Radiating element having feed handle with frequency selective surface and base station antenna comprising such radiating element

Abstract

A radiating element includes a feed shank and a radiator mounted on the feed shank. The feed handle includes a signal line and a ground line, the ground line including a frequency selective surface.

Description

Technical Field

[0001] The present invention relates generally to radio communications and, more particularly, to base station antennas for cellular communication systems and to radiating elements for such base station antennas. 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 in-line columns or columns in which some of the radiating elements are staggered horizontally. Most modern base station antennas include linear arrays of "low-band" radiating elements that support services in some or all of the 617-960 MHz frequency bands, and linear arrays of "mid-band" 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 linear array to transmit and receive RF signals with two orthogonal polarizations.

[0004] Each of the aforementioned linear arrays is coupled to two ports of a radio (one port for each polarization). The RF signal transmitted by the linear array is passed from the radio port to the antenna, where it is split into multiple 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 through the radiating elements to generate an antenna beam that covers a generally fixed coverage area, such as a sector of a cell. Because the antenna beam generated by the aforementioned 2G / 3G / 4G linear arrays generates a static antenna beam, the linear arrays are often referred to as "passive" linear arrays.

[0005] Most cellular operators are currently upgrading their networks to support fifth-generation (“5G”) cellular service. An important component of 5G cellular service is the use of so-called “active” beamforming arrays, which operate in conjunction with “active” 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 include multiple columns of radiating elements, with eight columns being the most common. Active beamforming arrays are typically formed using “high-band” radiating elements that operate in the higher frequency bands (e.g., some or all of the 3.1-4.2 GHz band and / or the 5.1-5.8 GHz band), but active beamforming arrays that operate in the higher portions of the mid-band frequency range (e.g., 2300-2690 MHz) may also be provided. Each column of radiating elements of such an active beamforming array is typically coupled to a corresponding port of a beamforming radio. The beamforming radio may be a separate device or may be integrated with the active antenna array. Beamforming radios can adjust the amplitude and phase of the RF signal subcomponents fed to each port of the radio to generate antenna beams with narrowed beamwidths (and therefore higher antenna gain) in the azimuth plane. These narrowed antenna beams can be electronically steered in the azimuth plane by properly selecting the amplitude and phase of the RF signal subcomponents.

[0006] To avoid having to increase the number of antennas at the cell site, the above-mentioned 5G antennas typically include passive linear arrays that support traditional 2G, 3G and / or 4G cellular services. In one popular solution, a 5G active antenna module (i.e., a module that includes an active beamforming array and associated beamforming radio equipment) is mounted on the rear surface of a passive base station antenna that includes multiple 2G, 3G and / or 4G passive linear arrays. Openings are provided in the reflector of the passive base station antenna so that the antenna beams generated by the active beamforming arrays can be transmitted through the passive base station antenna. Typically, some of the radiating elements of the 2G / 3G / 4G passive linear arrays are mounted in front of the radiating elements of the beamforming array. The above-mentioned antenna design is advantageous because the active antenna module can be removable, so as enhanced 5G capabilities are developed, cellular operators can replace the original active antenna module with an upgraded active antenna module without having to replace the passive base station antenna. In this document, the combination of a passive base station antenna with an active antenna module mounted thereon is referred to as a "passive / active antenna system." Summary of the Invention

[0007] According to an embodiment of the present invention, there is provided a radiating element including: a feeding stem having a signal line and a ground line, the ground line including a frequency selective surface; and a radiator mounted on the feeding stem.

[0008] In some embodiments, the signal line may overlap with the ground line.

[0009] In some embodiments, the frequency selective surface includes at least two spaced-apart metal layers.

[0010] In some embodiments, the signal line and the ground line together comprise an RF feed line configured to feed an RF signal to the radiator.

[0011] In some embodiments, the frequency selective surface comprises a bandpass filter.

[0012] In some embodiments, the frequency selective surface includes a plurality of unit cells, each unit cell including a first metal pattern and a second metal pattern positioned behind the first metal pattern. In some embodiments, the first metal pattern includes a cross pattern and / or the second metal pattern includes a polygonal pad. In some embodiments, the first metal pattern of each unit cell is galvanically coupled to the first metal pattern of a corresponding adjacent unit cell. In some embodiments, the second metal pattern of each unit cell is capacitively edge-coupled to the second metal pattern of a corresponding adjacent unit cell.

[0013] In some embodiments, the frequency selective surface can be configured to be at least 25% transparent (or at least 40% transparent) on average to RF energy in the upper operating frequency band.

[0014] In some embodiments, the ground line may include a plurality of longitudinally extending traces and a plurality of transversely extending traces interconnected to form a grid.

[0015] According to another embodiment of the present invention, a radiating element is provided, which includes: a dipole radiator; and a feed handle printed circuit board, the feed handle printed circuit board having a first metal layer, a second metal layer and a third metal layer, the first metal layer including a signal line configured to be connected to a first conductor of an RF transmission line, and the second metal layer configured to be connected to a second conductor of the RF transmission line.

[0016] In some embodiments, the feed handle printed circuit board further comprises a first dielectric substrate between the first metal layer and the second metal layer and a second dielectric substrate between the second metal layer and the third metal layer. In some embodiments, the second metal layer and the third metal layer together form a frequency selective surface.

[0017] In some embodiments, the second metal layer includes a ground line configured to couple to a second conductor of the RF transmission line. In some embodiments, the signal line and the ground line together comprise an RF feed line. In some embodiments, the frequency selective surface comprises a bandpass filter.

[0018] In some embodiments, the frequency selective surface includes a plurality of unit cells, each unit cell including a first metal pattern and a second metal pattern positioned behind the first metal pattern.

[0019] In some embodiments, the first metal pattern comprises a cross-shaped pattern, and the second metal pattern comprises a polygonal pad.

[0020] In some embodiments, the first metal pattern of each unit cell is galvanically coupled to the corresponding first metal pattern of the unit cell adjacent thereto, and the second metal pattern of each unit cell is capacitively edge coupled to the corresponding second metal pattern of the unit cell adjacent thereto.

[0021] According to another embodiment of the present invention, a base station antenna is provided, comprising a first radiating element configured as any of the aforementioned radiating elements, and a second radiating element configured to operate in a higher operating frequency band than the first radiating element. The frequency selective surface included in the first radiating element may include a bandpass filter having a passband that includes at least a portion of the higher operating frequency band.

[0022] In some embodiments, the first radiating element may be mounted in front of the second radiating element.

[0023] According to yet other embodiments of the present invention, base station antennas are provided, comprising: a first radiating element as part of a first array of radiating elements, the first array of radiating elements being configured to operate in a first operating frequency band; and a second radiating element as part of a second array of radiating elements, the second array of radiating elements being configured to operate in a second frequency band. In these antennas, the first radiating element comprises: a feed stem comprising an RF feed line; and a radiator coupled to the RF feed transmission line. The feed stem comprises a frequency selective surface configured to be at least 25% transparent, on average, to RF energy in the second frequency band.

[0024] In some embodiments, the RF feed line comprises a signal line and a ground line, and wherein at least a portion of the frequency selective surface forms the ground line.

[0025] In some embodiments, the frequency selective surface comprises a bandpass filter.

[0026] In some embodiments, the frequency selective surface includes a plurality of unit cells, each unit cell including a first metal pattern and a second metal pattern positioned behind the first metal pattern.

[0027] In some embodiments, each first metal pattern includes a corresponding cross-shaped pattern, and each second metal pattern includes a corresponding polygonal pad.

[0028] In some embodiments, the frequency selective surface comprises a metal pattern including longitudinally extending metal traces and laterally extending metal traces, and wherein the signal line overlaps one of the longitudinally extending metal traces.

[0029] In some embodiments, the base station antenna may further include a second frequency selective surface, wherein the first radiating element is mounted in front of the second frequency selective surface, and the second radiating element is mounted behind the second frequency selective surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1A is a schematic perspective view of a conventional low-band crossed-dipole radiating element.

[0031] Figure 1B yes Figure 1A Schematic side view of a conventional low-band crossed-dipole radiating element.

[0032] Figure 2A is a schematic perspective view of a passive / active antenna system including a passive base station antenna according to an embodiment of the present invention, which may be implemented using a low-band radiating element.

[0033] Figure 2B yes Figure 2A Schematic front view of a passive / active antenna system without its radome.

[0034] Figure 3A is a schematic perspective view of a low-frequency band radiation element according to an embodiment of the present invention.

[0035] Figure 3B yes Figure 3A A side view of a first feeding handle printed circuit board included in the feeding handle of the low-frequency band radiation element.

[0036] Figure 3C yes Figure 3A A schematic “top view” plan view of a first feed handle printed circuit board included in the feed handle of the low-frequency band radiation element.

[0037] Figure 3D yes Figure 3ASchematic plan view of a first feed stem printed circuit board included in a feed stem of a low-frequency band radiating element, wherein the first (top) metal layer and the first dielectric substrate of the first feed stem printed circuit board are removed to reveal the second (middle) metal layer.

[0038] Figure 3E yes Figure 3A A schematic “bottom-up” plan view of a first feed handle printed circuit board included in the feed handle of the low-frequency band radiation element.

[0039] Figure 3F yes Figure 3A A perspective view of the three unit cells of a frequency selective surface included in each feed shank of the radiating element of the printed circuit board.

[0040] Figure 4 yes Figures 3A-3F Graphs of the S1:1 and S1:2 transmission characteristics of the ground wire of the low-frequency band radiating element. DETAILED DESCRIPTION

[0041] The passive / active antenna systems described above allow cellular operators to support both legacy 2G / 3G / 4G cellular services and 5G cellular services using a single base station antenna system. Unfortunately, however, in practice, the radiating elements of the passive 2G / 3G / 4G array mounted in front of the 5G beamforming array can cause the antenna beam generated by the beamforming array to "scatter." Scattering is undesirable because it can reduce the gain of the 5G antenna beam by changing its shape in both the azimuth and elevation planes. For example, scattering tends to negatively impact the beamwidth, beam shape, pointing angle, gain, and front-to-back ratio of the 5G antenna beam.

[0042] Two different types of scattering can occur. First, the conductive structures of the radiating elements of the lower frequency (passive) arrays mounted in front of the 5G beamforming array can reflect the RF energy transmitted by the radiating elements of the beamforming array. Some of this reflected RF energy can then exit the base station antenna in an undesirable direction (possibly after further reflection from other metallic structures in the base station antenna, such as reflectors, etc.), or it can exit the base station antenna in a desired direction, but with a phase that causes the reflected RF energy to destructively combine with non-reflected RF energy. The end result is that when the RF energy transmitted by the beamforming array reflects from the radiating elements of the passive 2G / 3G / 4G linear arrays, these reflections typically distort the radiation pattern generated by the beamforming array in an undesirable manner.

[0043] The second type of scattering occurs when the conductive structure of the radiating elements of the passive 2G / 3G / 4G linear array has an electrical length that causes the structure to resonate within the operating frequency band of the 5G beamforming array. For example, the conductive structure of the radiating elements of one of the passive (lower band) arrays may resonate within the operating frequency band of the 5G beamforming array if the electrical length of the conductive structure is approximately 1 / 2 wavelength or approximately a full wavelength of a frequency within the operating frequency band of the 5G beamforming array. In many cases, the operating frequency band of the beamforming array may be approximately four times the frequency within the operating frequency band of the passive low-band linear array and approximately twice the frequency within the operating frequency band of the passive mid-band linear array. Because the dipole arms of the radiating elements of the low-band linear array typically have an electrical length of approximately 1 / 4 of the center wavelength of the low-band operating frequency range, they may have a resonant length relative to the RF energy emitted by the 5G beamforming array. Thus, the RF energy transmitted by the 5G beamforming array can couple to, for example, the dipole arms of a nearby low-band radiating element, and the higher-band currents developed in these dipole arms produce additional high-band radiation that distorts the antenna beam produced by the linear array of low-band radiating elements.

[0044] So-called "cloaking" radiating elements are known in the art and have dipole arms that are designed so that high-band currents are not formed thereon to a significant extent in response to RF radiation within a preselected frequency range. These radiating elements can reduce or eliminate the second of the above-mentioned types of scattering of higher-band radiation by the dipole arms of nearby lower-band radiating elements. The present invention is based in part on the recognition that the feed stems of the lower-band radiating elements can also cause both of the above-mentioned types of scattering. The feed stem of a cross-dipole radiating element refers to the structure that feeds RF signals to and from the dipole arms of the radiating element. In most cases, the dipole arms are mounted on the distal (front) end of the feed stem, and the base (rear) end of the feed stem is mounted on the reflector of the base station antenna or on a feed board printed circuit board, which is mounted on the reflector.

[0045] The feed stem of the low-band radiating element may include multiple metal patterns that can reflect high-band RF radiation emitted by the high-band beamforming array mounted behind the low-band radiating element (i.e., the feed stem of the low-band radiating element can cause the first type of scattering discussed above). Such reflection can degrade the shape and characteristics of the antenna beam formed by the high-band beamforming array. In addition, the feed stem of the low-band radiating element typically also has a metal structure with a length of approximately 1 / 4 of the center wavelength of the low-band operating frequency range. Therefore, the feed stem of the low-band radiating element can also cause the second type of scattering discussed above with respect to RF radiation emitted by the 5G beamforming array. Although the amount of scattering caused by the feed stem is often much lower than the scattering caused by non-stealth low-band dipole arms, the amount of scattering may still be significant enough to distort the antenna beam formed by the 5G beamforming array.

[0046] According to an embodiment of the present invention, a base station antenna is provided, comprising a low-band radiating element having a feed handle including one or more frequency-selective surfaces. These frequency-selective surfaces can be configured to at least partially transmit RF radiation within the operating frequency band of a high-band radiating element included in the base station antenna. As a result, RF radiation emitted by the high-band radiating element and directed in the direction of the low-band radiating element may experience less scattering from the low-band radiating element.

[0047] In some embodiments, each frequency selective surface may include a portion of an RF feed line disposed on a feed handle of a low-band radiating element. The RF feed line may include a signal line and a ground line. The signal line may be configured to couple to a first conductor of an RF transmission line that feeds the first radiating element, and the ground line may be configured to couple to a second conductor of the RF transmission line that feeds the low-band radiating element. In some embodiments, the ground line may be implemented as a frequency selective surface. Thus, the metal forming the ground line may cause less scattering of RF signals emitted by the high-band radiating element because the ground line may be partially transparent to RF radiation in the high-band operating frequency band. In some embodiments, the frequency selective surface may have a bandpass frequency response. In such embodiments, the frequency selective surface may, for example, be configured to pass at least 25% (on average) of the incident RF energy in the high-band operating frequency band, and more preferably may be configured to pass at least 40% (on average) of the incident RF energy in the high-band operating frequency band.

[0048] In some embodiments, the RF feed line may include three stacked metal layers, namely a first metal layer including a signal line, and second and third metal layers forming a ground line having a frequency selective surface. The feed stem may be conveniently formed using a multilayer feed stem printed circuit board comprising three metallization layers separated from each other by a first dielectric substrate and a second dielectric substrate, but it should be understood that embodiments of the present invention are not limited to feed stem printed circuit board implementations.

[0049] The frequency selective surface may include a plurality of unit cells electrically connected to each other. Each unit cell may include a first metal pattern implemented in a first metal layer and a second metal pattern implemented in a second metal layer, such that the second metal pattern overlaps the first metal pattern. Each first metal pattern may include, for example, a metal pad (e.g., a polygonal metal pad). The metal pads of adjacent unit cells may be spaced apart from each other such that adjacent unit cells are electrically coupled via edge capacitance between the metal pads of adjacent unit cells. Each second metal pattern may include, for example, two intersecting metal lines forming a cross. The cross-shaped metal lines of adjacent unit cells may be galvanically coupled to each other such that the second metal layer includes a grid of intersecting longitudinally extending metal traces and laterally extending metal traces.

[0050] Radiating elements according to embodiments of the present invention may be included in multi-band base station antennas and may reduce the amount of interaction between arrays in different frequency bands. Base station antennas including radiating elements according to embodiments of the present invention may be used, for example, as sector antennas in the aforementioned cellular communication systems.

[0051] Before discussing radiating elements according to embodiments of the present invention, it is helpful to discuss the design and operation of a representative conventional low-band radiating element for a base station antenna.

[0052] Figure 1A is a perspective view of a conventional low-band crossed-dipole radiating element 1 . Figure 1B is a shaded side view of the crossed dipole radiating element 1 showing the metallization pattern on the first feed shank printed circuit board 20 - 1 of the radiating element 1 . Figure 1B In FIG, the solid line is the metallization pattern on the first side of the feed handle printed circuit board 20 - 1 , and the dashed line is the metallization pattern on the second (opposite) side of the feed handle printed circuit board 20 - 1 . Figure 1B In the embodiment, since the main surface of the feed handle printed circuit board 20-2 is perpendicular to the viewing angle, only the side surface of the second feed handle printed circuit board 20-2 is visible. It should be noted that in this document, the same elements can be individually referenced by their full reference numerals (e.g., feed handle printed circuit board 20-2) and can be collectively referenced by the first part of their reference numerals (e.g., feed handle printed circuit board 20).

[0053] like Figure 1AAs shown in FIG, a conventional cross-dipole radiating element 1 includes a feed stem 10 and a pair of dipole radiators 70-1, 70-2. The feed stem 10 includes a first feed stem printed circuit board (PCB) and a second feed stem printed circuit board (PCB) 20-1, 20-2. Each feed stem PCB 20-1, 20-2 includes a corresponding RF feed line 16-1, 16-2 that transmits RF signals between a first RF transmission line and a second RF transmission line (not shown) connected to the radiating element 1 to transfer RF signals to and from the radiating element 1. Each such RF transmission line may comprise, for example, a coaxial cable or a microstrip transmission line on the feed stem PCB.

[0054] refer to Figure 1A and 1B Each feed handle PCB 20 has a base 22 and a distal end 24 positioned forward of the base 22. The first feed handle PCB 20-1 includes a slit 26 extending forward from its base 22, and the second feed handle PCB 20-2 includes a slit 26 extending rearward from its distal end 24. The feed handle PCBs 20-1 and 20-2 are arranged perpendicular to each other with their slits 26 engaged, so that the two mated feed handle PCBs 20-1, 20-2 have a cross shape when viewed from the front.

[0055] The rear portion of each feed handle PCB 20 may include a protrusion that is inserted through a slot (not shown) in the feed board PCB. The metallized pads on the protrusion can be soldered to the metallized pads on the feed board PCB to mechanically mount the radiating element 1 on the feed board PCB and electrically connect the RF feed lines 16-1, 16-2 on the feed handle 10 to the RF transmission lines on the feed board PCB.

[0056] The dipole radiators 70-1, 70-2 are positioned at the distal end 24 of the feed handle printed circuit board 20 and can be (and typically are) physically mounted on the feed handle printed circuit board 20. The first dipole radiator 70-1 extends along a first axis and the second dipole radiator 70-2 extends along a second axis that is substantially perpendicular to the first axis. The first dipole radiator 70-1 includes a first dipole arm and a second dipole arm 80-1, 80-2, and the second dipole radiator 70-2 includes a third dipole arm and a fourth dipole arm 80-3, 80-4. The dipole radiators 70-1, 70-2 can be formed in a dipole radiator printed circuit board 82. The dipole arm 80 is a stealth dipole arm formed as a series of widened metal segments 84 interconnected by narrow metal traces 86 (see FIG. 1 ). Figure 1A). Dipole radiators 70-1, 70-2 are shown as having an elongated "figure-8" shape, with each dipole arm 80 formed as a loop. A variety of dipole arms are known in the art, including those having many different shapes or formed in different ways (e.g., using metal plates). It should be understood that radiating elements according to embodiments of the present invention having the feed shank design disclosed herein can have any suitable dipole arm design, including dipole arms having any shape, such as formed in any of the ways discussed above.

[0057] The dipole arms 80-1 and 80-2 of the first dipole radiator 70-1 are center-fed by the first RF feed line 16-1 on the first feed handle printed circuit board 20-1 and radiate together at a first polarization. In the depicted embodiment, the first dipole radiator 70-1 is designed to transmit and receive signals having a +45° linear polarization. The dipole arms 80-3 and 80-4 of the second dipole radiator 70-2 are center-fed by the second RF feed line 16-2 on the second feed handle printed circuit board 20-2 and radiate together at a second polarization orthogonal to the first polarization. The second dipole radiator 70-2 is designed to transmit and receive signals having a tilted -45° linear polarization.

[0058] like Figure 1B As shown in FIG, a two-wire transmission line structure is formed on the second side of the feed handle printed circuit board 20-1. The two-wire transmission line structure includes first and second ground lines 30-1 and 30-2, which are implemented as first and second metallized areas extending from the base 22 of the first feed handle printed circuit board 20-1 to the distal end 24 thereof. Each ground line 30-1 and 30-2 is connected to a ground conductor (not shown) of a first RF transmission line that feeds the radiating element 1. The connection between the first and second ground lines 30-1 and 30-2 and the ground conductor of the first RF transmission line can be at the base 22 of the first feed handle printed circuit board 20-1. The first and second ground lines 30-1 and 30-2 can each have an electrical length of approximately 1 / 4 of the center wavelength of the radiating element 1.

[0059] A signal line 40 is formed on a first side of the feed handle printed circuit board 20-1. The signal line 40 is connected to a signal conductor of an RF transmission line that feeds the first feed handle printed circuit board 20-1. The signal line 40 extends forward from the base 22 of the first feed handle printed circuit board 20-1 and travels approximately two-thirds of the way toward its distal end 24. The signal line 40 then makes a first 90° turn to extend laterally across the first side of the feed handle printed circuit board 20-1. Finally, the signal line 40 makes a second 90° turn to extend rearward toward the base 22 of the first feed handle printed circuit board 20-1.

[0060] The signal line 40 includes a forward extending segment 42-1, a laterally extending segment 42-2, and a rearward extending segment 42-3. The forward extending segment 42-1 overlaps the first ground line 30-1. In this document, two elements "overlap" if an axis perpendicular to the main surface of the printed circuit board intersects with the two elements on the printed circuit board (or equivalent structure). The laterally extending segment 42-2 extends from the end of the forward extending segment 42-1 to span the gap 36 (i.e., the unmetallized area) provided between the first and second ground lines 30-1, 30-2. The laterally extending segment 42-2 partially overlaps with both the first ground line 30-1 and the second ground line 30-2. The rearward extending segment 42-3 extends from the end of the laterally extending segment 42-2 rearwardly toward the base 22 of the first feed handle printed circuit board 20-1 at right angles. The rearward extending segment 42-3 overlaps with the second ground line 30-2.

[0061] As discussed above, according to embodiments of the present invention, a cross-dipole radiating element is provided, having a feed stem that is at least partially transparent to RF energy in the operating frequency band of one or more nearby higher-band radiating elements. In particular, the radiating element according to embodiments of the present invention can have a first ground line and a second ground line implemented as a frequency selective surface that is at least partially transparent in the operating frequency band of the nearby higher-band radiating elements. Thus, the feed stem of the radiating element according to embodiments of the present invention can cause less scattering of RF energy emitted by the nearby higher-band radiating elements, which can improve the peak directivity and antenna beam shape of the nearby higher-band radiating elements.

[0062] The following discussion of crossed-dipole radiating elements according to embodiments of the present invention will focus on low-band radiating elements having a feed stem that is partially transparent to RF radiation emitted by, for example, nearby high-band radiating elements. However, it will be appreciated that the techniques disclosed herein can be used, for example, to provide mid-band radiating elements that are partially transparent to RF radiation emitted by nearby high-band radiating elements, or in any other suitable application. Thus, while radiating elements according to embodiments of the present invention will be described below as low-band radiating elements, it will be appreciated that they can alternatively be reduced in size to operate as, for example, mid-band radiating elements.

[0063] Before describing exemplary embodiments of the radiating element of the present invention, an exemplary base station antenna in which the radiating element according to embodiments of the present invention may be used will first be described.

[0064] Figures 2A-2B 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 2Ais a schematic rear perspective view of the passive / active antenna system 100, and Figure 2B The antenna covers of both the passive base station antenna 110 and the active antenna module are omitted. Figure 2A A schematic perspective view of a passive / active antenna system 100 is shown. Figure 2A and Figure 2B , the axes illustrate the longitudinal (L), transverse (T), and forward (F) directions of the base station antenna system 100. In the following description, the antenna 100 and the radiating elements included therein will be described using the following terms that assume that the antenna 100 is mounted on a tower for normal use, wherein the longitudinal axis of the antenna 100 extends along a vertical axis and the front surface of the antenna 100 is mounted opposite the tower pointing toward the coverage area of the antenna 100.

[0065] refer to Figure 2A , the passive / active antenna system 100 can be mounted on, for example, an antenna tower 102 using mounting hardware 104. The active antenna module 150 can be mounted directly on the rear surface of the passive base station antenna 110, or can be held in place behind the passive base station antenna 110 by the mounting hardware 104. 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 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 radio devices (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 be later replaced with a different active antenna module.

[0066] refer to Figure 2BThe passive base station antenna 110 includes a reflector assembly 120. The reflector assembly 120 may be referred to herein as a "passive reflector assembly" because it is part of the passive base station antenna 110. The passive reflector assembly 120 includes a main reflector 122 and first and second spaced-apart reflector strips 124-1 and 124-2 that extend longitudinally 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 that extends in a transverse direction between the top ends of 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 can be defined by the top portion of the main reflector 122, the first and second reflector strips 124-1, 124-2, and the third reflector strip 124-3. At least the main reflector 122 can include or comprise a metal surface (e.g., a sheet of aluminum) that acts as a reflector and a ground plane for the radiating elements of the antenna 100. Various mechanical and electronic components (not shown) of the antenna can be mounted behind the passive reflector assembly 120, such as phase shifters, remote electronic tilt units, mechanical linkages, controllers, duplexers, etc.

[0067] The passive base station antenna 110 also includes a plurality of passive linear arrays of radiating elements extending forward from the passive reflector assembly 120. The linear arrays may support, for example, 2G, 3G, and / or 4G cellular services. Figures 2A-2B In the exemplary passive base station antenna 110 shown in FIG, the linear arrays include first and second low-band linear arrays 130-1 and 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 and mid-band linear arrays 130, 140 can generate relatively static antenna beams (e.g., antenna beams each configured to cover a sector of a base station) that provide coverage to a predefined coverage area, 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 a cell).

[0068] 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 a first polarization radiator of a radiating element in one of the linear arrays, and the second RF port 118 is connected between a second port of the radio device and a second polarization radiator of a radiating element in the linear array. An RF signal to be transmitted by a selected one of the linear arrays 130, 140 is passed from the radio(s) 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 that are fed to corresponding first or second radiators of the radiating elements in the linear array, where the sub-components of the RF signal are radiated into free space.

[0069] The low-band radiating elements and / or mid-band radiating elements 132, 142 may be mounted on a feed board printed circuit board that couples RF signals to and from the respective radiating elements 132, 142. Figure 2B , mid-band radiating elements 142 are shown mounted in pairs on a plurality of mid-band feed board printed circuit boards 148. (Low-band radiating elements are also mounted on the feed board printed circuit boards, but they are not visible in the figure.) Cables can be used to connect each feed board printed circuit board 148 to other components of the antenna, such as a duplexer, phase shifters, etc.

[0070] Most of the low-band and mid-band radiating elements 132, 142 are mounted to extend forward from the main reflector 122. However, the low-band linear arrays 130-1, 130-2 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 can provide mounting locations for the low-band radiating elements 132 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 and second reflector strips 124-1, 124-2 and the main reflector 122 are maintained at a common ground voltage, which can improve the performance of the low-band linear arrays 130-1, 130-2.

[0071] Each low-band radiating element 132 may include a tilted -45° / +45° cross-dipole radiating element including a tilted -45° polarized dipole radiator 134-1 and a tilted +45° polarized dipole radiator 134-2. The dipole radiators 134-1, 134-2 may be mounted on a feed stem (not shown). In some cases, the three uppermost low-band radiating elements 132 above the main reflector 122 may be mounted on a frequency selective surface covering the opening 126. This frequency selective surface is described in more detail below. In other cases, the low-band radiating elements 132 may include a tilted feed stem that allows these radiating elements to be mounted on the first and second reflector strips 124-1, 124-2 with the dipole radiators 134 of these radiating elements 132 in front of the opening 126. Each low-band radiating element 132 has a dipole radiator 134 designed to be substantially transparent to the RF energy emitted by the mid-band radiating element 142 .

[0072] Active antenna module 150 includes a multi-column beamforming array 160 of radiating elements 162 and a beamforming radio (not visible in the figure). Multi-column beamforming array 160 may be mounted in the front portion of active antenna module 150, and the beamforming radio may be mounted behind 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 (e.g., in the 3.1-3.6 GHz frequency band). High-band radiating elements 162 are mounted to extend forward from reflector 154 (herein referred to as the "active reflector") of active antenna module 150. The beamforming radio is capable of electronically adjusting 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 a beamforming radio may be coupled to a column of radiating elements of the beamforming array 160, and the amplitude and phase of the subcomponents of the RF signal fed to 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.

[0073] The beamforming array 160 of the active antenna module 150 is mounted behind the opening 126 in the passive reflector assembly 114. The beamforming array 160 is Figure 2B It can be seen in Figure 2B The radomes of the passive base station antenna 110 and the active antenna module 150 are omitted. 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 to provide service to the coverage area of the passive / active antenna system 100.

[0074] As discussed above, a frequency selective surface (not shown) can cover the opening 126. The frequency selective surface can be configured to allow RF energy emitted by the high-band radiating elements 162 in the beamforming array 160 to pass therethrough, while reflecting RF energy in the lower frequency bands (and specifically, the low-band RF signals emitted by the low-band radiating elements 132). The frequency selective surface can be coplanar with the opening 126, in front of the opening 126, or behind the opening 126. The frequency selective surface can have a grid pattern, such as a grid of metal pads and / or other metal structures. The grid pattern can be arranged in any suitable manner and can be symmetrical or asymmetrical across the width and / or length of the frequency selective surface. The grid pattern can include sub-wavelength periodic microstructures. The metal pads / structures can be arranged in one or more layers. The frequency selective surface can be formed on a substrate (e.g., a printed circuit board or metal plate). In some embodiments, the frequency selective surface can include a portion of the passive reflector assembly 120 that is stamped to form a metal grid structure therein. In such cases, “openings 126 ” comprise a large number of small openings that act as large openings relative to the RF energy in the operating frequency band of the beamforming array 160 .

[0075] Figures 2A-2B One difficulty with the passive / active base station antenna system 100 is that some of the low-band radiating elements 132 are mounted directly in front of the high-band beamforming array 160. Consequently, the metallic elements of the low-band radiating elements 132 may partially block / reflect the RF radiation emitted by the high-band beamforming array 160, and / or the high-band RF radiation may induce currents in the metallic elements of the low-band radiating elements 132, which may then re-radiate the high-band radiation in a manner that distorts the shape of the antenna beam generated by the high-band beamforming array 160.

[0076] Figure 3A is a perspective view of a low-band radiation element 200 according to an embodiment of the present invention. Figure 3B FIG. 2 is a side view of the first feeding stem printed circuit board 220 - 1 included in the feeding stem 210 of the low-frequency band radiation element 200 . Figures 3C-3E yes Figure 3A A schematic plan view of three metallization layers included on the first feed handle printed circuit board 220-1 included in the radiation element 200. Finally, Figure 3F yes Figure 3A A perspective view of three unit cells of a frequency selective surface included in each feed handle printed circuit board 220 of the radiating element 200. For example, the low-band radiating element 132 of the base station antenna 100 can be implemented using the low-band radiating element 200.

[0077] refer to Figure 3A The low-frequency band radiating element 200 includes a feed handle 210, a first dipole radiator 270-1, and a second dipole radiator 270-2. The feed handle 210 includes a first feed handle printed circuit board and a second feed handle printed circuit board 220-1, 220-2. Each feed handle printed circuit board 220 has a base 222 and a distal (front) end 224 positioned in front of the base 222. The first feed handle printed circuit board 220-1 includes a slit 226 extending rearward from its distal end 224 (see FIG. 2 ). Figure 3B ), and the second feed handle printed circuit board 220-2 includes a slit 226 extending forward from its base 222. The feed handle printed circuit boards 220-1 and 220-2 are arranged perpendicular to each other, wherein the slits 226 in the two feed handle printed circuit boards 220 receive each other, so that when viewed from the front, the two mating printed circuit boards 220-1, 220-2 have a cross shape.

[0078] Each feed shank printed circuit board 220-1, 220-2 includes a corresponding RF feed line 240-1, 240-2 that transmits RF signals between the first and second RF transmission lines (not shown) of radiating element 200 and the corresponding cross-dipole radiator 270-1, 270-2. Each RF feed line 240 includes a signal line 242 and a pair of ground lines 246-1, 246-2, which are discussed in more detail below. Each RF transmission line (not shown) can include, for example, a coaxial cable or a microstrip transmission line on the feed shank printed circuit board. Each RF transmission line transmits RF signals between radiating element 200 and other components of the base station antenna, including radiating element 200.

[0079] The dipole radiators 270-1, 270-2 are mounted adjacent to (and typically on) the distal end 224 of the feed handle printed circuit board 220. The first dipole radiator 270-1 includes a first dipole arm and a second dipole arm 280-1, 280-2, and the second dipole radiator 270-2 includes a third dipole arm and a fourth dipole arm 280-3, 280-4. The dipole radiators 270 and dipole arms 280 may be similar to those described above with reference to FIG. Figures 1A-1B The described dipole radiator 70 and dipole arm 80 are identical, and therefore, further description thereof will be omitted herein.

[0080] As described above, respective RF feed lines 240-1, 240-2 are formed in the first and second feed stem PCBs 220-1, 220-2. Each RF transmission line structure 240 includes a signal line 242 and a pair of ground lines 246-1, 246-2. Figures 3B-3F The design of one of the RF feed lines 240 is shown in more detail.

[0081] First reference Figure 3B , it can be seen that each feed handle printed circuit board 220 can be implemented using a multilayer printed circuit board 230, which includes a first and second dielectric substrates 232-1, 232-2 and a first metal layer 234-1 to a third metal layer 234-3. The first metal layer 234-1 is formed on the outer surface of the first dielectric substrate 232-1, and the third metal layer 234-3 is formed on the outer surface of the second dielectric substrate 232-2. The second metal layer 234-2 is formed on the inner surface of one of the first dielectric substrate 232-1 and the second dielectric substrate 232-2. For ease of description, in this document, the first metal layer 234-1 may also be referred to as the "top" metal layer, the third metal layer 234-3 may also be referred to as the "bottom" metal layer, and the second metal layer 234-2 may be referred to as the "middle" metal layer.

[0082] Figure 3C FIG. 2 is a schematic “top” plan view of the first feed handle printed circuit board 220-1 showing the first (top) metal layer 234-1 formed on the outer (top) surface of the first dielectric substrate 232-1. Figure 3C As shown in FIG, the top metal layer 234-1 may include a signal line 242 of the RF feed line 240. The signal line 242 may be galvanically coupled to a signal conductor of an RF transmission line (not shown) that feeds the first feed handle printed circuit board 220-1, typically at the base 222 of the first feed handle printed circuit board 220-1. The signal line 242 extends forward from the base 222 of the first feed handle printed circuit board 220-1 and travels approximately two-thirds of the way toward the distal end 224 of the first feed handle printed circuit board 220-1. The signal line 242 then makes a first 90° turn to extend laterally across the first side of the first feed handle printed circuit board 220-1. Finally, the signal line 242 makes a second 90° turn to extend rearward toward the base 222 of the first feed handle printed circuit board 220-1. Thus, the signal line 242 includes a forward extending segment 244-1, a laterally extending segment 244-2, and a rearward extending segment 244-3. The forward-extending section 244-1 includes a widened pad region near the base of the first feed handle printed circuit board 220-1 and a narrower trace extending forward from the widened pad region. The laterally-extending section 244-2 extends from the end of the forward-extending section 244-1 to span the gap 236 (i.e., the unmetallized area) provided between the first and second ground lines 246-1 and 246-2. The rearward-extending section 244-3 includes a narrow trace extending at a right angle from the end of the laterally-extending section 244-2 toward the base 222 of the first feed handle printed circuit board 220-1.

[0083] Figure 3D is a schematic plan view of the first feed handle printed circuit board 220 - 1 with the first (top) metal layer 234 - 1 and the first dielectric substrate 232 - 1 removed to illustrate the second (middle) metal layer 234 - 2 and the second dielectric substrate 232 - 1 . Figure 3E is a schematic “bottom” plan view of the first feed handle printed circuit board 220 - 1 showing the third (bottom) metal layer 234 - 3 formed on the outer (bottom) surface of the second dielectric substrate 232 - 2 . Figure 3D and 3E The structure of the first and second ground lines 246-1, 246-2 of the RF transmission line structure 240 is shown. The first and second ground lines 246-1, 246-2 are implemented as frequency selective surfaces formed on the middle and bottom layers 234-2, 234-3 of the first feed handle printed circuit board 220-1.

[0084] like Figure 3D As shown in FIG, the intermediate metal layer 234-2 includes two grids of longitudinally extending metal traces 248 and transversely extending metal traces 250. In the depicted embodiment, each grid includes a total of three longitudinally extending metal traces 248 and eight transversely extending metal traces 250. The longitudinally extending metal traces 248 can extend substantially from the base 222 of the first feed handle printed circuit board 220-1 to its distal end 224. However, it should be appreciated that embodiments of the present invention are not limited in this regard. The grids of longitudinally extending metal traces 248 and transversely extending metal traces 250 can be as follows: Figures 1A-1B The dual ground wires 30 - 1 , 30 - 2 on the feeding handle 10 of the conventional low-frequency band radiating element 1 function similarly.

[0085] The forward-extending segment 244-1 of the signal line 242 may overlap the middle longitudinally extending metal trace 248 of the first ground line 246-1. The backward-extending segment 244-3 of the signal line 242 may overlap the middle longitudinally extending metal trace 248 of the second ground line 246-2.

[0086] like Figure 3E As shown in FIG, the bottom metal layer 234-3 includes two groups of metal pads 252. Each group of metal pads 252 includes three columns of metal pads 252, wherein each column extends in the longitudinal direction of the feed handle printed circuit board 220-1. In the depicted embodiment, each column includes eight metal pads 252, but it should be understood that embodiments of the present invention are not limited thereto and that more or fewer than three columns of metal pads 252 may be provided. Each longitudinally extending metal trace 248 in the intermediate metal layer 234-2 may overlap with a corresponding one of the columns of metal pads 252 included in the bottom metal layer 234-3.

[0087] Each ground line 246-1, 246-2 is coupled to a ground conductor (not shown) of the first feed transmission line for radiating element 200. In particular, one or more of the longitudinally extending metal traces 248 in each grid of the second metal layer 234-2 can be galvanically connected to the ground conductor of the first feed transmission line (not shown) for radiating element 200 at the base 222 of the first feed handle printed circuit board 220-1. The metal pad 252 in the third metal layer 234-3 can be capacitively coupled to the second metal layer 234-2. The second metal layer 234-2 can also be galvanically connected to one or more of the dipole arms 280.

[0088] The second feed handle printed circuit board 220-2 may have substantially the same design as the first feed handle printed circuit board 220-1, except that the slit 226 in the second feed handle printed circuit board 220-2 extends forward from the base 222 of the second feed handle printed circuit board 220-2 rather than extending rearward from the distal end 224 thereof, as is the case with the slit 226 in the first feed handle printed circuit board 220-1, and the signal line 242 on the second feed handle printed circuit board 220-2 extends further forward before being bent to form a U-shape, so that the signal line 242 can extend through the slit 226. Therefore, further description of the second feed handle printed circuit board 220-2 will be omitted herein.

[0089] Reference again Figure 1B , it can be seen that the first and second grounding wires 20-1, 20-2, which are part of the feeding handle 10 of the conventional low-frequency band radiating element 1, each include a large metallized area. Figures 2A-2B When the passive / active antenna system 100 includes a linear array of low-band radiating elements 1, the ground wire 20 may reflect RF radiation emitted by the high-band beamforming array 160 (i.e., may cause the first type of scattering), particularly when the high-band beamforming array 160 is electronically scanned in the azimuth plane. Furthermore, the first and second ground wires 20-1, 20-2 may each have a length of approximately ¼ of the center wavelength of the radiating element 1, and thus may have a length of approximately one wavelength for frequencies within the operating frequency range of the high-band beamforming array 160. Consequently, high-band currents may be generated on the ground wire 20 in response to the RF radiation emitted by the high-band beamforming array 160, and the ground wire 20 may then emit high-band radiation in response to these currents, meaning that the conventional feed handle 10 may also cause the second type of scattering discussed above.

[0090] According to an embodiment of the present invention, the first and second ground wires 246-1 and 246-2 provided on each feed shank printed circuit board 220 of the low-band radiating element 200 are implemented using corresponding frequency selective surfaces. These frequency selective surfaces can be configured to be at least 25% transparent to RF radiation in the operating frequency band of the high-band beamforming array 160, and more preferably at least 40% transparent. As a result, the ground wires 246-1 and 246-2 can reflect less RF radiation emitted by the high-band beamforming array 160 and thus have less impact on the antenna beam formed by the high-band beamforming array 160. In addition, implementing the ground wires 246-1 and 246-2 as corresponding frequency selective surfaces can change the electrical length of the ground wire 246 (for a fixed physical length), which can be used to make the ground wire 246 less resonant in the operating frequency band of the high-band beamforming array 160.

[0091] A frequency selective surface refers to a metallic structure designed to have a frequency selective response with respect to RF radiation incident thereon. For example, a frequency selective surface can be designed to partially or substantially transmit RF energy in a first frequency band while substantially reflecting RF energy in a second, different frequency band, thereby acting as a spatial filter. A frequency selective surface can include a plurality of periodically arranged unit cells, where each unit cell can be implemented in a single layer or in multiple fully overlapping metal layers. The unit cells can include inductive and / or capacitive structures that are coupled to each other or to the inductive and / or capacitive structures of adjacent unit cells such that the frequency selective surface is an LC resonant circuit. The LC resonant circuit can be designed to transmit more RF energy in a first frequency range than RF energy in a second frequency range. A general discussion of frequency selective surfaces can be found in Ben A. Munk, Frequency Selective Surfaces: Theory and Design, ISBN: 978-0-471-37047-5; DOI: 10.1002 / 0471723770; April 2000, All rights reserved. John Wiley & Sons, Inc., the contents of which are hereby incorporated by reference as if fully set forth herein.

[0092] Figure 3F FIG2 is a schematic perspective view of a small portion of one of the three unit cells 262 of the first feed handle printed circuit board 220-1 corresponding to a frequency selective surface for implementing one of the ground lines 246. As shown, the top metal layer 234-1 includes the signal line 242. The top metal layer 234-1 is not part of the frequency selective surface forming the ground line 246. The middle metal layer 234-2 includes a longitudinally extending metal trace 248 and a transversely extending metal trace 250 (only one of which is in FIG2). Figure 3F). The bottom metal layer 234-3 includes a metal pad 252. The signal line 242 may completely overlap with the middle longitudinally extending metal trace of the upper layer of the longitudinally extending metal traces 248 forming the double-layer ground line 246. The longitudinally extending metal traces 248 and the transversely extending metal traces 250 provided in each unit cell 260 form a cross-shaped metal pattern 262. The center of the cross-shaped metal pattern 262 of each unit cell 260 may overlap with the middle of the metal pad 252 of the corresponding unit cell 260. As shown in the figure, the cross-shaped metal pattern 262 of the upper layer of each unit cell 260 including the frequency selective surface ground line 246 is electrically connected to the cross-shaped metal pattern 262 of the adjacent unit cell 260 (and this occurs in both the longitudinal and transverse directions, even if the connection is only in the longitudinal direction). Figure 3F In contrast, the metal pads 252 of the lower layer of each unit cell 260, including the frequency selective surface ground line 246, are spaced apart from each other, so each metal pad 252 is capacitively edge-coupled only with the metal pad 252 of the adjacent unit cell 260. Each metal pad 252 is also capacitively coupled to a corresponding cross-shaped metal pattern 262 of the unit cell 260.

[0093] In some embodiments, the frequency selective surface may have a bandpass frequency response. In some embodiments, the frequency selective surface may have both a bandpass and a bandstop frequency response.

[0094] By implementing the first and second ground lines 246-1 and 246-2 as frequency selective surfaces, the negative impact of the feed handle 210 of the low-band radiating element 200 on the antenna beam generated by the high-band beamforming array 160 can be substantially reduced. Figure 1B As can be seen in the figure, the dual ground wires 30-1 and 30-2 provided on the feed stem of a conventional low-band radiating element comprise the vast majority of the metallization on the feed stem 10 and are a quarter-wavelength structure. Therefore, these ground wires 30 primarily serve to distort the antenna beam generated by the nearby high-band beamforming array 160. Because the low-band radiating element 200 according to an embodiment of the present invention includes a feed stem printed circuit board 220 having dual ground wires 246 that are partially transparent to RF energy within the high-band frequency range, the impact of the feed stem 210 on the high-band antenna beam can be significantly reduced. Furthermore, the electrical lengths of the first and second ground wires 246-1 and 246-2 can differ from the electrical lengths of the dual ground wires 30-1 and 30-2 included on each feed stem printed circuit board 20 of the conventional low-band radiating element 1, even though the physical lengths of the ground wires 30 and 246 can be the same. Therefore, the ground line 246 of the low-band radiating element 200 may be designed to not resonate in the operating frequency band of the high-band beamforming array 160 , which may also reduce or eliminate the second type of scattering.

[0095] Figure 4 yes Figures 3A-3F Graphs of the S1:1 and S1:2 transmission characteristics of the ground line of the low-band radiating element. Here, the beamforming array 160 is designed to operate in the 3.1-3.6 GHz frequency band. Figure 4 As shown in FIG, the frequency selective surface used to implement each ground line 246 passes at least -4 dB (40%) of incident RF energy in the 3.1-3.6 GHz frequency band, and passes up to -2.4 dB (58%) of incident RF energy in the middle of the 3.1-3.6 GHz frequency band. On average (i.e., averaged over 10 MHz intervals across the frequency band), these frequency selective surfaces pass approximately 50% of incident RF energy in the 3.1-3.6 GHz frequency band. Thus, the degree to which the ground lines on the feed stem of a radiating element according to embodiments of the present invention affect the high-band antenna beam can be significantly reduced.

[0096] As discussed above, by implementing the feed shank grounding wires as frequency selective surfaces, low-band radiating elements according to embodiments of the present invention can exhibit less scattering relative to the RF energy emitted by the high-band beamforming array 160. Furthermore, these frequency selective surface grounding wires can fully transmit low-band RF energy, thereby exhibiting, for example, return loss values below -45 dB for the entire low-band frequency range. Therefore, radiating elements according to embodiments of the present invention can improve the performance of the high-band beamforming array 160 without degrading the performance of the low-band array.

[0097] It should be understood that many modifications may be made to the radiating element discussed above without departing from the scope of the present invention. For example, the radiating element described above is formed using a feed stem printed circuit board. In other embodiments, other types of feed stem implementations may be used, such as a metal plate feed stem. As another example, the feed stem ground line may be implemented using a variety of different frequency selective surface designs, including, for example, single-layer and three-layer frequency selective surface designs and different frequency selective surfaces having unit cell structures different from the exemplary structure discussed above.

[0098] As another example, the signal traces on the feed stem can alternatively or additionally be implemented as frequency selective surfaces to reduce scattering caused by the metallization of the signal traces on the antenna beam generated by the high-band beamforming array. As yet another example, the same technique can be used on radiating elements operating in frequency bands other than the low band, such as on mid-band radiating elements.

[0099] Although the dipole arms of the low-frequency band radiating element described above are implemented on a dipole radiator printed circuit board, it should be understood that the embodiments of the present invention are not limited thereto. For example, in other embodiments, the dipole arms may be implemented as metal sheet dipole arms or may be implemented using other metal structures.

[0100] Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Throughout, like reference numerals represent like elements.

[0101] It will be understood that although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the present invention, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0102] It will be understood that when an element is described as being "on" another element, the element can be directly on the other element, or there can be an intermediate element. Conversely, when an element is described as being "directly on" another element, there are no intermediate elements. It will also be understood that when an element is described as being "connected" or "coupled" to another element, the element can be directly connected or coupled to the other element, or there can be an intermediate element. Conversely, when an element is described as being "directly connected" or "directly coupled" to another element, there are no intermediate elements. Other words used to describe the relationship between elements should be interpreted in a similar manner (i.e., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0103] Relative terms, such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer or region to another element, layer or region, as illustrated in the figures. It is to be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0104] In this context, the term "substantially" means within + / - 10%.

[0105] The terms used in this document are for the purpose of describing specific embodiments only and are not intended to limit 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 also be understood that the terms "including," "comprising," and / or "having," when used herein, refer to the presence of the recited 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 groupings thereof.

[0106] Aspects and elements of all of the embodiments disclosed above may be combined in any manner and / or with aspects or elements of other embodiments to provide multiple additional embodiments.

Claims

1. A radiating element, comprising: a feed handle having a signal line and a ground line, the ground line including a frequency selective surface; as well as A radiator is mounted on the feeding handle. The radiating element according to claim 1 , wherein the signal line overlaps with the ground line.

3. The radiating element of claim 1, wherein the frequency selective surface comprises at least two spaced-apart metal layers.

4. The radiating element of claim 1 , wherein the signal line and the ground line together comprise a radio frequency (“RF”) feed line configured to feed an RF signal to the radiator. The radiating element of claim 1 , wherein the frequency selective surface comprises a bandpass filter. 6 . The radiation element according to claim 1 , wherein the frequency selective surface comprises a plurality of unit cells, each unit cell comprising a first metal pattern and a second metal pattern positioned behind the first metal pattern. The radiation element of claim 6 , wherein the first metal pattern comprises a cross-shaped pattern. The radiation element of claim 7 , wherein the second metal pattern comprises a polygonal pad. 9 . The radiating element of claim 8 , wherein the first metal pattern of each unit cell is galvanically coupled to the first metal pattern of a corresponding adjacent unit cell. 10 . The radiating element of claim 9 , wherein the second metal pattern of each unit cell is capacitively edge-coupled to the second metal pattern of a corresponding adjacent unit cell.

11. A base station antenna, comprising: a first radiating element, the first radiating element being configured as the radiating element according to claim 1; as well as a second radiating element, the second radiating element being configured to operate in a higher operating frequency band than the first radiating element, The frequency selective surface comprises a bandpass filter having a passband that includes at least a portion of the higher operating frequency band.

12. The base station antenna of claim 12, wherein the first radiating element is mounted in front of the second radiating element.

13. A radiating element, comprising: Dipole radiator; as well as A feed handle printed circuit board having a first metal layer including a signal line configured to couple to a first conductor of a radio frequency ("RF") transmission line, a second metal layer configured to couple to a second conductor of the RF transmission line, and a third metal layer.

14. The radiating element of claim 13, wherein the feed stem printed circuit board further comprises a first dielectric substrate between the first metal layer and the second metal layer and a second dielectric substrate between the second metal layer and the third metal layer.

15. The radiating element of claim 14, wherein the second metal layer and the third metal layer together form a frequency selective surface.

16. The radiating element of claim 15, wherein the second metal layer comprises a ground line configured to be coupled to the second conductor of the RF transmission line. The radiating element of claim 16 , wherein the signal line and the ground line together comprise an RF feed line.

18. The radiating element of claim 15, wherein the frequency selective surface comprises a bandpass filter. 19 . The radiation element of claim 15 , wherein the frequency selective surface comprises a plurality of unit cells, each unit cell comprising a first metal pattern and a second metal pattern positioned behind the first metal pattern.

20. The radiating element of claim 19, wherein the first metal pattern comprises a cross-shaped pattern, and the second metal pattern comprises a polygonal pad.

21. The radiating element of claim 20, wherein the first metal pattern of each unit cell is galvanically coupled to the corresponding first metal pattern of the unit cell adjacent thereto, and the second metal pattern of each unit cell is capacitively edge coupled to the corresponding second metal pattern of the unit cell adjacent thereto.

22. A base station antenna, comprising: a first radiating element, the first radiating element being configured as the radiating element according to claim 15; as well as a second radiating element, the second radiating element being configured to operate in a higher operating frequency band than the first radiating element, The frequency selective surface comprises a bandpass filter having a passband that includes at least a portion of the higher operating frequency band.

23. A base station antenna, comprising: a first radiating element that is part of a first array of radiating elements, the first array of radiating elements being configured to operate in a first operating frequency band; as well as a second radiating element that is part of a second array of radiating elements, the second array of radiating elements being configured to operate in a second frequency band; The first radiation element comprises: a feed handle including a radio frequency ("RF") feed line; as well as A radiator connected to an RF feed transmission line, Wherein the feed handle includes a frequency selective surface configured to be at least 25% transparent on average to RF energy in the second frequency band.

24. The base station antenna of claim 23, wherein the RF feed line comprises a signal line and a ground line, and wherein at least a portion of the frequency selective surface forms the ground line.

25. The base station antenna of claim 24, wherein the frequency selective surface comprises a bandpass filter. 26 . The base station antenna of claim 25 , wherein the frequency selective surface comprises a plurality of unit cells, each unit cell comprising a first metal pattern and a second metal pattern positioned behind the first metal pattern.

27. The base station antenna of claim 26, wherein each first metal pattern comprises a corresponding cross-shaped pattern, and each second metal pattern comprises a corresponding polygonal pad.

28. The base station antenna of claim 24, wherein the frequency selective surface comprises a metal pattern including longitudinally extending metal traces and laterally extending metal traces, and wherein the signal line overlaps one of the longitudinally extending metal traces.

29. The base station antenna of claim 23, further comprising a second frequency selective surface, wherein the first radiating element is mounted in front of the second frequency selective surface, and the second radiating element is mounted behind the second frequency selective surface.

30. The radiating element of claim 11, wherein the frequency selective surface is configured to be at least 25% transparent on average to RF energy in the higher operating frequency band.

31. The radiating element of claim 11, wherein the frequency selective surface is configured to be at least 40% transparent on average to RF energy in the higher operating frequency band.

32. The radiating element of claim 1, wherein the ground line comprises a plurality of longitudinally extending traces and a plurality of transversely extending traces interconnected to form a grid.

33. The radiating element of claim 22, wherein the frequency selective surface is configured to be at least 25% transparent on average to RF energy in the higher operating frequency band.

34. The radiating element of claim 16, wherein the ground line comprises a plurality of longitudinally extending traces and a plurality of transversely extending traces interconnected to form a grid.

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