strips 124-1, 124-2 that extend vertically from respective first and second opposed sides of the main reflector 122. The passive reflector assembly 120 may further include a third reflector strip 124-3 that extends in the horizontal direction between the first and second reflector strips 124-1, 124-2. An opening 126 is defined between the first and second reflector strips 124-1, 124-2. For example, the opening 126 may be bounded by a top portion of the main reflector 122, the first and second reflector strips 124-1, 124-2, and the third reflector strip 124-3. Most of the low-band and mid-band radiating elements 132, 142 are mounted to extend forwardly from the main reflector 122. However, low-band linear arrays 130-1, 130-2 and mid-band linear arrays 140-1, 140-4 each extend substantially the full length of the passive / active antenna system 100 and hence 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-Attorney Docket No.9833.7264.WO band radiating elements 132, 142 that are positioned above the main reflector 122. The first and second reflector strips 124-1, 124-2 may be integral with the main reflector 122 so that the first and second reflector strips 124-1, 124-2 and the main reflector 122 will be maintained at a common ground voltage, which may be important for the performance of the linear arrays 130-1, 130-2, 140-1, 140-4.

[0046] Each low-band radiating element 132 may comprise a slant -45⁰ / +45⁰ cross-dipole radiating element that includes a -45⁰ dipole radiator 134-1 and a +45⁰ dipole radiator 134-2 that are arranged to form a cross when the radiating element 132 is viewed from the front. The dipole radiators 134 may (but need not) extend in a plane that is parallel to a plane defined by the main reflector 122. Each mid-band radiating element 142 may likewise comprise a slant - 45⁰ / +45⁰ cross-dipole radiating element that includes a -45⁰ dipole radiator and a +45⁰ dipole radiator.

[0047] The dipole radiators 134-1, 134-2 may be mounted on a feed stalk (not visible in the figures) of the radiating element 132 that passes RF signals between the dipole radiators and an associated feed network. Conventionally, cross-dipole radiating elements extend forwardly from a main reflector surface of a reflector assembly with the feed stalks of the radiating elements extending perpendicularly to the main reflector surface. The radiating elements 132 that extend forwardly from the main reflector 122 may have a conventional design where the feed stalks extend perpendicularly to the main reflector 122. However, the centers of the low- band radiating elements 132 that are mounted on the first and second reflector strips 124-1, 124- 2 are above the opening 126, and hence conventional radiating elements cannot be readily used. Thus, the three uppermost low-band radiating elements 132 have so-called "tilted" feed stalks 136 that extend forwardly from the reflector strips 124-1, 124-2 at oblique angles. In particular, the base of each feed stalk is mounted on one of the reflector strips 124-1, 124-2, and the feed stalk extends at an angle so that the center of the cross defined by the dipole radiators 134-1, 134-2 is above the opening 126.

[0048] The active antenna module 150 includes a multi-column beamforming array 160 of radiating elements 162 and a beamforming radio (not visible in the figures). The multi- column beamforming array 160 may be mounted behind a front radome of the active antenna module 150 (the radome of the active antenna module 150 is omitted in FIG.1B to show the beamforming array 160), and the beamforming radio may be mounted behind the multi-columnAttorney Docket No.9833.7264.WO beamforming array 160. The beamforming array 160 may, for example, comprise a plurality of vertically-extending columns of high-band radiating elements 162 that are configured to operate in all or part of the 3.1-4.2 GHz frequency band. The high-band radiating elements 162 are mounted to extend forwardly from a reflector 154 of the active antenna module 150. The beamforming radio is capable of electronically adjusting the amplitudes and / or phases of the subcomponents of an RF signal that are output to different radiating elements 162 of the multi- column beamforming array 160. For example, each port of the beamforming radio may be coupled to a column of radiators of the beamforming array 160, and the amplitudes and phases of the sub-components of the RF signal that are fed to the radiators in each column may be adjusted so that the generated antenna beam is narrowed in the azimuth plane and pointed in a desired direction in the azimuth plane.

[0049] As is shown in FIG.1B, the beamforming array 160 of active antenna module 150 is mounted behind the opening 126 in the passive reflector assembly 120. The beamforming array 160 is visible in FIG.1B as the radomes of both the passive base station antenna 110 and the active antenna module 150 are removed in the view of FIG.1B. The opening 126 in the passive reflector assembly 120 allows the antenna beams generated by the beamforming array 160 to pass through the passive base station antenna 110 and out of 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.

[0050] In some embodiments, the opening 126 in the passive reflector assembly 120 may be covered by a frequency selective surface 128. The frequency selective surface 128 may act as a spatial filter that passes, or substantially attenuates and / or reflects RF energy, depending on the frequency of the RF energy. Frequency selective surfaces are known in the art, and typically comprise a grid pattern of unit cells such as a grid pattern of metal patches and / or other metal structures that form resonant circuits. The metal patches / structures may be arranged in one or more layers. The frequency selective surface 128 may be implemented, for example, as a piece of sheet metal with the grid structure punched or otherwise formed therein or as a dielectric substrate with one or more metal patterns formed therein (such as a printed circuit board). The frequency selective surface 128 may be configured to substantially pass RF energy that is incident thereon in a first frequency range (here the first frequency range may include the operating frequency band of the radiating elements included in the multi-column array 160 ofAttorney Docket No.9833.7264.WO high-band radiating elements 162 in active antenna module 150), while partially or substantially not passing (e.g., reflecting) RF energy that is incident thereon in a second frequency range (here the second frequency range may include the operating frequency bands of the radiating elements included in the passive base station antenna 110). Examples of frequency selective surfaces are discussed in U.S. Patent No.11,482,774 to Hou et al., the entire content of which is incorporated herein by reference.

[0051] FIG.2A is a schematic rear perspective view of another conventional passive / active antenna system 200 that includes both a passive base station antenna 210 and a pair of active antenna modules 250-1, 250-2. FIG.2B is a schematic plan view of the passive base station antenna 210 with a radome thereof removed. The passive / active antenna system 200 of FIGS.2A-2B is similar to the passive / active antenna system 200 that is described above, so the description below will focus on the differences between the two passive / active antenna systems 100, 200.

[0052] The passive base station antenna 210 includes a reflector assembly 220 that is similar to the reflector assembly 120, but includes a smaller main reflector 222 that is positioned in the middle portion (longitudinally) of the base station antenna 210.

[0053] Spaced-apart first and second reflector strips 224-1, 224-2 extend vertically from respective first and second opposed upper sides of the main reflector 222 and a third reflector strip 224-3 extends in the horizontal direction between the first and second reflector strips 224-1, 224-2. Additionally, fourth and fifth reflector strips 224-4, 224-5 extend vertically from respective first and second opposed lower sides of the main reflector 222, and a sixth reflector strip 224-6 extends in the horizontal direction between the fourth and fifth reflector strips 224-4, 224-5. The first, second, fourth and fifth reflector strips 224-1, 224-2, 224-4, 224-5 may be integral with the main reflector 222. A first opening 226-1 is defined between the first and second reflector strips 224-1, 224-2, and a second opening 226-2 is defined between the fourth and fifth reflector strips 224-4, 224-5. Frequency selective surfaces 228-1, 228-2 cover the respective openings 226-1, 226-2. The frequency selective surfaces 228-1, 228-2 are shown schematically as dashed boxes in FIG.2B to simplify the figure. The frequency selective surfaces 228-1, 228-2 may be configured to reflect RF energy in the 617-960 MHz and the 1427- 2690 MHz frequency bands (or selected sub-bands thereof) while passing RF energy in the 3.1- 4.2 GHz frequency band (or selected sub-bands thereof).Attorney Docket No.9833.7264.WO

[0054] The passive base station antenna 210 includes first and second low-band linear arrays 230-1, 230-2 of low-band radiating elements 232 that that are configured to operate in all or part of the 617-960 MHz frequency band. The low-band radiating elements 232 of the first low-band linear array 230-1 are mounted on the first reflector strip 224-1, the main reflector 222 and the fourth reflector strip 224-4. The low-band radiating elements 232 of the second low- band linear array 230-2 are mounted on the second reflector strip 224-2, the main reflector 222 and the fifth reflector strip 224-5. The low-band linear arrays 230-1, 230-2 may generate static antenna beams that provide coverage to a predefined coverage area. Some or all of the low-band radiating elements 232 may be identical to the low-band radiating elements 132 that are described above.

[0055] The passive base station antenna 210 also includes first and second mid-band linear arrays 240-1, 240-2 of mid-band radiating elements 242 that are configured to operate in all or part of the 1427-2690 MHz frequency band. The mid-band radiating elements 242 of the first mid-band linear array 230-1 are mounted on the first reflector strip 224-1, the main reflector 222 and the fourth reflector strip 224-4. The mid-band radiating elements 242 of the second mid-band linear array 230-2 are mounted on the second reflector strip 224-2, the main reflector 222 and the fifth reflector strip 224-5. The mid-band linear arrays 240-1, 240-2 may generate static antenna beams that provide coverage to a predefined coverage area and the mid-band radiating elements 242 may be identical to the mid-band radiating elements 142 that are described above. Unlike passive base station antenna 110, passive base station antenna 210 does not include third and fourth mid-band linear arrays.

[0056] The first and second active antenna modules 250-1, 250-2 each includes a respective multi-column beamforming array of high-band radiating elements and a beamforming radio. Each active antenna module 250-1, 250-2 may be identical to the active antenna module 150 described above, so further description of active antenna modules 250-1, 250-2 will be omitted. Two active antenna modules 250-1, 250-2 may be mounted behind passive base station antenna 210 since passive base station antenna 210 includes two openings 226-1, 226-2 that are covered by the respective frequency selective surfaces 228-1, 228-2, thereby allowing the two beamforming arrays to transmit and receive RF signals through the passive base station antenna 210.Attorney Docket No.9833.7264.WO

[0057] Cellular operators are now deploying base station antennas having multicolumn beamforming arrays that operate in the upper portion of the mid-band frequency range (i.e., mid- band beamforming arrays). For example, there is demand for base station antennas that include multicolumn beamforming arrays that operate in the 2.5-2.7 GHz frequency band. It may be challenging, however, to provide a passive / active antenna system that includes an active antenna module that has a multicolumn beamforming array that operates in the mid-band frequency range for at least two reasons. First, since a mid-band beamforming array has larger radiating elements that are spaced farther apart than a comparable high-band beamforming array, the lateral width of the beamforming array is increased. As a result, the widths of the reflector strips in the passive base station antenna may need to be reduced (in order to keep the overall width of the passive base station antenna within acceptable limits), and hence there may not be room for both low-band and mid-band radiating elements on the reflector strips that surround a 2.5-2.7 GHz beamforming array. Second, since the frequency selective surface that is positioned in front of the 2.5-2.7 GHz beamforming array is designed to pass 2.5-2.7 GHz RF signals, the mid-band radiating elements in the passive base station antenna should not extend onto the reflector strips that are positioned on either side of the 2.5-2.7 GHz beamforming array. Since the 2.5-2.7 GHz beamforming array will be the longer of the two beamforming arrays (since the radiating elements thereof are larger and spaced farther apart as compared to the radiating elements of, for example, a 3.5-3.7 GHz beamforming array), the mid-band radiating elements included in the passive base station antenna may need to be shortened significantly and thus may exhibit inadequate gain.

[0058] Pursuant to embodiments of the present invention, passive / active antenna systems are provided that are modular in nature. These passive / active antenna systems may include a passive base station antenna, afirst antenna module that includes a high-band beamforming array, along with either (1) a second antenna module that includes a plurality of passive mid-band linear arrays or (2) a third antenna module that includes a high-band beamforming array. The present invention is based, in part, on the realization that when a passive / active antenna system includes a mid-band beamforming array, in many instances the cellular operator will not also require (or not require as many) traditional passive mid-band linear arrays that generate static antenna beams. As such, instead of including mid-band linear arrays in the passive base station antenna of the passive / active antenna system, the mid-band linear arrays may (at least in part) beAttorney Docket No.9833.7264.WO included in a separate antenna module that is mounted on the rear side of the passive base station antenna 210. This arrangement has several potential advantages.

[0059] First, it allows for a passive / active antenna system that initially includes a passive base station antenna having two passive low-band linear arrays and (optionally) two passive mid- band linear arrays, a first antenna module that includes an additional four passive mid-band linear arrays, and a second antenna module that includes a high-band beamforming array. The passive / active antenna system may later be upgraded to replace the first antenna module (which includes four passive mid-band linear arrays) with a third antenna module that includes a multi- column mid-band beamforming array. As discussed above, it may be challenging to achieve this functionality in conventional passive / active antenna systems because, to have sufficient gain, the passive mid-band linear arrays would need to extend in front of the mid-band beamforming array. This causes difficulties because the mid-band arrays in the passive base station antenna may need an underlying frequency selective surface that reflects mid-band RF energy, while the mid-band beamforming array in the antenna module may need a frequency selective surface that is transparent to mid-band RF energy.

[0060] Second, the conventional passive / active antenna systems 100, 200 employ frequency selective surfaces that are substantially reflective across the 617-960 MHz and 1427- 2690 MHz frequency bands while being transmissive across, for example, the 3.1-4.2 GHz frequency band or a portion thereof (e.g., the 3.5-3.7 GHz frequency band). It can be challenging, however, to provide frequency selective surfaces that given the relatively small gap (in terms of percentage) between 2690 MHz and 3.1 GHz or even between 2690 MHz and 3.5 GHz. As a result, the frequency selective surface may reflect a relatively larger percentage of the higher band energy and / or pass relatively larger percentage of the lower band RF energy, both of which are undesirable. Increased reflection at the higher frequency band can reduce the gain of the beamforming array, among other disadvantages. Reduced reflectivity in the lower frequency bands can reduce the gain of the lower frequency arrays, and can also increase the possibility of PIM distortion generation.

[0061] The passive / active systems according to embodiments of the present invention may use, for example, frequency selective surfaces that are substantially reflective across the 617-960 MHz frequency band while being transmissive across, for example, the 1427-2690 MHz (or 1695-2690 MHz) and / or 3.1-4.2 GHz frequency bands or selected sub-bands thereof.Attorney Docket No.9833.7264.WO Notably, the transition band between the reflective and transmissive frequency ranges is much larger (in terms of percentage) than is the case with conventional passive / active antenna systems, allowing for improved performance by the frequency selective surfaces in terms of reflectivity and transmissivity in the frequency bands of interest.

[0062] FIG.3A is a schematic rear perspective view of a modular passive / active antenna system 300 according to embodiments of the present invention. The passive / active antenna system 300 includes a passive base station antenna 310 that can have two antenna modules 350 mounted on the rear side thereof. In some cases, the antenna modules 350 may comprise a passive mid-band linear array antenna module and a high-band active antenna module, while in other cases the antenna modules may comprise a mid-band active antenna module and a high- band active antenna module or two high-band active antenna modules. Other arrangements are also possible.

[0063] FIG.3B is a schematic plan view of the passive base station antenna 310 with the radome 312 thereof removed. The passive base station antenna system 310 has some similarities to the passive base station antenna 210 that is described above, so the description below will focus on the differences between the two passive base station antennas 310, 210.

[0064] The passive base station antenna 310 includes a reflector assembly 320 that is similar to the reflector assembly 220, but includes thinner (in the lateral direction) first and second reflector strips 324-1, 324-2 (which are barely visible in FIG.3B). In addition, the frequency selective surface 228-1 of passive base station antenna 210 that is configured to reflect RF energy in the 617-960 MHz and the 1427-2690 MHz frequency bands (or selected sub-bands thereof) while passing RF energy in the 3.1-4.2 GHz frequency band (or selected sub-bands thereof) is replaced in passive base station antenna 310 with a frequency selective surface 328-1 that is configured to reflect RF energy in the 617-960 MHz frequency band (or selected sub- bands thereof) while passing RF energy in the 1427-2690 MHz and 3.1-4.2 GHz frequency bands (or selected sub-bands thereof). Finally, passive base station antenna 310 does not include the first and second mid-band linear arrays 240-1, 240-2 of mid-band radiating elements 242 that are included in passive base station antenna 210, and is wider than passive base station antenna 210.

[0065] Still referring to FIG.3B, the passive base station antenna 310 includes first and second low-band linear arrays 330-1, 330-2 of low-band radiating elements 332 that that areAttorney Docket No.9833.7264.WO configured to operate in all or part of the 617-960 MHz frequency band. The low-band radiating elements 332 of the first low-band linear array 330-1 are mounted on the first reflector strip 324- 1, the main reflector 322 and the fourth reflector strip 324-4. The low-band radiating elements 332 of the second low-band linear array 330-2 are mounted on the second reflector strip 324-2, the main reflector 322 and the fifth reflector strip 324-5. The low-band linear arrays 330-1, 330- 2 may generate static antenna beams that provide coverage to a predefined coverage area. A first set of four RF ports 318-1 are provided that are used to connect the low-band arrays 330-1, 330-2 to remote radio heads that are mounted near the passive base station antenna 310.

[0066] The passive base station antenna 310 also includes a reflector assembly 320 that has first and second openings 326-1, 326-2. A first frequency selective surface 328-1 covers the first opening 326-1 and a second frequency selective surface 328-2 covers the second opening 326-2. The first frequency selective surface 328-1 may be designed to reflect RF signals in some or all of the 617-960 MHz frequency band while passing RF signals in, for example, some or all of the 2.0-2.7 GHz and 3.1-4.2 GHz frequency ranges. The second frequency selective surface 328-2 may be designed to reflect RF signals in some or all of the 617-960 MHz frequency band while passing RF signals in some or all of the 3.1-4.2 GHz frequency ranges. The second frequency selective surface 328-2 is shown by a dashed box to simplify FIG.3B.

[0067] As noted above, two antenna modules 350 may simultaneously be mounted behind passive base station antenna 310. Passive / active antenna system 300, unlike the prior- described passive / active antenna systems, employs a modular approach where different antenna modules 350 may be mounted behind the passive base station antenna 310 depending upon a cellular operators specific needs. Moreover, a cellular operator can change the capabilities by swapping out one antenna module 350 for another antenna module 350 and / or by initially deploying the passive base station antenna 310 with zero or one associated antenna modules 350 and later adding one or more additional antenna modules 350.

[0068] FIGS.3C-3F illustrate four example antenna modules that can be used in passive / active antenna system 300.

[0069] In particular, FIG.3C is a schematic plan view of a first antenna module 350-1 that may be mounted behind the first frequency selective surface 328-1 of passive base station antenna 310. As shown in FIG.3C, the first antenna module 350-1 includes a multicolumn beamforming array 360-1 that includes eight vertically-extending columns of mid-band radiatingAttorney Docket No.9833.7264.WO elements 342 that are configured to operate in, for example, the 1695-2690 MHz frequency band (or a subset thereof, such as the 2.5-2.7 GHz frequency band). The first antenna module 350-1 further includes a beamforming radio 370, a calibration circuit 372 that is used to calibrate the beamforming radio 370, a remote electronic tilt ("RET") actuator 380, a plurality of phase shifters 382, and a common mechanical linkage 384 that connects an output of the RET actuator 380 to the phase shifters 382. The RET actuator 380 may be configured to apply the same amount of movement to each phase shifter 382 so as to apply the same amount of electronic downtilt to the antenna beams formed by all eight columns of radiating elements 342 in beamforming array 360-1. Since the first frequency selective surface 328-1 of passive base station antenna 310 is configured to pass RF energy in the mid-band frequency range (or a portion thereof), beamforming array 360-1 may transmit and receive RF signals through the first frequency selective surface 328-1.

[0070] FIG.3D is a schematic plan view of a second antenna module 350-2 that may be mounted behind the second frequency selective surface 328-2 of passive base station antenna 310. As shown in FIG.3D, the second antenna module 350-2 includes a multicolumn beamforming array 360-2 that includes eight vertically-extending columns of high-band radiating elements 362 that are configured to operate in, for example, the 3.1-4.2 GHz frequency band (or a subset thereof). The second antenna module 350-2 also includes a beamforming radio 370, a calibration circuit 372 that is used to calibrate the beamforming radio 370, a RET actuator 380, a plurality of phase shifters 382, and a common mechanical linkage 384 that connects an output of the RET actuator 380 to the phase shifters 380. The second antenna module 350-2 may be identical to the active antenna module 250-1 included in passive / active antenna system 200. Since the second frequency selective surface 328-2 of passive base station antenna 310 is configured to pass RF energy in the high-band frequency range (or a portion thereof), beamforming array 360-2 may transmit and receive RF signals through the second frequency selective surface 328-2. Since the beamforming array 360-2 operates in a higher frequency band than the beamforming array 350-1 in the first antenna module 350-1, the radiating elements 362 are smaller than the radiating elements 362 in the first antenna module 350-1 and are also spaced closer together in both the row and column directions.

[0071] FIG.3E is a schematic plan view of a third antenna module 350-3 that may be mounted behind the first frequency selective surface 328-1 of passive base station antenna 310Attorney Docket No.9833.7264.WO instead of the first antenna module 350-1. The third antenna module 350-3 includes four linear arrays 340-1 through 340-4 of mid-band radiating elements 342 that are configured to generate static antenna beams that provide coverage to a sector such as, for example, a 120⁰ sector in the azimuth plane. The third antenna module 350-3 may include a second set of eight eight RF ports 318-2 that are used to couple the ports of one or more remote radio heads to the third antenna module 350-3. The third antenna module 350-3 does not include any calibration circuit since the module does not include a beamforming array. The third antenna module 350-3, however, may include at least two RET actuators 380 (or a multi-RET actuator), so that the electronic downtilts that are applied to the antenna beams generated by two of the mid-band linear arrays 340 may be set independently of the electronic downtilts that are applied to the antenna beams generated by other two of the mid-band linear arrays 340.

[0072] The eight columns of mid-band radiating elements 342 included in the beamforming array 360-1 of the antenna module 350-1 of FIG.3C may, for example, be spaced apart from each other by about 0.5 "center wavelengths," where the center wavelength is the wavelength corresponding to the center frequency of the operating frequency band of the beamforming array 360-1. This may improve or optimize the beam-scanning performance of the beamforming array 360-1, and also facilitates keeping the width of the beamforming array 360-1 from becoming so large that the passive / active antenna system 300 is commercially impractical. In contrast, the four mid-band linear arrays 340-1 through 340-4 that are included in the antenna module 350-3 of FIG.3E may, for example, be spaced apert by at least 0.6 center wavelengths, 2 / 3 center wavelengths or even 0.75 center wavelengths, where the center wavelength is the wavelength corresponding to the center frequency of the operating frequency band of the four mid-band linear arrays 340-1 through 340-4. This larger spacing may increase isolation between the four mid-band linear arrays 340-1 through 340-4 which may improve the performance thereof when operated using 2xMIMO, 4xMIMO or 8xMIMO communication techniques.

[0073] The passive / active antenna system 300 may be used as follows. Initially, a cellular operator may deploy the passive / active antenna system 300 with the third antenna module 350-3, or the second and third antenna modules 350-2, 350-3, mounted behind the passive base station antenna 310. The passive base station antenna 310 and the third antenna module 350-3 may provide 2G / 3G / 4G service. Notably, the passive base station antenna 310 and the third antenna module 350-3 may provide more 2G / 3G / 4G capabilities and improvedAttorney Docket No.9833.7264.WO service as compared to the passive base station antenna 210. In particular, the combination of passive base station antenna 310 and the third antenna module 350-3 provides four mid-band arrays 340 as compared to only two mid-band arrays 240 in passive / active antenna system 200, and the low-band and mid-band arrays in passive / active antenna system 300 may exhibit improved gain and / or better PIM performance since the frequency selective surfaces 328-1, 328- 2 may exhibit better selectivity than the frequency selective surfaces 228-1, 228-2 included in passive base station antenna 210.

[0074] At a later point in time, the cellular operator may decide to replace the third antenna module 350-3 with the first antenna module 350-1. In this configuration, the passive / active antenna system 300 includes the same capabilities as the passive / active antenna system 200 except that passive / active antenna system 300 does not include the two mid-band linear arrays 240 that are present in passive / active antenna system 200. However, in many cases, the cellular operator will not provide both sector and beamforming service in the mid-band frequency range, and hence the omission of the two mid-band linear arrays may have no consequence.

[0075] FIG.3F is a schematic plan view of a fourth antenna module 350-4 that may be mounted behind the passive base station antenna 310 instead of the third antenna module 350-3 of FIG.3E. The fourth antenna module 350-4 may be identical to the third antenna module 350- 3 except that the fourth antenna module 350-4 only includes two passive mid-band linear arrays 340-1, 340-2 instead of four passive mid-band linear arrays. In some situations, an operator may only require two passive mid-band linear arrays that generate sector antenna beams. Thus, having four passive mid-band linear arrays provides the operator no extra benefit. The fourth antenna module 350-4 may be lighter and lower cost than the third antenna module 350-3.

[0076] FIG.4 is a schematic plan view of an alternate passive base station antenna 310' that may be used in place of passive base station antenna 310 in passive / active antenna system 300. Passive base station antenna 310' may be identical to passive base station antenna 310 except that passive base station antenna 310' further includes first and second mid-band linear arrays 340-1, 340-2. The mid-band radiating elements 342 of the first mid-band linear array 340-1 are mounted on the main reflector panel 322 and on the fourth reflector strip 324-4, and the mid-band radiating elements 342 of the second mid-band linear array 340-2 are mounted on the main reflector panel 322 and on the fifth reflector strip 324-5. Each mid-band linear arrayAttorney Docket No.9833.7264.WO 340-1, 340-2 may optionally include one or more auxiliary mid-band radiating elements 342' that are offset in the horizontal direction from the other mid-band radiating elements 342 in the array 340. The auxiliary mid-band radiating elements 342' may be identical to the mid-band radiating elements 342 and are provided to increase the gain of the mid-band linear arrays 340 by narrowing the azimuth beamwidth of the antenna beams generated by the arrays 340. Passive base station antenna 310' also differs from passive base station antenna 310 in that it includes a second frequency selective surface 328-2' (shown schematically as a dashed box in FIG.4) that is configured to reflect low-band and mid-band RF energy while passing high-band RF energy, like the frequency selective surface 128 in active antenna module 150.

[0077] FIGS.5A-5C illustrate a modular passive / active antenna system 400 according to still further embodiments of the present invention. In particular, FIG.5A is a schematic side view of the modular passive / active antenna system 400 while FIG.5B is a schematic plan view of a passive base station antenna of the modular passive / active antenna system 400 with a radome thereof removed. FIG.5C is a schematic plan view of an antenna module that may be mounted behind the passive base station antenna of FIG.5B.

[0078] As shown in FIG.5A, the passive / active antenna system 400 includes a passive base station antenna system 410 and a pair of associated antenna modules 450 that are mounted behind the passive base station antenna 410.

[0079] Referring to FIG.5B, it can be seen that the passive base station antenna 410 is similar to the passive base station antenna 310. However, passive base station antenna 410 includes four short columns of mid-band radiating elements 342 that are mounted on the main reflector panel 322. In the depicted embodiment, each column of mid-band radiating elements 342 includes five mid-band radiating elements 342. In addition, while not visible in FIG.5B, the passive base station antenna 410 also includes a set of eight RF ports 318-2 that extend through the back surface of the radome 412 of passive base station antenna 410.

[0080] Referring to FIG.5C, an antenna module 450-3 is illustrated that may be mounted behind the first frequency selective surface 328-1 of passive base station antenna 410. The antenna module 450-3 may be identical to the third antenna module 350-3 described above with reference to FIG.3E, except that antenna module 450-3 includes first and second sets of RF ports 418-1, 418-2. The first set of RF ports 418-1 may be identical to the RF ports 318-2 included in the third antenna module 350-3 that are used to connect the four mid-band arraysAttorney Docket No.9833.7264.WO 340-1 through 340-4 to corresponding ports on remote radio heads that are external to the passive active antenna system 400. Each RF port in the second set of RF ports 418-2 may be used to connect an output of one of the phase shifters 382 in antenna module 450-3 to a respective one of the columns of mid-band radiating elements 342 included in passive base station antenna 410. In particular, each RF port 418-2 connects (through a power splitter) an output of a respective phase shifter 382 in antenna module 450-3 to the first or second polarization radiators of the five mid-band radiating elements 342 in a respective one of the four columns of mid-band radiating elements that are mounted on the main reflector panel 322 of passive base station antenna 410. A coaxial cable 408 (FIG.5A) may connect each RF port in the second set of RF ports 318-2 of passive base station antenna 410 to a respective one of the RF ports in the second set of RF ports 418-2 included in the third antenna module 450-3. As a result, the five mid-band radiating elements 342 in each column of mid-band radiating elements in passive base station antenna 410 is part of a respective one of the mid-band linear arrays 340 included in antenna module 450-3, thereby lengthening each mid-band array 340. This acts to increase the gain of the mid-band arrays 340 in antenna module 450-3. U.S. Patent No. 11,589,418, the entire content of which is incorporated herein by reference, discloses techniques for having linear arrays bridge two different antennas. The techniques that are described in U.S. Patent No.11,589,418 may be used to connect the mid-band radiating elements 342 in passive base station antenna 410 to the linear arrays 340 in antenna module 450-3.

[0081] While FIGS.5A-5C illustrate an embodiment where each column of mid-band radiating elements 342 in the passive base station antenna 410 is connected to a single output of a respective phase shifter 382 (for each polarization) in the passive antenna module 450-3, it will be appreciated that embodiments of the present invention are not limited thereto. In particular, additional RF ports may be provided in the passive base station antenna 410 and the passive antenna module 450-3 so that two or more outputs of each phase shifter 382 may be connected to the respective sub-sets of the mid-band radiating elements 342 in each column in the passive base station antenna 410. This provides increase control over the mid-band antenna beam shapes when downtilted.

[0082] 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 toAttorney Docket No.9833.7264.WO those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.

[0083] Spatially relative terms, such as "under," "below," "lower," "over," "upper," "top," "bottom," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features. Thus, the example term "under" can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0084] Herein, the terms "attached," "connected," "interconnected," "contacting," "mounted," "coupled," and the like can mean either direct or indirect attachment or coupling between elements, unless stated otherwise.

[0085] Well-known functions or constructions may not be described in detail for brevity and / or clarity. As used herein the expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0086] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. 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 in this specification, 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.

Claims

Attorney Docket No.9833.7264.WO CLAIMS:

1. An antenna system, comprising: a passive base station antenna that includes first and second arrays of first frequency band radiating elements and a first frequency selective surface that is reflective in the first frequency band and transmissive in a second frequency band; and a first antenna module that is mountable behind the first frequency selective surface, the first antenna module comprising at least first and second arrays of second frequency band radiating elements, wherein the first and second arrays of second frequency band radiating elements are configured to generate static antenna beams that provide coverage to a predefined sector.

2. The antenna system of Claim 1, wherein the first antenna module further comprises third and fourth arrays of second frequency band radiating elements that are configured to generate static antenna beams that provide coverage to the predefined sector.

3. The antenna system of Claim 2, wherein the first through fourth arrays of second frequency band radiating elements are configured to transmit and receive RF signals through the first frequency selective surface.

4. The antenna system of Claim 2, wherein the first antenna module further comprises a first remote electronic tilt ("RET") actuator that is operatively coupled to first and second phase shifters that are associated with the first array of second frequency band radiating elements and a second RET actuator that is operatively coupled to third and fourth phase shifters that are associated with the third array of second frequency band radiating elements.

5. The antenna system of any of Claims 1-4, wherein the first antenna module does not include a calibration circuit.

6. The antenna system of any of Claims 1-4, wherein the passive base station antenna further comprises a second frequency selective surface that is reflective in the first frequency band and transmissive in a third frequency band.Attorney Docket No.9833.7264.WO 7. The antenna system of Claim 6, wherein the third frequency band encompasses frequencies that are higher than the frequencies in the first and second frequency bands, and the second frequency band encompasses frequencies that are higher than the frequencies in the first frequency band.

8. The antenna system of Claim 7, wherein the second frequency selective surface is also reflective in the second frequency band.

9. The antenna system of Claim 8, further comprising a second antenna module that is mounted behind the second frequency selective surface, the second antenna module including a multicolumn beamforming array.

10. The antenna system of any of Claims 1-9, wherein the passive base station antenna further comprises a reflector assembly that has a first opening, and the first frequency selective surface extends over the first opening.

11. An antenna system, comprising: a passive base station antenna that includes first and second arrays of low-band radiating elements that are configured to operate in at least a portion of a 617-960 MHz frequency band; and a first antenna module that is mountable behind the passive base station antenna and configured to generate antenna beams that pass through the passive base station antenna, wherein the antenna system includes a first array of mid-band radiating elements that are configured to operate in at least a portion of a 1427-2690 MHz frequency band, where a first sub-set of the mid-band radiating elements in the first array are part of the passive base station antenna and a second sub-set of the radiating elements in the first array are part of the first antenna module.

12. The antenna system of Claim 11, the antenna system further comprising second through fourth arrays of mid-band radiating elements that are each configured to operate in at least a portion of the 1427-2690 MHz frequency band, where first sub-sets of the mid-band radiating elements in each of the second through fourth arrays are part of the passive base stationAttorney Docket No.9833.7264.WO antenna and second sub-sets of the radiating elements in the second through fourth arrays are part of the first antenna module.

13. The antenna system of Claims 11 or 12, wherein the passive base station antenna further comprises a first frequency selective surface that is configured to reflect RF energy in at least a portion of the 617-960 MHz frequency band and to pass RF energy in at least a portion of the 1427-2690 MHz frequency band, and the first antenna module is mounted behind the first frequency selective surface.

14. The antenna system of Claim 13, wherein the passive base station antenna further comprises a reflector assembly that has a main reflector and first and second reflector strips that define a first opening, and the first frequency selective surface extends over the first opening.

15. The antenna system of Claim 14, wherein the first sub-set of the mid-band radiating elements in the first array are mounted to extend forwardly from the main reflector.

16. The antenna system of any of Claims 11-15, wherein the first antenna module includes a phase shifter, and an output of the phase shifter is coupled to the second sub-set of the mid-band radiating elements in the first array.

17. An antenna system, comprising: a passive base station antenna that includes first and second arrays of low-band radiating elements that are configured to operate in at least a portion of a 617-960 MHz frequency band; and a passive antenna module that is mounted behind the passive base station antenna and configured to transmit and receive radio frequency ("RF") signals through the passive base station antenna.

18. The antenna system of Claim 17, wherein the passive antenna module comprises first through fourth arrays of mid-band radiating elements that are configured to operate in at least a portion of a 1427-2690 MHz frequency band.Attorney Docket No.9833.7264.WO 19. The antenna system of Claim 18, wherein each of the first through fourth arrays of mid-band radiating elements are configured to generate static antenna beams that provide coverage to a 120⁰ sector in an azimuth plane of the antenna system.

20. The antenna system of Claim 19, wherein the passive base station antenna includes a first frequency selective surface that is configured to reflect RF energy in at least a portion of the 617-960 MHz frequency band and to pass RF energy in at least a portion of the 1427-2690 MHz frequency band.

21. The antenna system of Claim 20, wherein the passive base station antenna further comprises a second frequency selective surface that is reflective in at least a portion of the 617- 960 MHz frequency band and transmissive in at least a portion of the 3.1-4.2 GHz frequency band.

22. The antenna system of any of Claims 17-21, wherein the passive antenna module does not include a calibration circuit.

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