Lower band radiating element with reduced lower band radiation scattering

Abstract

The invention relates to a lower frequency band radiating element with reduced scattering of higher frequency band radiation. A radiating element includes: a feed stem printed circuit board including a first RF transmission line and a second RF transmission line; a first dipole radiator coupled to the first RF transmission line; and a second dipole radiator coupled to the second RF transmission line. The first dipole radiator comprises a first dipole arm and a second dipole arm, and the second dipole radiator comprises a third dipole arm and a fourth dipole arm. A first amount of coupling between the first dipole arm and the third dipole arm exceeds a second amount of coupling between the first dipole arm and the fourth dipole arm.

Description

Background Art

[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.

[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 fixed and mobile users within the cell served by the base station. Typically, the base station antenna is mounted on a tower or other elevated structure, with a radiation pattern (also referred to herein as an "antenna beam") generated by the base station antenna pointing outward.

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

[0004] Each of the above-mentioned linear arrays is coupled to two ports of a radio device (one port for each polarization). The RF signal transmitted by the linear array is passed from the radio device 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 (e.g., a sector of a cell). The relative phases of the subcomponents of the RF signal are set (e.g., using phase delay lines) so that the individual radiation patterns generated by each subset of the radiating elements constructively combine to reduce the half-power beamwidth ("HPBW") of the antenna beam generated in the elevation (vertical) plane. Because the above-mentioned 2G / 3G / 4G linear arrays generate static antenna beams, they 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 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 other frequency bands, such as the higher portion 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 dynamically adjust the amplitude and phase of the RF signal subcomponents fed to each column of the beamforming array 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 installed behind a passive base station antenna that includes multiple 2G, 3G and / or 4G passive linear arrays. An opening is provided in the reflector of the passive base station antenna so that the antenna beam generated by the active beamforming array can be transmitted through the passive base station antenna. Typically, some of the radiating elements of the 2G / 3G / 4G passive linear array are installed 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, a radiating element is provided, comprising: a feed stem printed circuit board including first and second RF transmission lines; a first dipole radiator coupled to the first RF transmission line; and a second dipole radiator coupled to the second RF transmission line. The first dipole radiator includes a first dipole arm and a second dipole arm, and the second dipole radiator includes a third dipole arm and a fourth dipole arm. A first coupling amount between the first dipole arm and the third dipole arm exceeds a second coupling amount between the first dipole arm and the fourth dipole arm.

[0008] In some embodiments, a third amount of coupling between the second dipole arm and the fourth dipole arm exceeds a fourth amount of coupling between the second dipole arm and the third dipole arm.

[0009] In some embodiments, the feed handle printed circuit board is positioned between the first dipole arm and the third dipole arm and between the second dipole arm and the fourth dipole arm.

[0010] In some embodiments, each of the first to fourth dipole arms is positioned adjacent to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front, wherein each of the first to fourth dipole arms has first and second inner sides, each extending outward from a center of the square, and first and second outer sides, each defining a respective portion of a perimeter of the square.

[0011] In some embodiments, each of the first through fourth dipole arms comprises a metal ring having an open interior.

[0012] In some embodiments, the difference between the first coupling amount and the second coupling amount is provided by a first capacitor disposed between a first inner distal end of the first dipole arm and a second inner distal end of the third dipole arm. In some embodiments, the difference between the third coupling amount and the fourth coupling amount is provided by a second capacitor disposed between a first inner distal end of the second dipole arm and a second inner distal end of the fourth dipole arm. In some embodiments, the first capacitor and the second capacitor are configured to improve isolation between the first dipole radiator and the second dipole radiator.

[0013] In some embodiments, the radiating element is provided in combination with a base station antenna, wherein the radiating element is one of a plurality of lower frequency band radiating elements. The base station antenna further comprises an array of higher frequency band radiating elements mounted behind the radiating element. In some embodiments, the radiating element further comprises a first metal stealth structure to a fourth metal stealth structure overlapping the corresponding first dipole arm to the fourth dipole arm, wherein the first metal stealth structure to the fourth metal stealth structure are configured to make the corresponding first dipole arm to the fourth dipole arm substantially transparent to the RF radiation emitted by the higher frequency band radiating element. In some embodiments, the first dipole arm to the fourth dipole arm and the first metal stealth structure to the fourth metal stealth structure are formed on a dielectric substrate of a dipole radiator printed circuit board. In some embodiments, the array of higher frequency band radiating elements comprises a plurality of columns of higher frequency band radiating elements, wherein the columns extend in the longitudinal direction of the base station antenna, and wherein the first major surface and the second major surface of the feed handle printed circuit board extend forward from the reflector of the base station antenna and perpendicular to the longitudinal direction. In some embodiments, the first to fourth dipole arms are installed adjacent to a front end of the feeding handle, and the first to fourth metal stealth structures are installed behind the corresponding first to fourth dipole arms.

[0014] In some embodiments, the metal ring of the first dipole arm can include a slot that omits the metal. In such embodiments, the slot can include a first slot segment and a second slot segment that intersect to define a right angle. The slot can be positioned adjacent to an outer corner of the first dipole arm. In some embodiments, the length of the slot can be a quarter wavelength of a frequency within the operating band of a higher-band radiating element also included in the base station antenna.

[0015] In some embodiments, the radiating element may further include first to fourth metal traces positioned radially outward of the respective first to fourth dipole arms and configured to capacitively couple with the respective first to fourth dipole arms. Each of the first to fourth metal traces may, for example, have a right-angle shape. The length of each of the first to fourth metal traces may be a quarter wavelength of a frequency within the operating band of the higher-band radiating element.

[0016] According to another embodiment of the present invention, a radiating element is provided, comprising: a feed stem printed circuit board, the feed stem printed circuit board including first and second RF transmission lines; a first dipole radiator coupled to the first RF transmission line; and a second dipole radiator coupled to the second RF transmission line. The first dipole radiator includes a first dipole arm and a second dipole arm, and the second dipole radiator includes a third dipole arm and a fourth dipole arm. The feed stem printed circuit board is positioned between the first and third dipole arms and between the second and fourth dipole arms, and the inward-facing distal ends of the first and third dipole arms are spaced closer together than the inward-facing distal ends of the first and fourth dipole arms.

[0017] In some embodiments, the inward-facing distal ends of the second and fourth dipole arms are more closely spaced apart than the inward-facing distal ends of the second and third dipole arms.

[0018] In some embodiments, the first and third dipole arms are symmetrically oriented inwardly about a first axis, and the first and fourth dipole arms are symmetrically oriented inwardly about a second axis. In some embodiments, the second and fourth dipole arms are symmetrically oriented inwardly about the first axis, and the second and third dipole arms are symmetrically oriented inwardly about the second axis. In some embodiments, the feed handle printed circuit board extends along the first axis.

[0019] In some embodiments, each of the first to fourth dipole arms is positioned next to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front.

[0020] In some embodiments, each of the first through fourth dipole arms comprises a metal ring having an open interior.

[0021] In some embodiments, the first RF transmission line is coupled to the first dipole radiator, and the second RF transmission line is coupled to the second dipole radiator.

[0022] In some embodiments, the radiating element is provided in combination with a base station antenna, wherein the radiating element is one of a plurality of lower frequency band radiating elements. The base station antenna may include an array of higher frequency band radiating elements mounted behind the radiating element. The radiating element may also include a first metal stealth structure to a fourth metal stealth structure overlapping with the corresponding first dipole arm to the fourth dipole arm, wherein the first metal stealth structure to the fourth metal stealth structure are configured to make the corresponding first dipole arm to the fourth dipole arm substantially transparent to the RF radiation emitted by the higher frequency band radiating element. In some embodiments, the array of higher frequency band radiating elements includes a plurality of columns of arrays of higher frequency band radiating elements, wherein the columns extend in the longitudinal direction of the base station antenna, and the first major surface and the second major surface of the feed handle printed circuit board extend forward from the reflector of the base station antenna and perpendicular to the longitudinal direction.

[0023] In some embodiments, the first to fourth dipole arms and the first to fourth metal stealth structures are formed on a dielectric substrate of a dipole radiator printed circuit board.

[0024] In some embodiments, the first to fourth dipole arms are installed adjacent to a front end of the feeding handle, and the first to fourth metal stealth structures are installed behind the corresponding first to fourth dipole arms.

[0025] According to yet other embodiments of the present invention, a radiating element is provided, comprising a first dipole radiator and a second dipole radiator, wherein the first dipole radiator comprises a first dipole arm and a second dipole arm, and the second dipole radiator comprises a third dipole arm and a fourth dipole arm.

[0026] The first dipole radiator is configured to transmit and receive electromagnetic radiation within a first operating frequency band, and the second dipole radiator is configured to transmit and receive electromagnetic radiation within the first operating frequency band. The radiating element further includes first to fourth metal stealth structures, which form a resonant circuit with the corresponding first to fourth dipole arms. The resonant circuit is configured to allow current in the first operating frequency band to flow through the first to fourth dipole arms, while preventing current in the second operating frequency band from flowing through the first to fourth dipole arms. A first coupling amount between the first dipole arm and the third dipole arm exceeds a second coupling amount between the first dipole arm and the fourth dipole arm.

[0027] In some embodiments, a third amount of coupling between the second dipole arm and the fourth dipole arm exceeds a fourth amount of coupling between the second dipole arm and the third dipole arm.

[0028] In some embodiments, each of the first to fourth metal stealth structures and corresponding dipole arms from the first to fourth dipole arms form a multi-stage resonant circuit. In some embodiments, each multi-stage resonant circuit includes a plurality of resonant circuits connected in series with each other.

[0029] In some embodiments, each of the first through fourth dipole arms comprises a loop-shaped dipole arm.

[0030] In some embodiments, the radiating element further comprises a feed stem printed circuit board comprising first and second RF transmission lines coupled to respective first and second dipole radiators. In some embodiments, the feed stem printed circuit board is positioned between the first and third dipole arms and between the second and fourth dipole arms.

[0031] In some embodiments, each of the first to fourth dipole arms is positioned adjacent to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front, and wherein each of the first to fourth dipole arms comprises a metal ring having an open interior.

[0032] In some embodiments, the difference between the first coupling amount and the second coupling amount is provided by a first capacitor disposed between a first inner distal end of the first dipole arm and a second inner distal end of the third dipole arm. In some embodiments, the difference between the third coupling amount and the fourth coupling amount is provided by a second capacitor disposed between a first inner distal end of the second dipole arm and a second inner distal end of the fourth dipole arm. In some embodiments, the first capacitor and the second capacitor are configured to improve isolation between the first dipole radiator and the second dipole radiator.

[0033] According to yet another additional embodiment of the present invention, a radiating element is provided, comprising a first dipole radiator and a second dipole radiator, wherein the first dipole radiator comprises a first dipole arm and a second dipole arm, and the second dipole radiator comprises a third dipole arm and a fourth dipole arm. Each of the first to fourth dipole arms comprises a first metal dipole arm segment and a second metal dipole arm segment having a plurality of slots in which metal is omitted, the slots being configured to increase the length of a corresponding current path along each of the first and second metal dipole arm segments.

[0034] In some embodiments, the first metallic dipole arm segment and the second metallic dipole arm segment of each of the first to fourth dipole arms together form respective first to fourth metallic rings having an open interior.

[0035] In some embodiments, for each of the first to fourth dipole arms, some of the slots are outwardly extending slots extending outward from the interior of the corresponding one of the first to fourth metal rings, while other of the slots are inwardly extending slots extending inward from the exterior of the corresponding one of the first to fourth metal rings.

[0036] In some embodiments, for each of the first to fourth dipole arms, at least two (or three) outwardly extending slots and at least two (or three) inwardly extending slots are arranged in an alternating manner.

[0037] In some embodiments, each of the first to fourth metal rings generally defines a respective annular square, and wherein a majority of the slots in each side of each of the annular squares extend perpendicular to a longitudinal direction of the side of the respective annular square.

[0038] In some embodiments, the radiating element further comprises a feed stem having a base and a distal end, wherein the first dipole radiator and the second dipole radiator are mounted adjacent the distal end of the feed stem.

[0039] In some embodiments, the slots have equal widths.

[0040] In some embodiments, the outside of each annular square has a substantially constant width.

[0041] In some embodiments, the radiation element further includes first to fourth metal stealth structures overlapping with the corresponding first to fourth dipole arms.

[0042] According to another embodiment of the present invention, a radiating element is provided, comprising a first dipole radiator and a second dipole radiator, wherein the first dipole radiator comprises a first dipole arm and a second dipole arm, and the second dipole radiator comprises a third dipole arm and a fourth dipole arm. Each of the first to fourth dipole arms comprises a metal ring having an open interior, wherein the metal ring has a corresponding slot provided therein, wherein the metal in the metal ring of each of the first to fourth dipole arms is omitted.

[0043] In some embodiments, each slot can include a first slot segment and a second slot segment that intersect to define a corresponding right angle. In some embodiments, each slot is positioned adjacent to an outer corner of each of the corresponding first to fourth dipole arms. In some embodiments, the radiating element can also include first to fourth metal traces positioned radially outward of the corresponding first to fourth dipole arms and configured to capacitively couple with the corresponding first to fourth dipole arms. In such embodiments, each of the first to fourth metal traces can have a right-angle shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1A is a schematic perspective view of a passive / active antenna system including a passive base station antenna, which may be implemented using a mid-band radiating element, according to an embodiment of the present invention.

[0045] Figure 1B yes Figure 1A Schematic front view of a passive / active antenna system without the frequency selective surface and radome.

[0046] Figure 2A is a schematic perspective view of a mid-band crossed-dipole radiating element according to an embodiment of the present invention.

[0047] Figure 2B yes Figure 2A Schematic top view of the printed circuit board feeding shank of a mid-band crossed-dipole radiating element.

[0048] Figure 2C yes Figure 2B Schematic bottom view of the feed handle printed circuit board.

[0049] Figure 2D yes Figure 2B Schematic top view shadow diagram of the feed handle printed circuit board.

[0050] Figure 2E yes Figure 2A Schematic front-shaded diagram of a mid-band crossed-dipole radiating element.

[0051] Figure 2F yes Figure 2A Schematic back-shaded diagram of a mid-band crossed-dipole radiating element.

[0052] Figure 3A yes Figure 2A Schematic front view of a modified version of a mid-band crossed dipole radiating element.

[0053] Figure 3B It is a comparison Figure 2A and Figure 3A A graph of the cross-polarization isolation performance of the radiating elements.

[0054] Figure 4 is a schematic front shadow diagram of a mid-band radiating element according to another embodiment of the present invention.

[0055] Figures 5A-5C is a schematic front shadow view of a dipole radiator printed circuit board of a mid-band radiating element according to an additional embodiment of the present invention.

[0056] Figure 6A and Figure 6B is a schematic front perspective shadow diagram of a mid-band radiating element according to yet another additional embodiment of the present invention.

[0057] Figure 7A is a schematic front shadow diagram of a mid-band radiating element according to yet other embodiments of the present invention.

[0058] Figures 7B to 7D is a graph showing the current distribution on the radiating element in response to different types of higher frequency band radiation Figure 7A An enlarged schematic front-shaded view of a corner of a mid-band radiating element.

[0059] Several of the accompanying drawings are "shadow" diagrams of a printed circuit board included in a radiating element according to an embodiment of the present invention. In these shadow diagrams, the dielectric substrate of the printed circuit board is drawn transparent to illustrate portions of the metallization pattern on the far side of the printed circuit board that are not covered by the metallization pattern on the near side of the printed circuit board. DETAILED DESCRIPTION

[0060] The passive / active antenna systems described above allow cellular operators to use a single base station antenna to support both legacy 2G / 3G / 4G cellular services and 5G cellular services. Unfortunately, in practice, the radiating elements of the passive 2G / 3G / 4G arrays mounted in front of the 5G beamforming arrays can cause "scattering" of the RF radiation generated by the 5G beamforming arrays. 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.

[0061] Two different types of scattering can occur. First, the conductive structures of the radiating elements of the lower frequency (passive) linear 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.

[0062] The second type of scattering occurs when the conductive structures of the radiating elements of the passive 2G / 3G / 4G linear array have an electrical length that causes the structures to resonate in the operating frequency band of the 5G beamforming array. For example, the conductive structures of the radiating elements of one of the passive (lower-band) arrays may resonate in the operating frequency band of the 5G (higher-band) beamforming array if the electrical length of the conductive structures 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 twice the frequency within the operating frequency band of the passive mid-band linear array. For example, because the dipole arms of the radiating elements of the high-band linear array typically have an electrical length of approximately 1 / 4 of the center wavelength of the mid-band operating frequency range, they may have a resonant length with respect to the RF energy transmitted by the 5G beamforming array. Thus, the RF energy emitted by the 5G beamforming array can couple to, for example, the dipole arms of a nearby mid-band radiating element, and the higher-band currents developed on these dipole arms produce additional high-band radiation that distorts the high-band antenna beam (because some of the RF energy is emitted from unintended locations, i.e., from the mid-band dipole arms).

[0063] One approach to preventing the mid-band radiating elements from distorting the antenna beam generated by the high-band beamforming array is to position the mid-band linear array in one portion of the passive / active antenna system (e.g., the lower portion) and the high-band beamforming array in a different portion of the passive / active antenna system (e.g., the upper portion). However, because cellular operators typically have strict restrictions on the acceptable lengths of different types of base station antennas, spatially offsetting the mid-band linear array from the high-band beamforming array typically imposes restrictions on the length of the mid-band linear array. Since the gain of a linear array varies with the length of the array, this approach can limit the maximum gain of the mid-band linear array (and / or the high-band beamforming array).

[0064] To increase the gain of the mid-band linear array, the length of some or all of the mid-band linear arrays can be increased so that the mid-band radiating elements are mounted beside and / or in front of the high-band beamforming array. However, when the high-band antenna beam is scanned in the direction of the mid-band radiating elements, the mid-band radiating elements mounted in front of the high-band beamforming array can cause the two types of scattering described above, and the mid-band radiating elements mounted beside the high-band beamforming array can also cause both types of scattering. Therefore, while increasing the length of the mid-band linear array can improve its gain, the longer mid-band linear array can cause scattering of the high-band antenna beam, which can reduce the gain, beamwidth, and beam shape of the high-band antenna beam.

[0065] So-called "stealth" or "cloaked" radiating elements having dipole arms designed so that current will largely not form therein in response to RF radiation within a preselected frequency range (e.g., the operating frequency band of high-band radiating elements in 5G beamforming arrays) are known in the art. These radiating elements can reduce the second type of scattering discussed above, but generally do not reduce the first type of scattering.

[0066] According to an embodiment of the present invention, a mid-band radiating element is provided, which can reduce the impact on the antenna beam of a high-band beamforming array. The mid-band radiating element according to an embodiment of the present invention can have a dipole radiator, which is invisible relative to the RF radiation in the operating frequency band of the high-band beamforming array. This can significantly reduce the degree of high-band current formed on the mid-band dipole arm, thereby suppressing the high-band RF radiation scattering of the first type discussed above. In addition, the mid-band radiating element according to an embodiment of the present invention may include a single feed handle printed circuit board positioned parallel to the scanning direction of the high-band beamforming array. This can significantly reduce the degree of reflection of high-band RF radiation by the feed handle of the mid-band radiating element, thereby suppressing the high-band RF radiation scattering of the second type discussed above. The mid-band radiating element also can not include any director, which further reduces the scattering of high-band radiation. Through these technologies, the mid-band radiating element according to an embodiment of the present invention can only have a small impact on the high-band antenna beam (for example, the directivity is reduced by about 0.1dB on average).

[0067] Unfortunately, when a dual-polarized radiating element includes a single feed shank printed circuit board that includes RF transmission lines for each polarization, an imbalance may occur that may reduce the cross-polarization isolation of the dual-polarized radiating element. To counteract this imbalance, the dipole arms of a mid-band radiating element according to embodiments of the present invention can have asymmetric coupling with adjacent dipole arms, where the asymmetric coupling is designed to compensate for the imbalance. Thus, a radiating element according to embodiments of the present invention can include only a single feed shank printed circuit board while still exhibiting a high degree of cross-polarization isolation. The dipole arms can offset the imbalance in the feed shank by, for example, positioning the inner distal ends of selected dipole arms to exhibit increased coupling.

[0068] A radiating element according to an embodiment of the present invention may include first to fourth dipole arms and first to fourth metal stealth structures, wherein the first to fourth metal stealth structures are mounted to overlap with the corresponding first to fourth dipole arms. Each metal stealth structure can be capacitively coupled to a corresponding dipole arm in the dipole arms and can form one or more resonant circuits with the dipole arm. These resonant circuits can be configured to make the dipole arms invisible relative to RF radiation in the operating frequency bands of different arrays of radiating elements included in a base station antenna including a radiating element according to an embodiment of the present invention. The radiating element may include coupling (e.g., capacitive or inductive coupling) between selected dipole arms in the dipole arms that offsets imbalances in the feed handle.

[0069] According to another embodiment of the present invention, a cross-dipole radiating element is provided, in which the dipole arms are implemented as metal rings. A plurality of outwardly extending slots are provided in the inner side of the conductive ring, and a plurality of inwardly extending slots are provided in the outer side of the metal ring. The inwardly extending slots and the outwardly extending slots may be alternated so that each outwardly extending slot may be adjacent to at least one, typically two inwardly extending slots, and so that each inwardly extending slot may be adjacent to at least one, typically two outwardly extending slots. These slots may significantly increase the length of the current path along each dipole arm, which allows reducing the overall size of the dipole arm (i.e., the length of the periphery of the dipole arm when viewed from the front) while still maintaining an electrical length suitable for working as a mid-band radiating element. The reduced size of these radiating elements may further reduce the impact of the mid-band radiating element according to an embodiment of the present invention on the radiation pattern of a nearby high-band radiating element.

[0070] According to a further embodiment of the present invention, there is provided a base station antenna comprising one or more linear arrays of the above-mentioned mid-band radiating elements.The base station antenna may be a passive base station antenna, for example, of a passive / active antenna system.

[0071] Before discussing radiating elements according to embodiments of the present invention, it is helpful to discuss the design and operation of an exemplary base station antenna in which radiating elements according to embodiments of the present invention may be used.

[0072] Figures 1A-1B A conventional base station antenna is shown in the form of a passive / active antenna system 1 comprising both a passive base station antenna 10 and an active antenna module 50. In particular, Figure 1A is a schematic rear perspective view of the passive / active antenna system 1, and Figure 1B The frequency selective surface and the radome of both the passive base station antenna 10 and the active antenna module 50 are omitted. Figure 1A A schematic perspective view of a passive / active antenna system 1 is shown. Figure 1A and Figure 1B , the axes show the longitudinal (L), transverse (T) and forward (F) directions of the passive / active antenna system 1. In the following description, the passive / active antenna system 1 and the radiating elements included therein will be described using terms normally used assuming that the passive / active antenna system 1 is mounted on a tower, wherein the longitudinal axis of the passive / active antenna system 1 extends along the vertical axis and the front surface of the passive / active antenna system 1 is mounted opposite the tower so as to point towards the coverage area of ​​the antenna 1.

[0073] refer to Figure 1AThe passive / active antenna system 1 can be mounted, for example, on an antenna tower 2 using mounting hardware 4. The active antenna module 50 can be mounted directly on the rear surface of the passive base station antenna 10, or can be held in place behind the passive base station antenna 10 by the mounting hardware 4. The front surface of the passive / active antenna system 1 can face the antenna tower 2, facing the coverage area of ​​the passive / active antenna system 1. The passive base station antenna 10 includes a tubular radome 12 that surrounds and protects the antenna assembly mounted inside the radome 12. A top end cap 14 covers the top opening in the radome 12, and a bottom end cap 16 covers the bottom opening in the radome 12. A plurality of RF ports 18 extend through the bottom end cap 16 and are used to connect the passive base station antenna 10 to one or more external radio devices (not shown). The active antenna module 50 can be removably mounted behind the passive base station antenna 10, so that the active antenna module 50 can be later replaced with a different active antenna module.

[0074] refer to Figure 1B The passive base station antenna 10 includes a reflector assembly 20. The reflector assembly 20 may be referred to herein as a "passive reflector assembly" because it is part of the passive base station antenna 10. The passive reflector assembly 20 includes a main reflector 22 and first and second spaced-apart reflector strips 24-1 and 24-2, each extending longitudinally from first and second opposing sides of the main reflector 22. It should be noted that herein, like elements may be referred to individually by their full reference numerals (e.g., reflector strip 24-1) and collectively by the first portion of their reference numerals (e.g., reflector strip 24). The passive reflector assembly 20 may also include a third reflector strip 24-3 extending in a transverse direction between the top ends of the first and second reflector strips 24-1 and 24-2. An opening 26 is defined between the first and second reflector strips 24-1 and 24-2. For example, the opening 26 can be defined by the top portion of the main reflector 22, the first and second reflector strips 24-1, 24-2, and the third reflector strip 24-3. At least the main reflector 22 can include or contain a metal surface (e.g., an aluminum sheet) that acts as a reflector and a ground plane for the radiating elements of the antenna 1. Various mechanical and electronic components of the antenna (not shown) can be mounted behind the passive reflector assembly 20, such as phase shifters, remote electronic tilt units, mechanical linkages, controllers, duplexers, etc. To illustrate the components mounted behind the frequency selective surface 28, the following diagram is provided: Figure 1B The frequency selective surface 28 is not shown. Figure 1B The dashed box (labeled 28) provided in FIG. 1 shows the location where the frequency selective surface 28 is mounted.

[0075] A frequency selective surface 28 is provided that overlaps and / or covers the opening 26. A frequency selective surface is a conductive (typically metallic) structure that is designed to have a frequency selective response with respect to RF radiation incident thereon. For example, the frequency selective surface can be designed to partially or substantially pass RF energy in a first frequency band while substantially reflecting RF energy in a second, different frequency band, thereby acting as a spatial filter. The frequency selective surface 28 can be coplanar with the opening 26 or mounted in front of or behind the opening 26. In some cases, the opening 26 can be omitted and a large number of small openings can be punched into the main reflective surface 22 (in the place of the opening 26) to form the frequency selective surface 28 in the main reflective surface 22.

[0076] The frequency selective surface 28 can be configured to allow RF energy emitted by the radiating elements of the high-band beamforming array (discussed below) included in the active antenna module 50 to pass through it, while at the same time reflecting RF energy in the operating bands of the low-band radiating elements and mid-band radiating elements (discussed below) included in the passive base station antenna 10. The frequency selective surface 28 can have a grid pattern, such as a grid of metal patches and / or other metal structures forming a plurality of periodically arranged unit cells. 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 28. The grid pattern can include sub-wavelength periodic microstructures. The unit cells can include inductive and / or capacitive structures that couple to each other or to the inductive and / or capacitive structures of adjacent unit cells, such that the frequency selective surface 28 forms an LC resonant circuit. The LC resonant circuit can be designed to be more transparent to RF energy within a first frequency range than to RF energy within 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.

[0077] The passive base station antenna 10 also includes a plurality of passive linear arrays of radiating elements extending forward from the passive reflector assembly 20. The linear arrays may support, for example, 2G, 3G and / or 4G cellular services. Figures 1A-1BIn the exemplary passive base station antenna 10 shown in FIG, the linear arrays include a first low-band linear array and a second low-band linear array 30-1, 30-2 configured to operate in all or part of the 617-960 MHz frequency band. Each low-band linear array 30 includes a vertically extending column of low-band radiating elements 32. The passive base station antenna 10 also includes a first mid-band linear array 40-1 to a fourth mid-band linear array 40-4 configured to operate in all or part of the 1427-2690 MHz frequency band. Each mid-band linear array 40 includes a vertically extending column of mid-band radiating elements 42. Each of the low-band linear array and the mid-band linear array 30, 40 can generate a relatively static antenna beam (e.g., an antenna beam each configured to cover a sector of a base station) that provides 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).

[0078] Each of the low-band radiating elements and the mid-band radiating elements 32, 42 can be implemented as a dual-polarization radiating element, comprising a first radiator and a second radiator that transmits and receives RF energy with orthogonal polarizations. When such dual-polarization radiating elements are used, each of the low-band linear array and the mid-band linear array 30, 40 can be connected to a pair of RF ports 18. The first RF port 18 is connected between a first port of a radio device (e.g., a remote radio head) and a first polarization radiator of a radiating element in a linear array, and the second RF port 18 is connected between a second port of the radio device and a second polarization radiator of a radiating element in the linear array. The RF signal transmitted by a selected one of the linear arrays 30, 40 is passed from the radio device to one of the RF ports 18, and from the RF port 18 to a power splitter (or, alternatively, a phase shifter assembly including a power splitter), which splits the RF signal into a plurality of sub-components, which are fed to corresponding first or second radiators of the radiating elements in the linear array, where the sub-components of the RF signal are radiated into free space.

[0079] The low-band radiating elements and / or mid-band radiating elements 32, 42 may be mounted on a feeder printed circuit board that couples RF signals to and from the respective radiating elements 32, 42. Figure 1B In the figure, mid-band radiating elements 42 are shown mounted in pairs on a plurality of mid-band feed board printed circuit boards 44. (Low-band radiating elements are also mounted on the feed board printed circuit boards, but are not visible in the figure.) Cables can be used to connect each feed board printed circuit board 44 to other components of the antenna, such as a duplexer, phase shifters, etc.

[0080] Most of the low-band radiating elements and mid-band radiating elements 32, 42 are mounted to extend forward from the main reflector 22. However, the low-band linear arrays 30-1, 30-2 extend substantially the full length of the passive / active antenna system 1 and, therefore, extend beyond (above) the main reflector 22. The first and second reflector strips 24-1, 24-2 provide mounting locations for the low-band radiating elements 32 positioned above the main reflector 22. The first and second reflector strips 24-1, 24-2 can be integral with the main reflector 22 so that the first and second reflector strips 24-1, 24-2 and the main reflector 22 are maintained at a common ground voltage, which can improve the performance of the low-band linear arrays 30-1, 30-2. Similarly, the mid-band linear arrays 40 - 1 , 40 - 4 extend beyond (above) the main reflector 22 , with the first and second reflector strips 24 - 1 , 24 - 2 also providing mounting locations for the mid-band radiating elements 42 positioned above the main reflector 22 .

[0081] Each low-band radiating element 32 and mid-band radiating element 42 may include a tilted -45° / +45° cross-dipole radiating element, the cross-dipole radiating element including a tilted -45° polarized dipole radiator and a tilted +45° polarized dipole radiator. The dipole radiator may be mounted on a feed handle (not visible). In antenna 1, the low-band radiating element and mid-band radiating elements 32, 42 mounted above the main reflector 22 are mounted on reflector strips 24-1, 24-2. It should be understood that in other passive / active antenna systems, the low-band radiating element 32 and / or the mid-band radiating element 42 may be mounted on the frequency selective surface 28 instead.

[0082] The active antenna module 50 includes a multi-column beamforming array 60 of radiating elements 62 and a beamforming radio (not visible in the figure). The multi-column beamforming array 60 can be mounted in the front portion of the active antenna module 50 behind the frequency selective surface 28. The beamforming radio can be mounted behind the multi-column beamforming array 60. The beamforming array 60 can, for example, include multiple vertically extending columns of high-band radiating elements 62 configured to operate in all or part of the 3.1-4.2 GHz frequency band (e.g., in the 3.4-4.0 GHz frequency band). The high-band radiating elements 62 are mounted to extend forward from the reflector 54 (herein referred to as the "active reflector") of the active antenna module 50. The beamforming radio can electronically adjust the amplitude and / or phase of subcomponents of the RF signal output to different radiating elements 62 of the multi-column beamforming array 60. For example, each port of a beamforming radio may be coupled to a column of radiating elements of the beamforming array 60, 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.

[0083] As described above, the beamforming array 60 of active antenna modules 50 is mounted behind the frequency selective surface 28. The beamforming array 60 is Figure 1B It can be seen in Figure 1B The frequency selective surface 28 and the radome of the passive base station antenna 10 are omitted, as is the radome of the active antenna module 50. The opening 26 in the passive reflector assembly 20 and the frequency selective surface 28 allow the antenna beam generated by the beamforming array 60 to pass through the reflector assembly 20 to provide service to the coverage area of ​​the passive / active antenna system 1. The frequency selective surface 28 acts as a reflector for RF radiation in the low-band and mid-band frequency ranges.

[0084] Figures 1A-1B One difficulty with the passive / active antenna system 1 is that the top four mid-band radiating elements 42 in the mid-band linear arrays 40-1 and 40-4 are mounted on the respective reflector strips 24-1, 24-2. Therefore, when the antenna beam generated by the high-band beamforming array 60 is scanned in the azimuth plane, a large amount of high-band RF radiation can be incident on these mid-band radiating elements 42. Furthermore, in some cases, the mid-band linear arrays 40-2, 40-3 can be lengthened so that some of the mid-band radiating elements 42 in these mid-band linear arrays 40-2, 40-3 are mounted directly in front of the high-band beamforming array 60 (e.g., mounted on the frequency selective surface 28). As a result, the mid-band linear arrays 40-1 through 40-4 can distort the antenna beam generated by the high-band beamforming array 60.

[0085] Figures 2A-2F A mid-band crossed-dipole radiating element 100 according to an embodiment of the present invention is shown. In particular, Figure 2A is a schematic perspective view of a mid-band crossed dipole radiating element 100, and Figure 2B and Figure 2C are schematic front and rear views of the feed shank printed circuit board of the mid-band radiating element 100, and Figure 2D is a schematic front shadow diagram of the feed handle printed circuit board. Finally, Figure 2E and Figure 2F are schematic front and rear shadow diagrams of the mid-band radiating element 100. Figure 2D , the solid lines illustrate the metallization pattern on a first side of the feed stem printed circuit board, and the dashed lines illustrate the metallization pattern on a second (opposite) side of the feed stem printed circuit board. The mid-band crossed-dipole radiating element 100 can, for example, be used to implement at least some of the mid-band radiating elements 42 included in the passive / active antenna system 1.

[0086] like Figure 2A As shown in FIG, a mid-band crossed-dipole radiating element 100 includes a feed stem 110 and a dipole radiator printed circuit board 140 having first and second dipole radiators 152-1 and 152-2 formed therein. The dipole radiator printed circuit board 140 is mounted adjacent to (and typically mounted on) the distal end of the feed stem 110. The mid-band crossed-dipole radiating element 100 does not include any directors.

[0087] refer to Figures 2A-2D The feed stem 110 includes a single feed stem printed circuit board 110 including a dielectric substrate 112 having first and second metallization patterns 120 and 130 formed on both major surfaces thereof. First and second RF transmission lines 114-1 and 114-2 are formed in the feed stem printed circuit board 110. These RF transmission lines 114-1 and 114-2 transmit RF signals between first and second RF transmission lines (not shown) of a feed network and corresponding dipole radiators 152-1 and 152-2.

[0088] like Figure 2B As shown in FIG, the first metallization pattern 120 mainly includes a pair of ground lines 122-1, 122-2 forming a dual ground line structure of the first RF transmission line 114-1 and a hook-shaped balun 124 including a signal trace of the second RF transmission line 114-2. Figure 2CAs shown in FIG, the second metallization pattern 130 mainly includes a pair of ground lines 132-1, 132-2 forming a dual ground line structure of the second RF transmission line 114-2 and a hook-shaped balun 134 including a signal trace of the first RF transmission line 114-1.

[0089] The rear end (base) of each ground line 122-1, 122-2 is coupled to a ground conductor of a first RF transmission line (not shown) of the feed network for radiating element 100. The rear end of signal trace 134 is coupled to a signal conductor of the first RF transmission line of the feed network for radiating element 100. Similarly, the rear end of each ground line 132-1, 132-2 is coupled to a ground conductor of a second RF transmission line (not shown) of the feed network for radiating element 100, and the rear end of signal trace 124 is coupled to a signal conductor of the second RF transmission line of the feed network for radiating element 100. Each ground line 122, 132 may each have an electrical length of approximately ¼ of the wavelength corresponding to the center frequency of the operating frequency band of radiating element 100. As further shown, a first plated through hole 116-1 extending through the dielectric substrate 112 is provided that allows the front end of the ground wire 122-2 to transition to the opposite side of the dielectric substrate 112 (to become part of the metallization pattern 130), so that the ground wire 122-2 is in a suitable position to be soldered to one of the dipole arms of the dipole radiator 152-1 (discussed below). Similarly, a plated through hole 116-2 extending through the dielectric substrate 112 is provided that allows the front end of the ground wire 132-2 to transition to the opposite side of the dielectric substrate 112 (to become part of the metallization pattern 120), so that the ground wire 132-2 is in a suitable position to be soldered to one of the dipole arms of the dipole radiator 152-2 (discussed below).

[0090] refer to Figure 2E and Figure 2F The dipole radiator printed circuit board 140 includes a dielectric substrate 142 having first and second metallization layers 150, 160 formed on both major surfaces thereof. In the depicted embodiment, the dielectric substrate 142 has a square shape. A first dipole radiator 152-1 extends along a first axis (-45° axis), and a second dipole radiator 152-2 extends along a second axis (+45°) that is substantially perpendicular to the first axis. The first dipole radiator 152-1 includes first and second dipole arms 154-1, 154-2, and the second dipole radiator 152-2 includes third and fourth dipole arms 154-3, 154-4.

[0091] The dipole arms 154-1 and 154-2 of the first dipole radiator 152-1 are centrally fed by the first RF feed line 114-1 and radiate together with a first polarization, which is here a tilted -45° linear polarization. The dipole arms 154-3 and 154-4 of the second dipole radiator 152-2 are centrally fed by the second RF feed line 114-2 and radiate together with a second polarization orthogonal to the first polarization, which is here a tilted +45° linear polarization.

[0092] like Figure 2E As best shown in FIG. , each dipole arm 154 is formed as a generally square, annular conductive ring. The first and second dipole radiators 152-1, 152-2 are arranged crosswise relative to one another, such that the four dipole arms 154 are positioned in four quadrants of a square 157 defined by the dielectric substrate 142. Thus, each dipole arm 154 includes two "inner" sides 156-1, 156-2 extending from the center of the dipole radiator printed circuit board 140 to two different edges thereof, and two "outer" sides 158-1, 158-2 extending along respective edges of the square 157 defined by the dipole arms 154. Portions of the inner sides 156-1, 156-2 of each dipole arm 154 are widened compared to the majority of each dipole arm 154. Widening these portions of the dipole arms 154 can improve impedance matching between the dipole arms 154 and the RF transmission line 114 on the feed handle printed circuit board 110.

[0093] The dipole radiator printed circuit board 140 includes an opening therethrough in the form of a slot 144. The front end of the feed stem printed circuit board 110 can extend through the slot 144. Because only a single feed stem printed circuit board 110 is provided, the interface between the feed stem printed circuit board 110 and the dipole radiator printed circuit board 140 may be unbalanced. As shown, the feed stem printed circuit board 110 is positioned between the first dipole arm 154-1 and the third dipole arm 154-3, and between the second dipole arm 154-2 and the fourth dipole arm 154-4. It has been found that the imbalance introduced by the single feed stem printed circuit board 110 may reduce the isolation between the dipole radiators 152-1 and 152-2 (i.e., the unbalanced design may reduce the cross-polarization isolation of the radiating element 100). To offset this imbalance, the distal end of one (but not both) of the inner sides 156 of each dipole arm 154 is widened so that it extends closer to the adjacent dipole arm 154. In particular, inner side 156-1 of first dipole arm 154-1 extends closer to inner side 156-2 of third dipole arm 154-3, and inner side 156-1 of second dipole arm 154-2 extends closer to inner side 156-2 of fourth dipole arm 154-4. Facing widened portions at the distal ends of inner sides 156 of dipole arms 154 form a pair of capacitors 170-1, 170-2 that offset the aforementioned imbalance caused by the use of a single feed shank printed circuit board 110. A plane defined by dielectric substrate 142 of dipole radiator printed circuit board 140 may intersect first capacitor 170-1 and second capacitor 170-2.

[0094] In the depicted embodiment, the dipole arms 154 themselves do not include any stealth structures. Instead, the mid-band radiating element 100 includes a plurality of metallic stealth structures 162 implemented in the second metallization pattern 160 of the dipole radiator printed circuit board 140. Each metallic stealth structure 162 is formed behind a respective one of the dipole arms 154. Each metallic stealth structure 162 includes four small metal pads 164-1 through 164-4 that overlap the four corners of the dipole arm 154, such that each small metal pad 164 is capacitively coupled to the dipole arm 154. As used herein, a first element on a printed circuit board "overlaps" a second element if an axis perpendicular to the major surface of the printed circuit board passes through both the first and second elements. Each metallic stealth structure 162 also includes four larger metal pads 166-1 through 166-4. Each larger metal pad 166 is galvanically connected to a respective one of the smaller metal pads 164. These connections are formed at the corners of the smaller and larger metal pads 164 and 166, such that a relatively narrow metal strip connects the smaller metal pad 164 to the larger metal pad 166, thereby providing series inductance. Both sides of each larger metal pad 166 are also coupled to a corresponding edge of the dipole arm 154. These inductive and capacitive couplings form multiple resonant circuits, which can be electrically connected in series, for example. These resonant circuits are configured to pass RF current in the operating frequency band of the radiating element 100 while suppressing RF current in a different frequency band. The different frequency band may be the operating frequency band of another array of radiating elements included in the base station antenna that includes the radiating element 100. Thus, the metallic stealth structure 162 allows the dipole arm 154 to be a non-stealth structure while still ensuring that the radiating element 100 is stealthy relative to the RF radiation in the operating frequency band of nearby higher-band radiating elements. Of course, a stealth structure can also be included in the dipole arm 154 to provide a higher degree of stealth.

[0095] Each metallic cloaking structure 162 can include multiple resonant circuits. For example, each combination of a smaller metallic pad 164 and a larger metallic pad 166 can form a resonant circuit with a dipole arm 154. These resonant circuits can be electrically arranged in series and / or in parallel. While the radiating element 100 includes metallic cloaking structures 162 that operate by forming resonant circuits with the dipole arms, it should be understood that in other embodiments, metallic cloaking structures 162 can be implemented using a metamaterial surface having a periodic arrangement that performs a cloaking function.

[0096] The mid-band radiating element 100 can exhibit a high degree of transparency to RF radiation in the frequency range of, for example, 3.4-4.0 GHz. The single feed stem PCB 110 has relatively little metallization and is mounted such that, when the radiating element 100 is mounted in the passive / active antenna system 1, its major surface extends in both the forward F direction and the transverse T direction. Thus, when the high-band beamforming array 160 is electronically scanned in the azimuth plane (i.e., the antenna beam is scanned in the transverse direction T), the antenna beam is incident on the thin side surface of the feed stem PCB 110 and, therefore, largely does not "see" the metallization patterns 120, 130 on the feed stem PCB 110. The mid-band radiating element 100 also does not include any directors that could otherwise reflect high-band RF radiation. Finally, the stealth structure 162 stealths the dipole arms 154 so that, in most cases, high-band RF radiation will only pass through the dipole radiator PCB 140. Simulations indicate that when the mid-band radiating element 100 is positioned in front of the high-band beamforming array 160 in the passive / active base station antenna 1 , the directionality of the high-band beamforming array 160 is only degraded by approximately 0.1 dB (averaged across the 3.4-4.0 GHz operating frequency range).

[0097] Reference again Figures 2A-2F According to an embodiment of the present invention, a radiating element 100 is provided. The radiating element includes a feed stem printed circuit board 110, which includes a first RF transmission line 114-1 and a second RF transmission line 114-2. The radiating element 100 also includes a first dipole radiator 152-1 coupled to the first RF transmission line 114-1, the first dipole radiator 152-1 including a first dipole arm 154-1 and a second dipole arm 154-2; and a second dipole radiator 152-2 coupled to the second RF transmission line 114-2, the second dipole radiator 152-2 including a third dipole arm 154-3 and a fourth dipole arm 154-4. The feed stem printed circuit board 110 is positioned between the first dipole arm 152-1 and the third dipole arm 152-3, and between the second dipole arm 152-2 and the fourth dipole arm 152-4.

[0098] Each of dipole arms 154 may include a metal ring with an open interior. Each of dipole arms 154 is positioned adjacent to two other dipole arms 154, such that when viewed from the front, the four dipole arms 154 together define a square 157. Each of dipole arms 154 has a first inner side 156-1 and a second inner side 156-2, each extending outward from the center of the square, and a first outer side 158-1 and a second outer side 158-2, each defining a corresponding portion of the perimeter of square 157. A first coupling amount between first dipole arm 154-1 and third dipole arm 154-3 exceeds a second coupling amount between first dipole arm 154-1 and fourth dipole arm 154-4. Similarly, a third coupling amount between second dipole arm 152-2 and fourth dipole arm 152-4 exceeds a fourth coupling amount between second dipole arm 152-2 and third dipole arm 152-3. The difference between the first coupling amount and the second coupling amount can be provided by a first capacitor 170-1, which is disposed between the distal end of the first inner side 156-1 of the first dipole arm 154-1 and the distal end of the second inner side 156-2 of the third dipole arm 154-3. The difference between the third coupling amount and the fourth coupling amount can be provided by a second capacitor 170-2, which is disposed between the distal end of the first inner side 156-1 of the second dipole arm 154-2 and the distal end of the second inner side 156-2 of the fourth dipole arm 154-4. Capacitor 170 can be configured to improve isolation between the two dipole radiators 152.

[0099] Radiating element 100 can be one of multiple lower-band radiating elements included in a base station antenna, such as a passive / active antenna system 1. For example, some or all of mid-band array 140 can be implemented using radiating element 100. A beamforming array 160 of higher-band radiating elements 162 is mounted behind radiating element 100. Radiating element 100 can also include first through fourth metallic cloaking structures 162-1, 162-4 overlapping respective first through fourth dipole arms 154-1, 154-4, wherein metallic cloaking structures 162 are configured to render respective dipole arms 154 substantially transparent to RF radiation emitted by higher-band radiating elements 162. Dipole arms 154 and metallic cloaking structures 162 can each be formed on a dielectric substrate 142 of a dipole radiator printed circuit board 140. The array 160 of higher frequency band radiating elements 162 may be a multi-column array, where the columns extend in the longitudinal direction of the antenna 1 , and the first and second major surfaces of the feed handle printed circuit board 110 may extend forward from the reflector 122 of the antenna 1 and perpendicular to the longitudinal direction.

[0100] Still refer to Figures 2A-2FThe mid-band radiating element 100 includes a feed stem printed circuit board 110 including first and second RF transmission lines 114-1 and 114-2; a first dipole radiator 152-1 coupled to the first RF transmission line 114-1, including first and second dipole arms 154-1 and 154-2; and a second dipole radiator 152-2 coupled to the second RF transmission line 114-2, including third and fourth dipole arms 154-3 and 154-4. The feed stem printed circuit board 110 is positioned between the first and third dipole arms 154-1 and 154-3, and between the second and fourth dipole arms 154-2 and 154-4. The distal ends of the first and third dipole arms 154-1, 154-3 that face inwardly 156 are more closely spaced apart than the distal ends of the first and fourth dipole arms 154-1, 154-4 that face inwardly 156. The distal ends of the second and fourth dipole arms 154-2, 154-4 that face inwardly 156 can also be more closely spaced apart than the distal ends of the second and third dipole arms 154-2, 154-3 that face inwardly 156. The inwardly facing sides 156 of the first and third dipole arms 154-1, 154-3 are symmetrical about the first axis, and the inwardly facing sides 156 of the first and fourth dipole arms 154-1, 154-4 are symmetrical about the second axis. Similarly, inner sides 156 of the second and fourth dipole arms 154-2, 154-4 facing each other are symmetrical about the first axis, and inner sides 156 of the second and third dipole arms 154-2, 154-3 are symmetrical about the second axis.The feed stem printed circuit board 110 may extend along the first axis.

[0101] from Figures 2A-2F As can also be seen in the figure, mid-band radiating element 100 includes a first dipole radiator 152-1 and a second dipole radiator 152-2. The first dipole radiator includes first and second dipole arms 154-1 and 154-2, and the second dipole radiator includes third and fourth dipole arms 154-3 and 154-4. Radiating element 100 also includes first and fourth metallic stealth structures 162-1 and 162-4 that form resonant circuits with the respective first and fourth dipole arms 154-1 and 154-4. These resonant circuits can be configured to allow current in the operating frequency band of radiating element 100 to flow through dipole arms 154 while preventing current in another operating frequency band from flowing through dipole arms 154. A first amount of coupling between the first dipole arm 154 - 1 and the third dipole arm 154 - 3 exceeds a second amount of coupling between the first dipole arm 154 - 1 and the fourth dipole arm 154 - 4 .

[0102] Figure 3A is a schematic front view of a mid-band crossed-dipole radiating element 200. Figures 2A-2F A modified version of the mid-band crossed dipole radiating element 100. Figure 2A and Figure 3A As can be seen, radiating element 200 is similar to radiating element 100 , but radiating element 200 includes four identical and therefore balanced dipole arms 254 . Figure 3B It is a comparison Figure 2A and Figure 3A A graph showing the cross-polarization isolation performance of the radiating element. Figure 3B As shown in , the cross-polarization isolation across the 1695-2690 MHz operating band ranges from -22 dB to -14 dB for the mid-band radiating element 200. In comparison, the cross-polarization isolation across the 1695-2690 MHz operating band ranges from -27 dB to -21 dB for the mid-band radiating element 100, which means that the worst-case cross-polarization isolation is improved by approximately 7 dB when using the unbalanced radiating element 100.

[0103] Figure 4 is a schematic front shadow diagram of a mid-band cross-polarization radiating element 300 according to another embodiment of the present invention.

[0104] By comparison Figure 2A and Figure 4 It can be seen that the mid-band radiating element 300 can be identical to the radiating element 100, except that the radiating element 300 has a different design for its dipole radiator 352 and dipole arm 354. In particular, Figure 4As best seen in the lead-out diagram in FIG, the annular square metal ring forming each dipole arm 354 has a plurality of inwardly extending slots 372A and a plurality of outwardly extending slots 372B that omit the metal. In some embodiments, the slots 372 can extend generally perpendicular to the direction of transient current flow along the dipole arm 354 (current flowing outward from the center of the dipole radiator printed circuit board 340 or inward from the distal end of the dipole arm 354 along the four sides of the dipole arm 354). The inwardly extending slots 372A and the outwardly extending slots 372B can alternate along the length of each dipole arm 354, forcing the current to flow along an undulating path, thereby increasing the electrical length of each dipole arm 354 compared to the same dipole arm without the slots 372A, 372B. As a result, the overall size of the dipole arm 354 can be reduced compared to the dipole arm 154 while still covering the same operating frequency band. Smaller dipole arms 354 mean that radiating element 300 takes up less space in a base station antenna and may also include less metal, thereby causing less interference with any higher frequency band radiating elements mounted behind radiating element 300 .

[0105] The first inner side 156-1 and the second outer side 158-2 form a first metal arm segment 174-1 of each dipole arm 354, and the second inner side 156-2 and the first outer side 158-1 form a second metal arm segment 174-1 of each dipole arm 354. The first (base) end of the first metal arm segment 174-1 can be physically connected to the first (base) end of the second metal arm segment 174-1, and the second (distal) end of the first metal arm segment 174-1 can be physically connected to the second (distal) end of the second metal arm segment 174-2. Thus, the first and second metal arm segments of each dipole arm form a conductive loop with an open interior. In other embodiments, the first (base) end of the first metal arm segment 174 of each dipole arm 354 may not be physically connected to each other, and / or the second (distal) end of the first metal arm segment 174 of each dipole arm 354 may not be physically connected to each other. The same is true for other radiating elements disclosed herein.

[0106] Although the slots 372A, 372B are shown as extending perpendicular to the longitudinal axis of each of the inner side 156 and the outer side 158 of the dipole arm 354, embodiments of the present invention are not limited thereto. In other embodiments, the inwardly extending slots 372A and / or the outwardly extending slots 372B may extend at an oblique angle relative to the longitudinal axis of some or all of the inner side 156 and / or the outer side 158 of the dipole arm 354. The number of slots 372A, 372B and / or the spacing between the slots 372A, 372B may also vary from that shown, and the spacing between the slots need not be constant (e.g., Figure 4). In other embodiments, the width of the inner side 156 and / or the outer side 158 of the dipole arm 354 can be increased, and the length of the slots 372A, 372B can be increased, to further increase the electrical length of the dipole arm 354 compared to its physical length.

[0107] Therefore, if Figure 4 As shown in FIG, according to another embodiment of the present invention, a radiating element 300 is provided, the radiating element including a first dipole radiator 352-1 and a second dipole radiator 352-2, the first dipole radiator including a first dipole arm 354-1 and a second dipole arm 354-2, and the second dipole radiator including a third dipole arm 354-3 and a fourth dipole arm 354-4. Each of the dipole arms 354 includes a first metal dipole arm segment and a second metal dipole arm segment 174-1, 174-2 having a plurality of slots 372A, 372B in which metal is omitted, wherein the slots 372A, 372B are configured to increase the length of a corresponding current path along each of the first metal dipole arm segment and the second metal dipole arm segment 174-1, 174-2.

[0108] The bases of the first and second metal dipole arm segments 174-1, 174-2 of each dipole arm 354 are physically connected to one another, and their distal ends are also physically connected to one another. Thus, each dipole arm 354 includes an annular metal ring 176 having an open interior. The slots may include outwardly extending slots 372B extending outward from the interior of the metal ring and inwardly extending slots 372A extending inward from the exterior of the metal ring 176. Each of the dipole arms 354 may include at least two or three outwardly extending slots 372B and at least two or three inwardly extending slots 372A, wherein the outwardly extending slots 372B and the inwardly extending slots 372A are arranged in an alternating manner. Each of the metal rings 176 may generally define a corresponding annular square. A majority of the slots 372A, 372B on each side of each annular square may extend perpendicular to the longitudinal direction of that side of the corresponding annular square. The outer side of each annular square may have a substantially constant width. The slots 372A, 372B may have equal widths.

[0109] Figures 5A-5C is a schematic front shadow view of a dipole radiator printed circuit board of a mid-band radiating element according to an additional embodiment of the present invention.

[0110] First reference Figure 5A , shows a dipole radiator printed circuit board 440 that is similar to the dipole radiator printed circuit board 140 of the mid-band radiating element 100, but having a stealth structure 462 instead of the stealth structure 162. In particular, as can be seen by comparing Figure 2E and Figure 5AAs can be seen, the only difference between dipole radiator PCB 440 and dipole radiator PCB 140 is that larger metal pad 166 of dipole radiator PCB 140 is a solid metal pad, while larger metal pad 466 of dipole radiator PCB 440 is a ring-shaped square pad with an open interior. The reduced amount of metal in pad 466 can result in less reflection of RF radiation emitted by nearby higher-band radiating elements. Omitting metal in the middle of larger metal pad 466 has little effect on capacitive coupling.

[0111] Figure 5B FIG2 is a schematic front view of a dipole radiator printed circuit board 540 according to yet another embodiment of the present invention. Dipole radiator printed circuit board 540 may be identical to dipole radiator printed circuit board 140, except that, in dipole radiator printed circuit board 540, larger metal pad 566 has metal-eliminating grooves 372A and 372B formed therein. Because dipole radiator printed circuit board 540 is essentially identical to dipole radiator printed circuit board 140, further description thereof will be omitted.

[0112] Figure 5C is a schematic front view of a dipole radiator printed circuit board 640 according to another additional embodiment of the present invention. The main differences between the dipole radiator printed circuit board 640 and the dipole radiator printed circuit boards 140, 340, 440, 540 are that in the dipole radiator printed circuit board 640, (1) some of the dipole arms 654 are implemented on the first major surface of the dielectric substrate 642, while other of the dipole arms 654 are implemented on the second major surface of the dielectric substrate 642, and (2) the stealth structures 662-1, 662-3 are implemented on the first major surface of the dielectric substrate 642, while the stealth structures 662-2, 662-4 are implemented on the second major surface of the dielectric substrate 642. The dipole radiator printed circuit board 640 is intended to illustrate that each dipole arm and each stealth structure in the mid-band radiating element according to an embodiment of the present invention can be implemented on either side of its corresponding dipole radiator printed circuit board. Figure 5C It can also be seen that the capacitor 170 provided in the mid-band radiating element 100 between selected ones of the dipole arms 154 is omitted in the dipole radiator printed circuit board 640. Figures 6A-6B As discussed, according to another embodiment of the present invention, a mid-band radiating element similar to mid-band radiating element 100 but including a balanced feed stem is provided. When a balanced feed stem is used, capacitors 170-1, 170-2 will typically be omitted.

[0113] Figure 6A and Figure 6Bis a schematic front shadow diagram of a multi-band radiating element according to another embodiment of the present invention. In particular, Figure 6A A mid-band radiating element 700 is shown, which includes the mid-band radiating element described above with reference to Figure 5C A dipole radiator printed circuit board 640 and a feed stem 710 including a pair of coaxial feed cables 712-1, 712-2 are discussed. Figure 6B A mid-band radiating element 800 is shown that includes a dipole radiator printed circuit board 840 that is identical to the dipole radiator printed circuit board 140, except that the dipole radiator printed circuit board 840 does not include capacitors 170-1, 170-2. Capacitors 170-1, 170-2 are omitted from the mid-band radiating element 800 because the radiating element 800 includes a feed stem 810 that includes a conventional pair of feed stem printed circuit boards in a "cross" arrangement that provides a balanced feed to the dipole radiator printed circuit board 840. It should be understood that any of the radiating elements discussed above according to embodiments of the present invention may include Figure 6A Dual coaxial cable feed handle or Figure 6B If a balanced feed stem is provided, the capacitor between the dipole arms can be omitted.

[0114] Figure 7A is a schematic front shadow diagram of a mid-band radiating element 900 according to yet another embodiment of the present invention. Figures 7B to 7D is a graph showing the current distribution on the radiating element in response to different types of higher frequency band radiation Figure 7A An enlarged schematic front shadow view of a corner of a mid-band radiating element of FIG. The mid-band radiating element 900 is similar to Figures 2A to 2F The mid-band radiating element 100 is described above, and therefore the following description will focus on the differences between the two radiating elements 100, 900.

[0115] By comparison Figure 2E and Figure 7AAs can be seen, mid-band radiating element 900 differs from radiating element 100 in two ways. First, mid-band radiating element 900 includes first through fourth narrow right-angle slots 980-1, 980-4, disposed in the outer corners of respective first through fourth dipole arms 954-1, 954-4. In the depicted embodiment, each right-angle slot 980 includes first and second straight slot segments 982, 984, which intersect to form right-angle slot 980, with metallization omitted. The length of each right-angle slot 980 can be ¼ wavelength of a frequency within the operating band of a nearby higher-band radiating element (not shown). For example, the length of each right-angle slot 980 can be ¼ wavelength of a frequency within the center frequency of the operating band of the nearby higher-band radiating element or within the lower half of the operating band of the nearby higher-band radiating element. Here, the length of the slot (or trace) that does not extend completely along a single axis refers to the sum of the lengths of the individual segments of the slot (or trace). Therefore, the length of each right-angle slot 980 is the sum of the lengths of the first straight slot segment and the second straight slot segment 982, 984.

[0116] Secondly, the mid-band radiating element 900 includes first to fourth narrow right-angle traces 986-1 to 986-4, which are radially disposed outside the outer corners of the corresponding first to fourth dipole arms 954-1 to 954-4. In the depicted embodiment, the first to fourth narrow right-angle traces 986-1 to 986-4 are disposed in the same metallization layer as the first to fourth dipole arms 954-1 to 954-4 and are separated from the corresponding dipole arms 954 by a narrow gap, so that the narrow right-angle traces 986 are capacitively coupled to the corresponding dipole arms 954. The length of each narrow right-angle trace 986 can be 1 / 4 of the wavelength of a frequency within the operating band of a nearby higher-band radiating element (not shown). For example, the length of each narrow right-angle trace 986 may be 1 / 4 of a wavelength of the center frequency of the operating band of the nearby higher-band radiating element or a frequency in the lower half of the operating band of the nearby higher-band radiating element.

[0117] The right-angle slot 980 and the narrow right-angle traces 986-1 through 986-4 are designed to improve the stealth performance of the mid-band radiating element 900, particularly at the lower end of the operating frequency range of the nearby high-band radiating element, compared to the mid-band radiating element 100. The right-angle slot 180 and the narrow right-angle traces 986-1 through 986-4 are designed so that they do not adversely affect the mid-band antenna beam generated by the mid-band radiating element 900.

[0118] Figure 7Bis an enlarged schematic front shaded view of a corner of one of the dipole arms 954 of the mid-band radiating element 900 illustrating the current distribution on the dipole arm 954 in response to different types of higher frequency band radiation. In particular, Figure 7B 9 shows the current distribution on the dipole arm 954 in response to higher frequency band RF radiation (emitted by a nearby radiating element operating in the 3.4 GHz to 4.0 GHz band) when the narrow right angle trace 986 is not present. Figure 7B As shown, the direction of the high-frequency current outside the right-angle slot 980 is opposite to the direction of the high-frequency current inside the right-angle slot 980. Therefore, the right-angle slot 980 helps to cancel the high-frequency current, thereby improving the stealth performance of the dipole arm 954.

[0119] Figure 7C 9 is a schematic front shaded view of a corner of one of the dipole arms 954 of the mid-band radiating element 900, illustrating the current distribution on the dipole arm 954 when the narrow right-angle trace 986 is included. Figure 7C As shown, the direction of the high-band current on the right-angle trace 986 is opposite to the direction of the high-band current on the dipole arm 954. Therefore, the right-angle trace 986 helps to cancel the high-band current, thereby improving the stealth performance of the dipole arm 954.

[0120] Please note that Figure 7C The direction of the high-frequency current around the outside of the right-angle slot 180 is not opposite to the direction of the high-frequency current inside the right-angle slot 980. This is because Figure 7B shows the high-band current distribution on a -45° polarized mid-band dipole arm 954 in response to RF radiation emitted by a nearby -45° polarized high-band dipole radiator, while Figure 7C The high-band current distribution on the +45° polarized mid-band dipole arm 954 is shown in response to RF radiation emitted by a nearby -45° polarized high-band dipole radiator. Figure 7D shows that if a high-band current is formed in response to RF radiation emitted by a nearby +45° polarized high-band dipole radiator, then Figure 7C Shown is how the current distribution changes.

[0121] It should be understood that many modifications may be made to the radiating elements discussed above without departing from the scope of the present invention. For example, while the radiating elements according to embodiments of the present invention are described above as mid-band radiating elements that are invisible within the high-band frequency range, in other embodiments, the radiating elements may be low-band radiating elements that are invisible within the mid-band operating frequency range. As another example, while the dipole arms of the mid-band radiating elements described above are implemented in a dipole radiator printed circuit board, it should be understood that embodiments of the present invention are not limited thereto. For example, in other embodiments, the dipole arms may be implemented as sheet metal dipole arms or may be implemented using other metal structures.

[0122] 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 above-described cellular communication systems.

[0123] 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.

[0124] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the scope of the present invention. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0125] It will be understood that when an element is described as being "on" another element, the element may be directly on the other element, or there may 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 may be directly connected or coupled to the other element, or there may 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.).

[0126] 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.

[0127] In this context, the term "substantially" means within + / - 10%.

[0128] The terms used in this article 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 also intended to include the plural forms, 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 described features, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, operations, elements, parts and / or their groupings.

[0129] 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 printed circuit board comprising a first radio frequency ("RF") transmission line and a second RF transmission line; a first dipole radiator coupled to the first RF transmission line, the first dipole radiator comprising a first dipole arm and a second dipole arm; as well as a second dipole radiator coupled to the second RF transmission line, the second dipole radiator comprising a third dipole arm and a fourth dipole arm, A first coupling amount between the first dipole arm and the third dipole arm exceeds a second coupling amount between the first dipole arm and the fourth dipole arm.

2. The radiating element of claim 1, wherein a third coupling quantity between the second dipole arm and the fourth dipole arm exceeds a fourth coupling quantity between the second dipole arm and the third dipole arm.

3. The radiating element of claim 1, wherein the feed stem printed circuit board is positioned between the first dipole arm and the third dipole arm and between the second dipole arm and the fourth dipole arm.

4. The radiating element of claim 2 , wherein each of the first to fourth dipole arms is positioned immediately adjacent to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front, wherein each of the first to fourth dipole arms has first and second inner sides, each extending outward from a center of the square, and first and second outer sides, each defining a respective portion of a perimeter of the square. 5 . The radiating element of claim 4 , wherein each of the first to fourth dipole arms comprises a metal ring having an open interior.

6. The radiating element of claim 5 , wherein the difference between the first coupling amount and the second coupling amount is provided by a first capacitor, the first capacitor being disposed between a first inner distal end of the first dipole arm and a second inner distal end of the third dipole arm.

7. The radiating element of claim 6 , wherein the difference between the third coupling amount and the fourth coupling amount is provided by a second capacitor, the second capacitor being disposed between a first inner distal end of the second dipole arm and a second inner distal end of the fourth dipole arm.

8. The radiating element of claim 7, wherein the first capacitor and the second capacitor are configured to improve isolation between the first dipole radiator and the second dipole radiator.

9. The radiating element and base station antenna combination of claim 1, wherein the radiating element is one of a plurality of lower frequency band radiating elements and an array of higher frequency band radiating elements is mounted behind the radiating element.

10. The radiating element of claim 9, further comprising first to fourth metal stealth structures overlapping the corresponding first to fourth dipole arms, wherein the first to fourth metal stealth structures are configured to make the corresponding first to fourth dipole arms substantially transparent to the RF radiation emitted by the higher frequency band radiating element.

11. The radiation element of claim 10, wherein the first to fourth dipole arms and the first to fourth metal stealth structures are formed on a dielectric substrate of a dipole radiator printed circuit board.

12. The radiating element of claim 10 , wherein the array of higher frequency band radiating elements comprises an array of multiple columns of higher frequency band radiating elements, wherein the columns extend in the longitudinal direction of the base station antenna, and wherein the first and second major surfaces of the feed handle printed circuit board extend forward from the reflector of the base station antenna and perpendicular to the longitudinal direction.

13. The radiation element according to claim 10, wherein the first to fourth dipole arms are installed adjacent to a front end of the feeding handle, and the first to fourth metal stealth structures are installed behind the corresponding first to fourth dipole arms.

14. The radiating element of claim 9, wherein each of the first through fourth dipole arms comprises a metal ring having an open interior.

15. The radiating element of claim 14, wherein the metal ring of the first dipole arm includes a slot from which metal is omitted.

16. The radiating element of claim 15, wherein the slot comprises a first slot segment and a second slot segment intersecting to define a right angle.

17. The radiating element of claim 15, wherein the slot is positioned adjacent an outer corner of the first dipole arm.

18. The radiating element of claim 15, wherein the length of the slot is one quarter wavelength of a frequency within the operating band of the higher frequency band radiating element.

19. The radiating element of claim 14, further comprising first to fourth metal traces positioned radially outward of the respective first to fourth dipole arms and configured to capacitively couple with the respective first to fourth dipole arms.

20. The radiating element of claim 19, wherein each of the first to fourth metal traces has a right-angle shape.

21. The radiating element of claim 20, wherein a length of each of the first through fourth metal traces is one quarter wavelength of a frequency within an operating band of the higher frequency band radiating element.

22. A radiating element, comprising: a feed handle printed circuit board comprising a first radio frequency ("RF") transmission line and a second RF transmission line; a first dipole radiator coupled to the first RF transmission line, the first dipole radiator comprising a first dipole arm and a second dipole arm; as well as a second dipole radiator coupled to the second RF transmission line, the second dipole radiator comprising a third dipole arm and a fourth dipole arm, wherein the feed handle printed circuit board is positioned between the first dipole arm and the third dipole arm and between the second dipole arm and the fourth dipole arm, and wherein the inwardly facing distal ends of the first and third dipole arms are more closely spaced apart than the inwardly facing distal ends of the first and fourth dipole arms.

23. The radiating element of claim 22, wherein the inwardly facing distal ends of the second and fourth dipole arms are more closely spaced apart than the inwardly facing distal ends of the second and third dipole arms.

24. The radiating element of claim 23, wherein the inwardly facing sides of the first and third dipole arms are symmetric about a first axis, and the inwardly facing sides of the first and fourth dipole arms are symmetric about a second axis.

25. The radiating element of claim 24, wherein the inwardly facing sides of the second and fourth dipole arms are symmetric about the first axis, and the inwardly facing sides of the second and third dipole arms are symmetric about the second axis.

26. The radiating element of claim 25, wherein the feed shank printed circuit board extends along the first axis.

27. The radiating element of claim 22, wherein each of the first to fourth dipole arms is positioned next to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front.

28. The radiating element of claim 27, wherein each of the first through fourth dipole arms comprises a metal ring having an open interior.

29. The radiating element of claim 22, wherein the first RF transmission line is coupled to the first dipole radiator and the second RF transmission line is coupled to the second dipole radiator.

30. The radiating element and base station antenna combination of claim 23, wherein the radiating element is one of a plurality of lower frequency band radiating elements and an array of higher frequency band radiating elements is mounted behind the radiating element.

31. The radiating element of claim 30, further comprising first to fourth metal stealth structures overlapping the corresponding first to fourth dipole arms, wherein the first to fourth metal stealth structures are configured to make the corresponding first to fourth dipole arms substantially transparent to the RF radiation emitted by the higher frequency band radiating element.

32. The radiation element of claim 31, wherein the first to fourth dipole arms and the first to fourth metal stealth structures are formed on a dielectric substrate of a dipole radiator printed circuit board.

33. A radiating element as described in claim 31, wherein the array of higher frequency band radiating elements comprises an array of multiple columns of higher frequency band radiating elements, wherein the columns extend in the longitudinal direction of the base station antenna, and wherein the first major surface and the second major surface of the feed handle printed circuit board extend forward from the reflector of the base station antenna and perpendicular to the longitudinal direction.

34. The radiation element of claim 31, wherein the first to fourth dipole arms are installed adjacent to a front end of the feeding handle, and the first to fourth metal stealth structures are installed behind the corresponding first to fourth dipole arms.

35. The radiating element of claim 30, wherein each of the first through fourth dipole arms comprises a metal ring having an open interior.

36. The radiating element of claim 30, wherein the metal ring of the first dipole arm includes a slot from which the metal is omitted.

37. The radiating element of claim 36, wherein the slot comprises a first slot segment and a second slot segment intersecting to define a right angle.

38. The radiating element of claim 36, wherein the slot is positioned adjacent an outer corner of the first dipole arm.

39. The radiating element of claim 36, wherein the length of the slot is one quarter wavelength of a frequency within an operating band of the higher frequency band radiating element.

40. The radiating element of claim 36, further comprising first to fourth metal traces positioned radially outward of the respective first to fourth dipole arms and configured to capacitively couple with the respective first to fourth dipole arms.

41. The radiating element of claim 40, wherein each of the first through fourth metal traces has a right-angle shape.

42. The radiating element of claim 41 , wherein the length of each of the first through fourth metal traces is one quarter wavelength of a frequency within an operating band of the higher frequency band radiating element.

43. A radiating element, comprising: a first dipole radiator comprising a first dipole arm and a second dipole arm, the first dipole radiator being configured to transmit and receive electromagnetic radiation within a first operating frequency band; as well as a second dipole radiator, the second dipole radiator comprising a third dipole arm and a fourth dipole arm, the second dipole radiator being configured to transmit and receive electromagnetic radiation within the first operating frequency band; as well as first to fourth metal stealth structures, wherein the first to fourth metal stealth structures form a resonant circuit with the corresponding first to fourth dipole arms, wherein the resonant circuit is configured to allow current in the first operating frequency band to flow through the first to fourth dipole arms, while preventing current in the second operating frequency band from flowing through the first to fourth dipole arms, A first coupling amount between the first dipole arm and the third dipole arm exceeds a second coupling amount between the first dipole arm and the fourth dipole arm.

44. The radiating element of claim 43, wherein a third coupling quantity between the second dipole arm and the fourth dipole arm exceeds a fourth coupling quantity between the second dipole arm and the third dipole arm.

45. The radiation element of claim 43, wherein each of the first to fourth metal stealth structures forms a multi-stage resonant circuit with a corresponding dipole arm of the first to fourth dipole arms.

46. ​​The radiating element of claim 45, wherein each multi-stage resonant circuit comprises a plurality of resonant circuits connected in series with each other.

47. The radiating element of Claim 43, wherein each of the first through fourth dipole arms comprises a looped dipole arm.

48. The radiating element of claim 43, further comprising a feed stem printed circuit board comprising a first radio frequency ("RF") transmission line coupled to the first dipole radiator and a second RF transmission line coupled to the second dipole radiator.

49. The radiating element of claim 48, wherein the feed stem printed circuit board is positioned between the first and third dipole arms and between the second and fourth dipole arms.

50. The radiating element of claim 44, wherein each of the first to fourth dipole arms is positioned adjacent to two other of the first to fourth dipole arms such that the first to fourth dipole arms together define a square when viewed from the front, and wherein each of the first to fourth dipole arms comprises a metal ring having an open interior.

51. The radiating element of claim 44, wherein the difference between the first coupling amount and the second coupling amount is provided by a first capacitor disposed between a first inner distal end of the first dipole arm and a second inner distal end of the third dipole arm.

52. The radiating element of claim 51 , wherein the difference between the third coupling amount and the fourth coupling amount is provided by a second capacitor disposed between a first inner distal end of the second dipole arm and a second inner distal end of the fourth dipole arm.

53. The radiating element of claim 52, wherein the first capacitor and the second capacitor are configured to improve isolation between the first dipole radiator and the second dipole radiator.

54. The radiating element of claim 43, wherein each of the first to fourth dipole arms comprises a metal ring having an open interior, wherein the metal ring is provided with a corresponding slot in which the metal in the metal ring of each of the first to fourth dipole arms is omitted.

55. The radiating element of Claim 54, wherein each slot comprises a first slot segment and a second slot segment that intersect to define a right angle.

56. The radiating element of Claim 55, wherein each slot is positioned adjacent an outer corner of a respective one of the first to fourth dipole arms.

57. The radiating element of claim 56, further comprising first to fourth metal traces positioned radially outward of the respective first to fourth dipole arms and configured to capacitively couple with the respective first to fourth dipole arms.

58. The radiating element of claim 57, wherein each of the first through fourth metal traces has a right-angle shape.

59. A radiating element, comprising: a first dipole radiator comprising a first dipole arm and a second dipole arm; as well as a second dipole radiator comprising a third dipole arm and a fourth dipole arm, Each of the first to fourth dipole arms includes a first metal dipole arm segment and a second metal dipole arm segment having a plurality of slots with metal omitted, the slots being configured to increase the length of a respective current path along each of the first metal dipole arm segment and the second metal dipole arm segment.

60. The radiating element of Claim 59, wherein the first and second metallic dipole arm segments of each of the first to fourth dipole arms together form respective first to fourth metallic rings having an open interior.

61. The radiating element of claim 60 , wherein for each of the first to fourth dipole arms, some of the slots are outwardly extending slots extending outward from an interior of a corresponding one of the first to fourth metal rings, while other of the slots are inwardly extending slots extending inward from an exterior of the corresponding one of the first to fourth metal rings.

62. The radiating element of claim 60, wherein for each of the first through fourth dipole arms, at least two outwardly extending slots and at least two inwardly extending slots are arranged in an alternating manner.

63. The radiating element of claim 60, wherein for each of the first through fourth dipole arms, at least three outwardly extending slots and at least three inwardly extending slots are arranged in an alternating manner.

64. The radiating element of claim 60, wherein each of the first to fourth metal rings substantially defines a respective annular square, and wherein a majority of the slots in each side of each of the annular squares extend perpendicular to a longitudinal direction of the side of the respective annular square.

65. The radiating element of claim 59, further comprising a feed stem having a base and a distal end, wherein the first dipole radiator and the second dipole radiator are mounted adjacent the distal end of the feed stem.

66. The radiating element of claim 59, wherein said slots have equal widths.

67. The radiating element of claim 63, wherein the outside of each annular square has a substantially constant width.

68. The radiation element of claim 59, further comprising first to fourth metal stealth structures overlapping the corresponding first to fourth dipole arms.

69. A radiating element, comprising: a first dipole radiator comprising a first dipole arm and a second dipole arm; as well as a second dipole radiator comprising a third dipole arm and a fourth dipole arm, Each of the first to fourth dipole arms includes a metal ring having an open interior, and a corresponding slot is provided in the metal ring in which the metal is omitted.

70. The radiating element of Claim 69, wherein each slot comprises a first slot segment and a second slot segment that intersect to define a respective right angle.

71. The radiating element of Claim 70, wherein each slot is positioned adjacent an outer corner of each of the respective first through fourth dipole arms.

72. The radiating element of claim 69, further comprising first to fourth metal traces positioned radially outward of the respective first to fourth dipole arms and configured to capacitively couple with the respective first to fourth dipole arms.

73. The radiating element of claim 72, wherein each of the first through fourth metal traces has a right-angle shape.

Images