CN117916954A

CN117916954A - Broadband decoupling radiating element and base station antenna having such radiating element

Info

Publication number: CN117916954A
Application number: CN202280059736.9A
Authority: CN
Inventors: 孙斌; 吴博; 张建; 薛成; 李曰民; P·J·必思鲁勒斯; 吴利刚
Original assignee: Commscope Technologies LLC
Current assignee: Outdoor Wireless Network Co ltd
Priority date: 2021-09-08
Filing date: 2022-08-25
Publication date: 2024-04-19

Abstract

The antenna includes a first radiating element and a second radiating element configured to operate in respective operating frequency bands. The first radiating element includes a first dipole arm having a first conductive path and a second conductive path positioned behind the first conductive path. The first conductive path includes a plurality of first segments and the second conductive path includes a plurality of second segments, wherein a subset of the first segments overlap respective ones of the second segments to form a plurality of pairs of overlapping first and second segments. At least some of the pairs of overlapping segments are configured such that the instantaneous direction of the first current formed on the first segment in response to RF radiation emitted by the second radiating element will be substantially opposite to the instantaneous direction of the second current formed on the second segment in response to RF radiation.

Description

Broadband decoupling radiating element and base station antenna having such radiating element

Cross Reference to Related Applications

The present application claims priority from U.S. c. ≡119 to U.S. provisional patent application serial No. 63/241,676 filed on 8 of 2021 and U.S. provisional patent application serial No. 63/342,759 filed on 17 of 2022, each of which is incorporated herein by reference in its entirety.

Background

The present invention relates generally to radio communications, and more particularly to a base station antenna for a cellular communication system.

Cellular communication systems are well known in the art. In a cellular communication system, a geographical area is divided into a series of areas called "cells" that are served by corresponding base stations. A base station may include one or more antennas configured to provide two-way radio frequency ("RF") communication with mobile users within a cell served by the base station. In many cases, each base station is divided into "sectors". In one common configuration, a hexagonally shaped cell is divided into three 120 ° sectors in the azimuth plane, and each sector is served by one or more base station antennas having an azimuth half-power beamwidth ("HPBW") of about 65 °. Typically, the base station antennas are mounted on towers or other elevated structures, wherein a radiation pattern (also referred to herein as an "antenna beam") is generated by the outwardly directed base station antennas. Base station antennas are typically implemented as linear or planar phased arrays of radiating elements.

To accommodate the increasing cellular traffic, cellular operators have increased cellular services in various new frequency bands. While in some cases a single array of so-called "wideband" or "ultra-wideband" radiating elements may be used to provide service in multiple frequency bands, in other cases different arrays of radiating elements must be used to support service in different frequency bands.

As the number of frequency bands has proliferated, and as sector divisions have become more prevalent (e.g., dividing a cell into six, nine, or even twelve sectors), the number of base station antennas deployed at a typical base station has increased significantly. However, there are often limitations on the number of base station antennas that can be deployed at a given base station due to, for example, local zone regulations and/or weight and wind load constraints of the antenna tower. In order to increase the capacity without further increasing the number of base station antennas, so-called multiband base station antennas comprising a plurality of arrays of radiating elements have been introduced. Multi-band base station antennas comprising arrays operating in three different frequency bands are now being developed. For example, base station antennas are now being deployed that include two linear arrays of "low band" radiating elements operating in some or all of the 694-960MHz bands, two linear arrays of "mid band" radiating elements operating in some or all of the 1427-2690MHz bands, and one or more multi-column (planar) arrays of "high band" radiating elements operating in some or all of the higher frequency bands, such as the 3.3-4.2GHz bands. Unfortunately, the different arrays may interact with each other, which may make it challenging to implement such a multi-band antenna while also meeting customer requirements related to the size (particularly the width) of the base station antenna.

Disclosure of Invention

According to an embodiment of the present invention, there is provided an antenna (e.g., a base station antenna) including: a reflector; a first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band; and a second radiating element extending forward from the reflector, the second radiating element configured to operate in a second operating frequency band that includes higher frequencies than the first operating frequency band. The first radiating element includes a first dipole radiator having a first dipole arm and a second dipole radiator having a third dipole arm and a fourth dipole arm. The first dipole arm includes a first conductive path and a second conductive path positioned behind the first conductive path. The first conductive path includes a plurality of first segments and the second conductive path includes a plurality of second segments, wherein a subset of the first segments overlap respective ones of the second segments in the subset of second segments to form a plurality of pairs of overlapping first and second segments. At least some of each pair of overlapping first and second segments are configured such that the instantaneous direction of a first current formed on the first segment in response to RF radiation emitted by the second radiating element will be substantially opposite to the instantaneous direction of a second current formed on the second segment in response to RF radiation emitted by the second radiating element.

In some embodiments, the first conductive path may be a first serpentine conductive path and the second conductive path may be a second serpentine conductive path.

In some embodiments, the first conductive path may be implemented in a first metal layer of a printed circuit board and the second conductive path may be implemented in a second metal layer of the printed circuit board.

In some embodiments, the first serpentine conductive path may be a plurality of first longitudinal segments extending substantially parallel to a longitudinal direction of the first dipole arm and a plurality of first transverse segments extending substantially perpendicular to the longitudinal direction of the first dipole arm. In some embodiments, the second serpentine conductive path may be a plurality of second longitudinal segments extending substantially parallel to the longitudinal direction of the first dipole arm and a plurality of second transverse segments extending substantially perpendicular to the longitudinal direction of the first dipole arm. In some embodiments, at least some of the pairs of overlapping first and second segments may be respective ones of the first and second lateral segments. In some embodiments, substantially all of the first lateral segments may overlap with respective ones of the second lateral segments.

In some embodiments, in at least some of the pairs of overlapping first and second segments, one of the first and second segments may fully overlap the other of the first and second segments.

In some embodiments, at least one of the first lateral segments may be wider than at least one of the first longitudinal segments.

In some embodiments, the first radiating element may further include a feed handle having a feed line, and the first conductive path may be galvanically connected to the feed line, and the second conductive path may be galvanically coupled to the feed handle.

In some embodiments, the first and second conductive paths of each of the first to fourth dipole arms may form respective closed loops.

In some embodiments, the first serpentine conductive path may be a wave structure having a first frequency and the second serpentine conductive path may be a wave structure having a second frequency different from the first frequency.

In some embodiments, the second dipole arm may include a third conductive path substantially identical to the first conductive path and a fourth conductive path substantially identical to the second conductive path, and the first dipole arm may overlap the second radiating element.

In some embodiments, the antenna may further include a third radiating element extending forward from the reflector, the third radiating element configured to operate in a third operating frequency band that includes higher frequencies than the second operating frequency band, wherein the second dipole arm overlaps the third radiating element. In some of these embodiments, the first dipole arm and the second dipole arm may be configured to be substantially transparent to RF signals in the second operating frequency band and in the third operating frequency band.

In some embodiments, the first radiating element may further include at least one feed stalk extending generally perpendicular to the reflector, and each of the first to fourth dipole arms may include first and second spaced apart conductive segments that together form a generally oval shape.

In some embodiments, the average length of the first lateral segment may be less than 1/4 of a wavelength corresponding to a center frequency of the second operating band.

In some embodiments, the average width of the first serpentine conductive path may be less than 0.05 of a wavelength corresponding to a center frequency of the second operating frequency band, and the average width of the second serpentine conductive path may be less than 0.05 of a wavelength corresponding to a center frequency of the second operating frequency band.

According to a further embodiment of the present invention, there is provided a radiating element comprising a first dipole radiator having a first dipole arm and a second dipole arm; and a second dipole radiator having a third dipole arm and a fourth dipole arm, wherein the first dipole arm includes a first serpentine conductive path extending from a base of the first dipole arm to a distal end of the first dipole arm and a second serpentine conductive path positioned rearward of the first serpentine conductive path.

In some embodiments, the first serpentine conductive path may be a plurality of first longitudinal segments extending generally parallel to the longitudinal direction of the first dipole arm and a plurality of first transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm, and the second serpentine conductive path may be a plurality of second longitudinal segments extending generally parallel to the longitudinal direction of the first dipole arm and a plurality of second transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm.

In some embodiments, at least some of the first lateral segments may overlap with respective ones of the second lateral segments.

In some embodiments, substantially all of the first lateral segments may overlap with respective ones of the second lateral segments.

In some embodiments, at least some of the first lateral segments may completely overlap with respective ones of the second lateral segments.

In some embodiments, the first radiating element may further include a feed handle having a feed line, and the first serpentine conductive path may be galvanically connected to the feed line, and the second serpentine conductive path may be galvanically coupled to the feed handle.

In some embodiments, the first serpentine conductive path and the second serpentine conductive path may form respective closed loops.

In some embodiments, the first serpentine conductive path can have a substantially oval shape.

In some embodiments, the second serpentine conductive path can have a generally oval shape.

In some embodiments, the first serpentine conductive path may be a plurality of first wave segments each having a wave structure, and a plurality of first transition segments connecting respective adjacent pairs of the first wave segments.

In some embodiments, the second serpentine conductive path may be a plurality of second wave segments each having a wave structure, and a plurality of second transition segments connecting respective adjacent pairs of second wave segments.

According to still other embodiments of the present invention, there is provided an antenna, such as a base station antenna, comprising: a reflector; a first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band, the first radiating element comprising a first dipole arm; and a second radiating element extending forward from the reflector, the second radiating element configured to operate in a second operating frequency band that includes higher frequencies than the first operating frequency band. The first dipole arm includes a first conductive path and a second conductive path spaced apart from each other. A first segment of the first conductive path overlaps a second segment of the second conductive path. The first dipole arms are configured such that first and second currents induced on respective first and second conductive paths in response to radio frequency ("RF") radiation emitted by the second radiating element each flow outwardly along the first dipole arms but in substantially opposite directions along respective first and second segments.

In some embodiments, the first radiating element may be a first dipole radiator and a second dipole radiator, the first dipole radiator including the first dipole arm and the second dipole arm, the second dipole radiator having a third dipole arm and a fourth dipole arm, and each dipole arm including a base adjacent a center of the first radiating element and a distal end positioned outside the base.

In some embodiments, the first segment may be one of the first lateral segments and the second segment may be one of the second lateral segments.

According to other embodiments of the present invention, an antenna (e.g., a base station antenna) is provided, the antenna comprising a reflector; a first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band; and a second radiating element extending forward from the reflector, the second radiating element configured to operate in a second operating frequency band that includes higher frequencies than the first operating frequency band. The antennas also include one or more parasitic elements that each include a first conductive path and a second conductive path positioned rearward of the first conductive path. The first conductive path includes a plurality of first segments and the second conductive path includes a plurality of second segments. The subset of first segments overlaps respective ones of the second segments in the subset of second segments to form a plurality of pairs of overlapping first and second segments. At least some of each pair of overlapping first and second segments are configured such that the instantaneous direction of a first current formed on the first segment in response to RF radiation emitted by the second radiating element will be substantially opposite to the instantaneous direction of a second current formed on the second segment in response to RF radiation emitted by the second radiating element.

In some embodiments, the first conductive path and the second conductive path may each be a serpentine conductive path. In some embodiments, the first serpentine conductive path may include a plurality of first longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of first transverse segments extending generally perpendicular to the first longitudinal segments, and the second serpentine conductive path may include a plurality of second longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of second transverse segments extending generally perpendicular to the second longitudinal segments. In such embodiments, at least some of the pairs of overlapping first and second segments include respective ones of the first and second lateral segments. In some embodiments, substantially all of the first lateral segments may overlap with respective ones of the second lateral segments. In some embodiments, in at least some of the pairs of overlapping first and second segments, one of the first and second segments may fully overlap the other of the first and second segments.

In some embodiments, the first serpentine conductive path and the second serpentine conductive path can each have a wave structure (e.g., sine wave, square wave, etc.). The frequency of the wave structure of the first serpentine conductive path may be different from the frequency of the wave structure of the second serpentine conductive path.

In some embodiments, the antenna may further include a third radiating element extending forward from the reflector, the third radiating element configured to operate in a third operating frequency band that includes higher frequencies than the second operating frequency band. The parasitic element may be configured to be substantially transparent to RF signals in the second operating frequency band and the third operating frequency band.

According to still other embodiments of the present invention, there is provided an antenna including: a first radiating element configured to operate in a first operating frequency band; a second radiating element configured to operate in a second operating frequency band that does not overlap the first frequency band and that includes a higher frequency than the first operating frequency band; and a parasitic element positioned adjacent to the first radiating element and the second radiating element, the parasitic element including a first conductive path having a wave structure with a first frequency and a second conductive path positioned behind the first conductive path having a wave structure with a second frequency, wherein the first frequency is different than the second frequency.

In some embodiments, the average width of the first conductive path may be less than 0.05 of a wavelength corresponding to a center frequency of the second operating frequency band, and the average width of the second conductive path may be less than 0.05 of a wavelength corresponding to a center frequency of the second operating frequency band.

In some embodiments, the first conductive path may include a plurality of first longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of first transverse segments extending generally perpendicular to the first longitudinal segments, and the second conductive path may include a plurality of second longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of second transverse segments extending generally perpendicular to the second longitudinal segments. At least some of the first lateral segments may overlap with respective ones of the second lateral segments. In some embodiments, substantially all of the first lateral segments may overlap with respective ones of the second lateral segments. In some embodiments, at least some of the first lateral segments may completely overlap with respective ones of the second lateral segments.

Any of the above antennas may include a pair of parasitic elements positioned on one side of the first radiating element of the antenna. Each of the pair of parasitic elements may include a first conductive path and a second conductive path positioned rearward of the first conductive path. The resonant frequency of the first parasitic element may be different from the resonant frequency of the second parasitic element such that the pair of parasitic elements together resonate over a larger portion of the operating frequency band of the first radiating element. In some embodiments, the resonant frequency of the first parasitic element may differ from the resonant frequency of the second parasitic element by at least 5%.

In some embodiments, two parasitic elements of the pair of parasitic elements may be implemented in a common printed circuit board. In some embodiments, two parasitic elements of the pair of parasitic elements may be stacked in a forward dimension of the antenna (i.e., stacked in a direction extending forward from a plane defined by a reflector of the antenna).

Drawings

Fig. 1 is a perspective view of a base station antenna according to an embodiment of the present invention.

Fig. 2 is a front view of the base station antenna of fig. 1 with the radome removed.

Fig. 3 is a cross-sectional view of the base station antenna of fig. 1 with the radome removed.

Fig. 4A is an enlarged perspective view of one of the low band radiating elements of the base station antenna of fig. 1-3.

Fig. 4B is a side view of the low band radiating element of fig. 4A.

Fig. 4C is a plan view of a dipole radiator printed circuit board of the low band radiating element of fig. 4A.

Fig. 4D is an exploded perspective view of one of the dipole arms included on the printed circuit board of the dipole radiator of fig. 4C.

Fig. 4E is an enlarged perspective view of portions of the first and second conductive serpentine included on each dipole arm of the low-band radiating element of fig. 4A.

Fig. 4F is an enlarged perspective view of the connection between one of the feed tangs and the base of one of the dipole arms of the low-band radiating element of fig. 4A.

Fig. 5A is a perspective view of a small portion of the first and second conductive paths of the low band radiating element of fig. 4A-4F showing the direction of current flow on the respective conductive paths in response to radiation emitted by a nearby mid band radiating element.

Fig. 5B is a perspective view of a small portion of the first and second conductive paths of the low band radiating element of fig. 4A-4F, showing the direction of low band current flow on the respective conductive paths.

Fig. 6-9 are perspective views of a small portion of a first conductive serpentine and a second conductive serpentine included on a dipole arm of a low-band radiating element according to further embodiments of the present invention.

Fig. 10 is a schematic front view of a dipole radiator printed circuit board of a low-band radiating element according to still other embodiments of the present invention.

Fig. 11 is a schematic perspective view of a conventional base station antenna including a linear array of low band radiating elements and associated parasitic elements positioned on either side of the linear array.

Fig. 12 is a schematic diagram showing how parasitic elements extending forward from the reflector of a base station antenna may be positioned around a radiating element to improve its cross-polarization discrimination performance.

Fig. 13A-13C are plan views of several conventional masking parasitic elements designed to resonate in the low-band cellular frequency band.

Fig. 14A is a plan view of a masking parasitic element in accordance with an embodiment of the present invention.

Fig. 14B is a perspective view of two metal patterns included in the masking parasitic element of fig. 14A.

Fig. 14C is a schematic side view of a portion of the masking parasitic element of fig. 14A.

Fig. 15 is a graph comparing the magnitude of the current induced on the conventional parasitic element of fig. 13A with the magnitude of the current induced on the parasitic element of fig. 14A-14C.

Fig. 16A and 16B are schematic plan views of a base station antenna including parasitic elements according to an embodiment of the present invention.

Fig. 17 is a schematic diagram showing four additional parasitic elements positioned around a radiating element in accordance with an embodiment of the present invention.

Fig. 18 is a plan view of a dual parasitic element including a pair of parasitic elements having different resonant frequencies implemented on a printed circuit board.

Detailed Description

Embodiments of the present invention generally relate to radiating elements for multi-band base station antennas and to related base station antennas. A multi-band base station antenna according to embodiments of the present invention may, for example, support three or more primary air interface standards in three or more cellular bands and allow a wireless carrier to reduce the number of antennas deployed at the base station, thereby reducing tower rental costs.

The challenge in multi-band base station antenna design is to reduce the effect of scattering RF signals in one frequency band by radiating elements of other frequency bands. Scattering is undesirable because it can affect the shape of the antenna beam in both the azimuth plane and elevation plane, and the effect can vary significantly with frequency, which can make it difficult to compensate for these effects. Furthermore, at least in the azimuth plane, scattering tends to affect beam width, beam shape, pointing angle, gain and front-to-back ratio in an undesirable manner. Radiating elements according to some embodiments of the present invention may be designed to have reduced impact (i.e., reduced scattering) on the antenna pattern of closely positioned radiating elements that transmit and receive signals in other frequency bands.

Masking low-band radiating elements is known in the art. For example, U.S. patent No. 9,570,804 discloses a low-band radiating element operating in the 696-960MHz band that includes dipole arms formed as a series of RF chokes to make the low-band radiating element substantially transparent to RF energy in the 1.7-2.7GHz band. U.S. patent No. 10,439,285 and U.S. patent No. 10,770,803 each disclose a low-band radiating element operating in the 696-960MHz band that includes dipole arms formed as a series of widened sections joined by narrow inductive sections that may be implemented as small serpentine trace sections on a printed circuit board. In each case, the narrow inductive segment acts as a high impedance element for RF energy in the 1.7-2.7GHz band, such that the low band radiating element is substantially transparent to RF energy in this frequency range. As another example, U.S. patent No. 11,018,437 discloses a low-band radiating element operating in the 696-960MHz band that includes two dipole arms that are substantially transparent to RF energy in the 1.7-2.7GHz band and two other dipole arms that are substantially transparent to RF energy in the 3.3-4.2GHz band. Additional masking radiating element designs are disclosed in chinese patent number CN 112787061a, chinese patent number CN 112164869a, chinese patent number CN 112290199a, chinese patent number CN 111555030a, chinese patent number CN 112186333a, chinese patent number CN 112186341a, chinese patent number CN 112768895A, chinese patent number CN 112821044A, chinese patent number CN 213304351U, and chinese patent number CN 112421219 a.

According to an embodiment of the present invention, a multi-band base station antenna is provided having a linear array of first, second and third radiating elements that transmit and receive signals in different respective first, second and third frequency bands. In some embodiments, the first frequency band may include 617-960MHz bands or portions thereof, the second frequency band may include 1427-2690MHz bands or portions thereof, and the third frequency band may include 3100-4200MHz bands or portions thereof. Each first radiating element may be a broadband decoupling radiating element having a dipole radiator that is substantially transparent to RF energy in both the second frequency band and the third frequency band. By providing a dipole radiator that is transparent to RF energy in two different frequency bands, it is possible, for example, to position a second radiating element operating in the second frequency band closely on one side of the first radiating element and a third radiating element operating in the third frequency band closely on the other side of the first radiating element without the first radiating element substantially affecting the antenna pattern formed by the second and third radiating elements. When the base station antenna according to the embodiment of the present invention includes the radiating element array operating in three different frequency bands, the radiating element operating in the lowest frequency band may be referred to as a "low-band" radiating element, the radiating element operating in the highest frequency band may be referred to as a "high-band" radiating element, and the radiating element operating in the middle frequency band may be referred to as a "middle-band" radiating element.

Base station antennas according to some embodiments of the present invention may include low-band radiating elements designed to be substantially transparent to RF energy emitted by mid-band and/or high-band radiating elements included in the antenna. These low band radiating elements may include a first dipole radiator and a second dipole radiator. The dipole radiators may be implemented in a "cross" arrangement to form a pair of center fed +/-45 ° dipole radiators, as is well known in the art. Each dipole arm may include a first stacked serpentine conductive path and a second stacked serpentine conductive path. For example, dipole arms may be formed on a printed circuit board (or multiple printed circuit boards), with a first serpentine conductive path of each dipole arm mounted on a first conductive layer of the printed circuit board and a second serpentine conductive path of each dipole arm mounted on a second, different conductive layer of the printed circuit board. Each serpentine conductive path may include a thin conductive trace having a length that is substantially longer than its width, wherein the conductive trace is a non-linear conductive trace that follows the serpentine path to increase its path length. In some embodiments, the total length of each serpentine conductive path (i.e., the sum of the lengths of each segment of the path) can be at least 75% longer than the straight line distance from the base of the serpentine conductive path to the distal end of the serpentine conductive path. In other embodiments, the total length of each serpentine conductive path can be at least twice or at least three times the linear distance from the base of the serpentine conductive path to the distal end of the serpentine conductive path.

In some embodiments, the first serpentine conductive path and the second serpentine conductive path each can have a wave shape, such as a generally square wave structure. The direction of effective current flow along each serpentine conductive path can be along a longitudinal axis of the serpentine conductive path (or along several longitudinal axes if the serpentine conductive path includes a bend that divides the serpentine conductive path into a plurality of sections). In some embodiments, each serpentine conductive path can include a longitudinal segment extending generally in a direction of effective current flow and a lateral segment extending generally in a direction perpendicular to the direction of effective current flow. At least some of the lateral segments of the first serpentine conductive path can "overlap" with corresponding ones of the lateral segments of the second serpentine conductive path to form a plurality of pairs of overlapping lateral segments. In this context, the first and second segments of the respective first and second conductive paths "overlap" if an axis perpendicular to a plane defined by the first segment (or a plane defined by portions of the reflector rearward of the first and second segments if the first segment does not define a single plane) passes through both the first and second segments.

As described above, these low-band radiating elements may have features that allow their dipole arms to pass low-band currents while suppressing the formation of currents in the mid-band and/or high-band frequency ranges in response to radiation emitted by nearby mid-band and/or high-band radiating elements. For example, the widths of the metal traces forming the first and second serpentine conductive paths may be selected such that low band currents may flow relatively freely on the serpentine conductive paths while mid-band and/or high band currents are substantially suppressed. The use of such narrow traces creates an inductive effect that appears to be high impedance to higher frequency RF signals, thereby suppressing the formation of current for such radiation, while having sufficiently low impedance to lower frequency RF signals. As another example, the length of each transverse segment (or the average length of the transverse segments) may be selected to be less than one-fourth of the wavelength corresponding to the lowest frequency RF signal to be suppressed (or alternatively, less than one-fourth of the wavelength corresponding to the center frequency of the operating band of the mid-band radiating element). This again facilitates suppression of mid-band and/or high-band currents without substantially affecting low-band currents.

As another example, the dipole arms may be designed such that for at least some of the pairs of overlapping lateral segments, the instantaneous direction of a first current formed on a first segment in response to mid-band and/or high-band RF radiation will be substantially opposite to the instantaneous direction of a second current formed on a second segment in response to such mid-band/high-band RF radiation. This tends to result in cancellation of any mid-band and/or high-band currents. The dipole arms may be designed such that the same effect is suppressed with respect to the low-band current, allowing the low-band current to flow freely on the dipole arms.

In one example embodiment of the invention, an antenna is provided that includes a reflector. First and second radiating elements configured to operate in respective first and second operating frequency bands extend forward from the reflector. The first radiating element may comprise a low-band radiating element, e.g. being part of an array of low-band radiating elements, and the second radiating element may comprise a mid-band radiating element, e.g. being part of an array of mid-band radiating elements, or a high-band radiating element being part of an array of high-band radiating elements. The first radiating element includes a first dipole radiator having a first dipole arm and a second dipole radiator having a third dipole arm and a fourth dipole arm. The first dipole arm includes a first conductive path and a second conductive path positioned behind the first conductive path, wherein the first conductive path includes a plurality of first segments and the second conductive path includes a plurality of second segments. A first segment of the subset of first segments overlaps a corresponding segment of a second segment of the subset of second segments to form a plurality of pairs of overlapping first and second segments. At least some of each pair of overlapping first and second segments are configured such that the instantaneous direction of a first current formed on the first segment in response to RF radiation emitted by the second radiating element will be substantially opposite to the instantaneous direction of a second current formed on the second segment in response to RF radiation emitted by the second radiating element.

In another example embodiment of the present invention, an antenna is provided that includes a reflector and first and second radiating elements extending forward from the reflector and operating in different frequency bands. The first radiating element includes a first dipole arm having a first spaced apart conductive path and a second spaced apart conductive path, wherein a first segment of the first conductive path overlaps a second segment of the second conductive path. The first dipole arms are configured such that first and second currents induced on respective first and second conductive paths in response to RF radiation emitted by the second radiating element each flow outwardly along the first dipole arms but in substantially opposite directions along respective first and second segments.

According to yet other embodiments of the present invention, a radiating element is provided that includes a first dipole radiator having a first pair of dipole arms and a second dipole radiator having a second pair of dipole arms. Each dipole arm includes a first serpentine conductive path extending from its base to its distal end and a second serpentine conductive path positioned rearward of the first serpentine conductive path.

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1-3 illustrate a base station antenna 100 according to some embodiments of the present invention. Specifically, fig. 1 is a perspective view of the antenna 100, while fig. 2 and 3 are front and cross-sectional views of the antenna 100, respectively, with its radome removed to show the antenna assembly 200 of the antenna 100.

In the following description, the following terms will be used to describe the antenna 100 and the radiating elements included therein, assuming that the antenna 100 is mounted on a tower for normal use, with the longitudinal axis of the antenna 100 extending along a vertical axis, and the front surface of the antenna 100 mounted opposite the tower directed toward the coverage area of the antenna 100.

As shown in fig. 1-3, the base station antenna 100 is an elongated structure extending along a longitudinal axis L. The base station antenna 100 may have a tubular shape with a substantially rectangular cross section. The antenna 100 includes a radome 110 and a tip cover 120. The antenna 100 also includes a bottom end cap 130 that includes a plurality of connectors 140, such as RF ports, mounted therein. When the antenna 100 is installed for normal operation, the antenna 100 is typically installed in a vertical configuration (i.e., the longitudinal axis L may be substantially perpendicular to a plane defined by the horizon). The radome 110, the top cover 120, and the bottom cover 130 may form an outer housing of the antenna 100. The antenna assembly 200 is contained within an outer housing. The antenna assembly 200 may be slidably inserted into the radome 110 from the top or bottom before the top cover 120 or the bottom cover 130 is attached to the radome 110.

Fig. 2 and 3 are front and cross-sectional views, respectively, of an antenna assembly 200 of the base station antenna 100. As shown in fig. 2 and 3, the antenna assembly 200 includes a ground plane structure 210 having sidewalls 212 and a reflector surface 214. Various mechanical and electrical components (not shown) of the antenna, such as phase shifters, remote electronic tilting units, mechanical linkages, controllers, diplexers, etc., may be mounted in the chamber defined between the side walls 212 and the backside of the reflector surface 214. The reflector surface 214 of the ground plane structure 210 may include or comprise a metal surface (e.g., aluminum sheet) that acts as a reflector and ground plane for the radiating elements of the antenna 100. The reflector surface 214 may also be referred to herein as a reflector 214.

A plurality of dual polarized radiating elements are mounted to extend forwardly from reflector 214 (in the views of fig. 2-3, the radiating elements extend upwardly from reflector 214, but it will be appreciated that when antenna 100 is mounted for normal use, the antenna assembly will be rotated approximately 90 deg. from the orientation shown in fig. 2-3). The radiating elements include a low band radiating element 224, a mid band radiating element 234, and high band radiating elements 244, 254. The low band radiating elements 224 are mounted in two columns to form two linear arrays 220-1, 220-2 of low band radiating elements 224. The mid-band radiating elements 234 may likewise be mounted in two columns to form two linear arrays 230-1, 230-2 of mid-band radiating elements 234. Two planar arrays of high-band radiating elements 244, 254 are included in the antenna 100. The first planar array 240 includes four columns 242 of high-band radiating elements 244. The second planar array 250 includes four columns 252 of high-band radiating elements 254. The high-band radiating element 244 may be the same as or different from the high-band radiating element 254. All four columns 242 of high-band radiating elements 244 may be coupled to ports of a first beamforming radio (not shown) such that the first planar array 240 may perform active beamforming to generate higher gain antenna beams. All four columns 252 of high band radiating elements 254 may be coupled to ports of a second beamforming radio (not shown) so that the second planar array 250 may perform active beamforming as well. It will be appreciated that the number of arrays of low band, mid band and/or high band radiating elements may be different from that shown in figures 2 and 3, as may the number of columns and/or the number of radiating elements in each array and the relative positions of the arrays. It should be noted that like elements herein may be referenced individually by their entire reference number (e.g., linear array 230-2) and may be referenced collectively by the first portion of their reference number (e.g., linear array 230).

In the depicted embodiment, the first and second planar arrays 240, 250 of high-band radiating elements 244, 254 are positioned between the linear arrays 220-1, 220-2 of low-band radiating elements 224, and each linear array 220 of low-band radiating elements 224 is positioned between a planar array 240, 250 of high-band radiating elements 244, 254 and a respective one of the linear arrays 230 of mid-band radiating elements 234. It should be appreciated that antenna 100 illustrates one typical layout of an array of low band radiating elements, mid band radiating elements, and high band radiating elements. Many other array configurations are commonly used based on application and customer requirements. Radiating elements according to embodiments of the present invention may be used in arrays having any suitable configuration.

The low band radiating element 224 may be configured to transmit and receive signals in a first frequency band. In some embodiments, the first frequency band may include a 617-960MHz frequency range or a portion thereof (e.g., 617-896MHz band, 696-960MHz band, etc.). The mid-band radiating element 234 may be configured to transmit and receive signals in a second frequency band. In some embodiments, the second frequency band may include the 1427-2690MHz frequency range or a portion thereof (e.g., 1710-2200MHz band, 2300-2690MHz band, etc.). The high-band radiating elements 244, 254 may be configured to transmit and receive signals in a third frequency band. In some embodiments, the third frequency band may include the 3300-4200MHz frequency range or a portion thereof. The low-band linear array 220 may or may not be configured to transmit and receive signals in the same portion of the first frequency band. For example, in one embodiment, the low band radiating elements 224 in the first linear array 220-1 may be configured to transmit and receive signals in the 700MHz band, and the low band radiating elements 224 in the second linear array 220-2 may be configured to transmit and receive signals in the 800MHz band. In other embodiments, the low-band radiating elements 224 in both the first and second linear arrays 220-1, 220-2 may be configured to transmit and receive signals in the same frequency band to support the use of multiple-input multiple-output ("MIMO") communication techniques. The mid-band radiating element 234 and the high-band radiating elements 244, 254 in the different mid-band arrays 230 and high-band arrays 240, 250 may similarly have any suitable configuration. The radiating elements 224, 234, 244, 254 may be dual polarized radiating elements, and thus each array 220, 230, 240, 250 may be used to form a pair of antenna beams, one for each of two polarizations where the dual polarized radiating elements are designed to transmit and receive RF signals.

Although not shown in the figures, the radiating elements 224, 234, 244, 254 may be mounted on a feeder board that couples RF signals to and from the respective radiating elements 224, 234, 244, 254. One or more radiating elements 224, 234, 244, 254 may be mounted on each feeder plate. Cables may be used to connect each feeder board to other components of the antenna, such as a diplexer, phase shifter, and the like.

While cellular network operators are interested in deploying antennas with a large number of radiating element arrays in order to reduce the number of base station antennas required for each base station, increasing the number of arrays generally increases the width of the antennas. Both the weight and wind load of a base station antenna increase with increasing width, so a wider base station antenna tends to require a more structurally stable antenna mast and antenna tower, both of which can significantly increase the cost of the base station. Thus, the cellular network operator may impose a limit on the width of the base station antenna (where the limit may depend on the application of the antenna). For example, for many applications, cellular network operators may require base station antennas to be less than 500mm wide. This can be challenging in a base station antenna comprising two linear arrays of low band radiating elements, as most conventional low band radiating elements designed to serve 120 ° sectors have a width of about 200mm or more.

The width of the multi-band base station antenna may be reduced by reducing the spacing between adjacent arrays. However, as the spacing decreases, the coupling between the radiating elements of the different arrays increases, and such coupling increases may affect the shape of the antenna beam produced by the arrays in an undesirable manner. For example, low-band cross-dipole radiating elements typically have a dipole radiator of approximately 1/2 wavelength of the center frequency of the design operating band of the radiating element. If the low band radiating element is designed to operate in the 700MHz band and the mid band radiating element is designed to operate in the 1400MHz band, the length of the low band dipole radiator will be approximately one wavelength of the mid band operating frequency. Thus, each dipole arm of the low-band dipole radiator has a length of about 1/2 wavelength of the mid-band operating frequency, and therefore RF energy transmitted by the mid-band radiating element will tend to couple to the low-band radiating element because this RF energy will resonate in the 1/2 wavelength dipole arm.

When mid-band and/or high-band RF energy is coupled to the dipole arms of the low-band radiating elements, mid-band and/or high-band currents are induced on the dipole arms. Such induced currents are particularly likely to occur when the low-band radiating element and the mid-band radiating element are designed to operate in frequency bands having center frequencies that are about twice (or four times) apart, because a low-band dipole arm that is one-quarter wavelength in length at the low-band operating frequency will in this case have a length that is about one-half wavelength (or full wavelength) at the higher-band operating frequency. The induced current produces mid-band and/or high-band RF radiation emitted from the low-band dipole arms. The mid-band/high-band RF energy emitted from the dipole arms of the low-band resonating element distorts the antenna beam of the mid-band and/or high-band array because the radiation is emitted from a different location than intended. The greater the extent to which mid-band/high-band currents are induced on the low-band dipole arms, the greater the impact on the characteristics of the antenna beams produced by the mid-band array and the high-band array.

The low band radiating element 224 according to an embodiment of the present invention may be designed to be substantially transparent to RF energy emitted by the mid band radiating element 234 and the high band radiating elements 244, 254. Thus, even if the mid-band radiating element 234 and the high-band radiating elements 244, 254 are in close proximity to the low-band radiating element 224, the undesirable coupling of mid-band and/or high-band RF energy to the low-band radiating element 224, discussed above, may be significantly reduced.

Fig. 4A-4F illustrate a low band radiating element 300 that may be used to implement the low band radiating element 224 of the base station antenna 100 in accordance with an embodiment of the present invention. In particular, fig. 4A and 4B are an enlarged perspective view and a side view, respectively, of the low-band radiating element 300. Fig. 4C is a plan view of a dipole radiator printed circuit board 320 that is part of the low band radiating element 300. Fig. 4D is an exploded perspective view of one of the dipole arms of the low-band radiating element 300. Fig. 4E is an enlarged perspective view of portions of the first and second conductive serpentine included on each dipole arm of the low-band radiating element 300. Fig. 4F is an enlarged perspective view of the connection between one of the feed tangs of the low-band radiating element 300 and the base of one of the dipole arms.

Referring to fig. 4A-4C, the low band radiating element 300 includes a pair of feed handles 310 and a dipole radiator printed circuit board 320. A first dipole radiator 322-1 and a second dipole radiator 322-2 are formed on the dipole radiator printed circuit board 320. The first dipole radiator 322-1 includes a first dipole arm 330-1 and a second dipole arm 330-2, and the second dipole radiator 322-2 includes a third dipole arm 330-3 and a fourth dipole arm 330-4. The dipole radiators 322-1, 322-2 may be implemented in a "cross" arrangement to form a pair of center fed +/-45 ° dipole radiators 322.

The feed handles 310 may each include a printed circuit board 312 having an RF transmission line 314 formed thereon. These RF transmission lines 314 carry RF signals between a feed line board (not shown) mounted on the reflector 214 and the dipole radiator 322. Each feed handle 310 may also include a hook-shaped balun (hook balun) 316. A first one of the feed pins 310-1 may include a front slit and a second one of the feed pins 310-2 may include a rear slit. These slots allow the two feed handles 310 to be assembled together to form a forwardly extending post having a generally x-shaped vertical cross section. The rear portion of each feed handle 310 may include a protrusion that is inserted through a slot in a feed plate (not shown) to mount the radiating element 300 thereto. The RF transmission line 314 on the respective feed handle 310 may center feed the dipole radiators 322-1, 322-2.

The azimuth half-power beamwidth of each low-band radiating element 300 may be in the range of 55 degrees to 85 degrees. In some embodiments, the azimuthal half-power beamwidth of each low-band radiating element 300 may be approximately 65 degrees in the center of the operating band of the low-band radiating element 300.

The length of each dipole arm 330 may be an operating wavelength of about 0.2 to 0.35, where "operating wavelength" refers to a wavelength corresponding to the center frequency of the operating band of the radiating element 300. For example, if the low band radiating element 300 is designed to transmit and receive signals spanning the 694-960MHz band, then the center frequency of the operating band will be 827MHz with a corresponding operating wavelength of 36.25cm.

The dipole radiator printed circuit board 320 includes a dielectric substrate 326 having a first conductive layer 324 formed on a front side thereof and a second conductive layer 328 formed on a rear side thereof, as best shown in fig. 4D. In an example embodiment, the conductive layers 324, 328 may include a patterned copper layer, and may be referred to herein as a "metal layer. The dipole radiator printed circuit board 320 can also include a protective dielectric coating (not shown) on the front side and/or the back side of the dielectric substrate 326 that covers and protects the first metal layer 324 and the second metal layer 328. The metal pattern in the metal layers 324, 328 forms dipole arms 330. The first metal layer 324 may define a first plane and the second metal layer 328 may define a second plane parallel to and spaced apart from the first plane. In some embodiments, both the first plane and the second plane may be substantially parallel to the plane defined by the reflector 214. Each feed handle 310 may extend in a direction substantially perpendicular to the first plane and the second plane.

As best shown in fig. 4C, the first dipole radiator 322-1 extends along a first axis and the second dipole radiator 322-2 extends along a second axis that is substantially perpendicular to the first axis 322-1. Accordingly, the first and second dipole radiators 322-1 and 322-2 are arranged in a substantially cross shape. The dipole arms 330-1 and 330-2 of the first dipole radiator 322-1 are center fed by the first RF transmission line 314-1 and radiate together at a first polarization (see fig. 4A). In the depicted embodiment, the first dipole radiator 322-1 is designed to emit a signal having a polarization of-45 degrees. The dipole arms 330-3 and 330-4 of the second dipole radiator 322-2 are center fed by the second RF transmission line 314-2 and radiate together at a second polarization orthogonal to the first polarization. The second dipole radiator 322-2 is designed to transmit signals having a +45° polarization. Dipole arm 330 may be mounted at about 3/16 to 1/4 of the operating wavelength in front of reflector 214 by feed handle 310.

Referring again to fig. 2 and 3, it can be seen that the low band radiating element 224 (300) extends farther forward from the reflector 214 than both the mid band radiating element 234 and the high band radiating elements 244, 254. In order to keep the width of the base station antenna 100 relatively narrow, the low band radiating element 224 (300) may be positioned very close to both the mid band radiating element 234 and the high band radiating elements 244, 254. In the depicted embodiment, each low-band radiating element 224 (300) of the linear array 230 adjacent to the mid-band radiating element 234 may overlap a majority of two of the mid-band radiating elements 234. Likewise, each low-band radiating element 224 (300) adjacent to an array 240, 250 of high-band radiating elements 244, 254 may overlap at least a portion of one or more of the high-band radiating elements 244, 254. This arrangement allows the width of the base station antenna 100 to be significantly reduced. As discussed above, herein, first and second segments of respective first and second conductive paths "overlap" if an axis perpendicular to a plane defined by the first segment (or a plane defined by portions of the reflector rearward of the first and second segments) passes through both the first and second segments.

While positioning the low-band radiating element 224 (300) such that it overlaps the mid-band radiating element 234 and/or the high-band radiating elements 244, 254 may advantageously facilitate reducing the width of the base station antenna 100, this approach may significantly increase the coupling of RF energy emitted by the mid-band radiating element 234 and/or the high-band radiating elements 244, 254 onto the low-band radiating element 224 (300), and such coupling may reduce the antenna pattern formed by the array 230 of mid-band radiating elements 234 and/or the array 240, 250 of high-band radiating elements 244, 254.

To reduce this coupling, the low-band radiating element 300 may be designed with dipole arms 330 that are substantially "transparent" to the radiation emitted by both the mid-band radiating element 234 and the high-band radiating elements 244, 254. This can be challenging because the mid-band radiating element 234 can (in some cases) operate at frequencies as low as 1427MHz, and the high-band radiating elements 244, 254 can (in some cases) operate at frequencies as high as 4200 MHz. Thus, desirably, the low band radiating element 300 is substantially transparent to RF energy in the 1427-4200MHz frequency range, while allowing current in the 617-960MHz frequency range to flow freely on the dipole arms 330. Herein, if RF energy in a second frequency band is poorly coupled to a dipole arm, the dipole arm of a radiating element configured to emit RF energy in a first frequency band is considered "transparent" to RF energy in a second, different frequency band RF energy. Thus, if the dipole arms of the first radiating element transparent to the second frequency band are positioned such that they overlap the second radiating element that is emitted in the second frequency band, then adding the first radiating element will not substantially affect the antenna pattern of the second radiating element.

Referring to fig. 4C and 4D, each dipole arm 330 includes a first conductive path 340 implemented in the first metal layer 324 of the dipole radiator printed circuit board 320 and a second conductive path 350 implemented in the second metal layer 328 of the dipole radiator printed circuit board 320. The second conductive path 350 is positioned behind the first conductive path 340. The first conductive path 340 and the second conductive path 350 may each comprise a respective serpentine conductive path. Here, a serpentine conductive path refers to a nonlinear conductive path that follows a serpentine path to increase its path length. The conductive path may comprise a thin conductive trace having a length that is much longer than its width. The use of serpentine conductive paths allows the length of the paths to be significantly increased while still providing relatively compact first 340 and second 350 conductive paths. Examples of serpentine conductive paths are conductive paths having the general form of square waves or sine waves, but embodiments of the present invention are not limited thereto. It should also be appreciated that if the serpentine conductive path is formed to have a wave shape (e.g., a square wave), the magnitude and/or frequency of the wave need not be constant.

As shown in fig. 4C-4D, in an exemplary embodiment, the first conductive path 340 and the second conductive path 350 may each have a general form of a square wave that is "bent" into a closed loop shape such that each dipole arm 330 has a generally oval shape. To form a closed loop shape, each serpentine conductive path 340, 350 is divided into a plurality of sections 342, 352, wherein the serpentine conductive paths 340, 350 extend along respective longitudinal axes 344, 354, and the sections 342, 352 (and thus the longitudinal axes 344, 354) are angled relative to each other. The longitudinal axes 344, 354 are shown in fig. 4C with respect to dipole arm 330-4. Because each section 342 of the serpentine conductive path 340 extends in the same direction as the corresponding section 352 of the serpentine conductive path 350, the axes 344 and 354 are the same axis in plan view and are thus shown as a single axis 344/354 in fig. 4C. For example, a first section 342-1 of a first serpentine conductive path 340 is interposed between a base 331 of a dipole arm 330-1 and a second section 342-2 of the first serpentine conductive path 340, and a first section 352-1 of a second serpentine conductive path 350 is interposed between the base 331 of the dipole arm 330-1 and the second section 352-2 of the second serpentine conductive path 350. The first sections 342-1, 352-1 are angled at a first angle α relative to the respective second sections 342-2, 352-2. In the depicted embodiment, each serpentine conductive path 340, 350 includes a total of six sections 342-1 through 342-6. The base 331 of each dipole arm 330 (and the bases forming the conductive paths 340, 350 of the dipole arms 330) is adjacent the center of the radiating element 300. The distal end 339 of each dipole arm 330 is the outermost portion of the respective dipole arm 330. As shown, the third section 342-3 and the fourth section 342-4 of the dipole arm 330-1 may be connected to each other at the distal end 339 of the dipole arm 330-1 such that the dipole arm 330 may include a pair of closed loop structures. In other embodiments, the third section 342-3 and the fourth section 342-4 of the dipole arm 330-1 may not be connected to each other. The direction of the effective current flow of the low-band current along each serpentine conductive path 340, 350 may be along the longitudinal axis 344, 354 of each section 342, 352 of the serpentine conductive path 340, 350.

Fig. 4E is an enlarged view of a portion of the respective sections 342, 352 of the first and second serpentine conductive paths 340, 350. As can be seen, the first serpentine conductive path 340 includes a plurality of first longitudinal segments 346 extending generally parallel to the longitudinal axis 344 of the segment 342, and a plurality of first transverse segments 348 extending generally perpendicular to the longitudinal axis 344 of the segment 342. Likewise, the second serpentine conductive path 350 includes a plurality of second longitudinal segments 356 extending generally parallel to the longitudinal axis 354 of the segment 352 and a plurality of second transverse segments 358 extending generally perpendicular to the longitudinal axis 354 of the segment 352. On each conductive path 340, 350, the longitudinal sections 346 and the transverse sections 348 alternate to form square waves.

As can be seen from fig. 4E, at least some of the first transverse segments 348 overlap respective ones of the second transverse segments 358 to form a plurality of pairs 360 of overlapping first and second transverse segments 348, 358. As described above, if an axis perpendicular to the plane defined by the first segment passes through both the first segment and the second segment, the first segment and the second segment of the conductive path (e.g., the first transverse segment 348 and the second transverse segment 358) are "overlapped. In the depicted embodiment, the second serpentine conductive path 350 defines a square wave having a frequency that is twice the frequency of the square wave defined by the first serpentine conductive path 340. Thus, each first transverse segment 348 of the first serpentine conductive path 340 overlaps a corresponding second transverse segment 358 of the second serpentine conductive path 350, but only half of the second transverse segments 358 have corresponding overlapping first transverse conductive segments 348.

The overlapping first and second transverse segments 348, 358 of each pair 360 may be configured to help inhibit the formation of currents on the first and second serpentine conductive paths 340, 350 in response to RF radiation emitted by the mid-band radiating element 234 or the high-band radiating elements 244, 254, which may be positioned adjacent to the low-band radiating element 300. In particular, each pair 360 of overlapping first and second lateral segments 348, 358 may be configured such that the instantaneous direction of the first current formed on the first lateral segment 348 of the pair 360 in response to RF radiation emitted by the mid-band radiating element 234 or the high-band radiating elements 244, 254 will be substantially opposite to the instantaneous direction of the second current formed on the second lateral segment 358 of the pair 360 in response to mid-band or high-band RF radiation. Thus, the first and second currents "flowing" on the first and second transverse segments 348, 358 of each pair 360 of overlapping first and second transverse segments 348, 358 will tend to cancel each other, thereby inhibiting the formation of currents on the low band dipole arms 330 in response to RF radiation emitted by the nearby mid band radiating elements 234 or high band radiating elements 244, 254.

The low-band radiating element 300 may have features that allow its dipole arms 330 to pass low-band currents while suppressing currents in the mid-band and/or high-band frequency ranges that are formed in response to radiation emitted by the nearby mid-band 234 and/or high-band radiating elements 244, 254. For example, the width w (see fig. 4E) of the metal traces forming the serpentine conductive paths 340, 350 may be selected such that low-band currents may flow relatively freely on the serpentine conductive paths 340, 350 while mid-band and/or high-band currents are substantially suppressed. In some embodiments, the width w of each serpentine conductive path 340, 350 can be selected to be, for example, less than 0.05, which corresponds to the wavelength of the lowest frequency RF signal to be suppressed. The use of conductive traces with narrow widths creates an inductive effect that appears as a high impedance to higher frequency RF signals, thereby suppressing the formation of current from such radiation, while having a sufficiently low impedance to lower frequency RF signals (allowing current generated by such lower frequency RF signals to flow on dipole arms 330). In effect, the serpentine conductive paths 340, 350 form an inductance-capacitance (LC) resonant circuit. By selecting an appropriate width for the traces forming the serpentine conductive paths 340, 350, the LC circuit can appear as an open circuit at its resonant frequency, which can be at mid/high band frequencies. Accordingly, dipole arms 330 may tend to allow low-band currents to flow thereon while suppressing the formation of mid-band and high-band currents. The suppression will tend to increase with increasing frequency.

As another example, the "length" of each transverse segment 348, 358 (i.e., the distance that the transverse segments 348, 358 extend along their longitudinal axes) or, alternatively, the average length of all transverse segments on a given conductive path may be selected to be less than one-fourth of the wavelength corresponding to the lowest frequency RF signal to be suppressed. Thus, for example, in an exemplary embodiment, the length of each transverse segment 348, 358 (or the average length of the transverse segments 348, 358 on each conductive path 340, 350) may be selected to be less than one-fourth of the wavelength corresponding to 1427MHz frequency or 1690MHz frequency (the exemplary lowest frequency of the operating band of the mid-band radiating element 234). In other embodiments, the average length of the transverse segment 348 on the first serpentine conductive path 340 and the average length of the transverse segment 358 on the second serpentine conductive path 350 can each be less than 1/4 of a wavelength corresponding to the center frequency of the operating frequency band of the mid-band radiating element 234.

As another example, the dipole arms 330 can be designed such that for at least some of the pairs 360 of overlapping transverse segments, the direction of instantaneous current flow on the transverse segment 348 of the first serpentine conductive path 340 is substantially opposite to the direction of instantaneous current flow on the transverse segment 358 of the second serpentine conductive path 350. This tends to result in cancellation of any mid-band and/or high-band currents, but has only a very limited cancellation effect for low-band currents. This can best be seen with reference to fig. 5A-5B, which are perspective views of a small portion of the first serpentine conductive path 340 and the second serpentine conductive path 350 of the dipole arm 330-1, showing the direction of instantaneous current flow on the respective conductive paths for mid-band currents induced on the dipole arm 330-1 in response to RF radiation emitted by the nearby mid-band radiating element 234 (fig. 5A) and for low-band currents fed to the dipole arm 330-1 (fig. 5B).

As shown in fig. 5A, with respect to the induced mid-band current, the general direction of current flow on the first serpentine conductive path 340 is from right to left, or in the direction of the longitudinal axis 344 of the delineated section 342 of the first serpentine conductive path 340. Likewise, the general direction of current flow on the second serpentine conductive path 350 is from right to left, or in the direction of the longitudinal axis 354 of the depicted section 352 of the second serpentine conductive path 350. Thus, the current flow on the longitudinal sections 346, 356 of the respective first and second serpentine conductive paths 340, 350 is substantially parallel to the respective longitudinal axes 344, 354. The lateral conductive segments 348, 358 are configured such that the current flow on each lateral segment 348, 358 alternates from top to bottom and bottom to top of the lateral segments 348, 358. Since the square wave of the second serpentine conductive path 350 has a frequency that is twice the frequency of the square wave of the first serpentine conductive path 340, the direction of instantaneous current flow on each second lateral segment 358 can be substantially opposite to the direction of instantaneous current flow on the first lateral segment 348 of each pair 360 for each pair 360 of overlapping first and second lateral segments 348, 358. As discussed above, this results in the mid-band current and/or the high-band current tending to cancel each other, thereby inhibiting mid-band current and high-band current flow on dipole arm 330.

As shown in fig. 5B, low-band currents formed on dipole arms 330 tend to flow outwardly along dipole arms 330 when radiating element 300 is driven (i.e., fed with low-band RF signals). In the exemplary embodiment shown, the low-band currents flowing on each pair 360 of overlapping first and second lateral segments 348, 358 may have substantially the same instantaneous current direction, and thus no cancellation occurs. It can also be seen from fig. 5B that the low-band current flowing on the remaining pairs 360 of overlapping first and second lateral segments 348, 358 may have substantially opposite instantaneous current directions. However, even this produces the most limited current cancellation for low-band currents, because for low-band currents, the transverse segments 348, 358 have an orientation that is perpendicular to the polarization direction of the dipole arm (which is-45 ° direction for dipole arm 330-1) on average. Furthermore, when the lateral segments are positioned such that the average current flow thereon is perpendicular to the polarization direction of the dipole arms, the opposing currents tend not to cause the above-mentioned cancellation. Regarding low-band currents generated in response to a feed signal being supplied to the dipole arms, the currents flow outwardly on the dipole arms such that, on average, the current flow on the transverse segments is perpendicular to the polarization direction of the dipole arms. Thus, while suppressing mid-band and high-band currents, the design of the lateral segments 348, 358 on the dipole arms 330 may tend to have little effect on the low-band currents.

Fig. 4F is an enlarged perspective view of the connection between one of the feed handles 310 of the low-band radiating element 300 and the base 331 of the dipole arm 330-1. As can be seen in fig. 4F, the base end of the first serpentine conductive path 340 may include a generally rectangular metal pad 341 formed in the first metal layer 324 of the printed circuit board 320. Rectangular slots 333 are cut through the dipole radiator printed circuit board 320 within the generally rectangular metal pads 341. The tab 315 on the feed handle 310 is inserted through the rectangular slot 333. The transmission line 314 on the feed handle 310 extends to the front end of the feed handle 310 such that the transmission line 314 extends through the rectangular slot 333. One or more solder joints are formed on the front and/or rear surfaces of the base of the dipole arm 330-1 that electrically connect the transmission line 314 on the feed handle 310 to the generally rectangular metal pad 341 that forms the base of the first serpentine conductive path 340. One or more solder joints may also facilitate mechanical mounting of the dipole radiator printed circuit board 320 on the feed handle 310.

As can also be seen in fig. 4E-4F, a plurality of conductive vias 325 are formed through the dielectric substrate 326 of the dipole radiator printed circuit board 320. Conductive via 325 may include a metallization and/or a metal filled via. The generally rectangular metal pad 341 overlaps, and is thus electrically connected to, the conductive via 325. Likewise, a first one of the second lateral sections 358 of the first section 352-1 (and a first one of the second lateral sections 358 of the first section 352-6) overlaps and is thus electrically connected to the conductive via 325. Thus, both the first serpentine conductive path 340 and the second serpentine conductive path 350 are galvanically connected to the feed line 314 on the feed handle 310.

Fig. 6-9 are perspective views of a small portion of a first conductive serpentine conductive path and a second conductive serpentine conductive path included on dipole arms of a low band radiating element according to further embodiments of the present invention. Although only a small portion of one dipole arm is shown in fig. 6-9, it should be appreciated that the serpentine conductive path design shown in fig. 6-9 may be used in place of serpentine conductive paths 340, 350 in each dipole arm of radiating element 330 to provide additional low-band radiating elements in accordance with embodiments of the present invention.

Referring to fig. 6, a dipole arm 430 according to further embodiments of the present invention includes a first serpentine conductive path 440 spaced apart from a second serpentine conductive path 450 in the manner discussed above with respect to dipole arm 330. The first serpentine conductive path 440 is very similar to the first serpentine conductive path 340 described above, but at least some of the lateral segments 448 of the first serpentine conductive path 440 are widened lateral segments 448' (i.e., they extend further along the longitudinal axis 444 of the illustrated section of the dipole arm 430). This may advantageously increase the coupling between the current flowing in a first direction on the first serpentine conductive path 440 and the current flowing in a second opposite direction on the second serpentine conductive path 450, resulting in an increase in cancellation. Since all other aspects of the dipole arm 440 may be identical to the dipole arm 330 described above, a further description of the dipole arm 430 or its operation will be omitted.

Referring to fig. 7, a dipole arm 530 according to a further embodiment of the present invention includes a first serpentine conductive path 540 spaced apart from a second serpentine conductive path 550. The first and second serpentine conductive paths 540, 550 are similar to the respective first and second serpentine conductive paths 340, 350 described above, but the "magnitude" of the square wave formed by each serpentine conductive path 540, 550 is not constant, but varies. In the depicted embodiment, a first portion of the square wave has a magnitude M1 and the other portions have a magnitude M2, where the magnitudes correspond to the lengths of the transverse segments 548, 558 of the first and second serpentine conductive paths 540, 550. Although in fig. 7, the magnitude of each section of the first serpentine conductive path 540 is shown as being the same as the magnitude of each section of the second serpentine conductive path 550 that overlaps a corresponding section of the first serpentine conductive path 540, it should be appreciated that embodiments of the present invention are not so limited. Since all other aspects of the dipole arm 530 may be identical to the dipole arm 330 described above, a further description of the dipole arm 530 or its operation will be omitted.

Referring to fig. 8, a dipole arm 630 according to a further embodiment of the invention includes a first serpentine conductive path 640 spaced apart from a second serpentine conductive path 650. The first and second serpentine conductive paths 640, 650 are similar to the respective first and second serpentine conductive paths 340, 350 of the dipole arm 330 described above, but the ratio of the frequency of the square wave defined by the second serpentine conductive path 650 to the frequency of the square wave defined by the first serpentine conductive path 640 is 3:1 in the dipole arm 630, as compared to 2:1 in the dipole arm 330. For radiating elements having different operating bands, different frequency ratios may be more optimal. Since all other aspects of the dipole arm 630 may be identical to the dipole arm 330 described above, a further description of the dipole arm 630 or its operation will be omitted. It should be appreciated that in other embodiments, the ratio of the frequency of the wave defined by the second serpentine conductive path on the dipole arm to the frequency of the wave defined by the first serpentine conductive path on the dipole arm may take other values, such as 1:1, 4:1, 2.5:1, etc.

Referring to fig. 9, a dipole arm 730 according to further embodiments of the present invention includes only a first serpentine conductive path 740 and does not include any second serpentine conductive path. The inductance of the first serpentine conductive path 740 can be selected to suppress mid-band and/or high-band currents while allowing low-band currents to flow freely on the dipole arms 730.

It will also be appreciated that low band radiating elements according to embodiments of the present invention are not limited to dipole arms having the shape of dipole arm 330. Rather, the dipole arms may have any suitable shape, such as a linear shape, a circular shape, an oval shape, a square shape, and the like. For example, fig. 10 is a schematic front view of a dipole arm 830 of a low-band radiating element 800 having a linear shape of dipole arms each with a first serpentine conductive path 840 and a second serpentine conductive path 850 extending along a single longitudinal axis 844/854, in accordance with further embodiments of the present invention.

While the dipole arms of the low-band radiating elements described above are implemented on one or more dipole radiator printed circuit boards, it should be appreciated that embodiments of the present invention are not so limited. For example, in other embodiments, any of the radiating elements described above may be implemented using a sheet metal dipole arm mounted on a dielectric support. In such embodiments, the first and second serpentine conductive paths of each of the radiating elements described above may be formed by stamping appropriately shaped structures from sheet metal. The first serpentine conductive path and the second serpentine conductive path formed of the metal plate may then be mounted on opposite sides of the dielectric substrate to form each dipole arm. U.S. patent publication 2020/0161748 ("the' 748 publication") describes a technique for implementing a dipole arm as a metal plate on a plastic dipole arm. Any of the dipole arms disclosed herein may be implemented using a metal plate on the dielectric design disclosed in the' 748 publication, with a metal plate pattern having respective first and second conductive paths implemented on either side of a dielectric (e.g., plastic) support. The entire contents of the' 748 publication are incorporated herein by reference.

So-called "parasitic elements" are commonly used in base station antennas to improve the performance of an associated array of radiating elements included in the antenna. Parasitic element refers to a structure comprising one or more conductive patterns that are not coupled to a feed network of an associated radiating element array. The parasitic elements are used to alter the radiation pattern or "antenna beam" generated by the associated radiating element array in a desired manner.

The parasitic element is typically mounted in front of the reflector of the base station antenna, adjacent to the radiating element of the associated radiating element array. The parasitic elements are typically designed to resonate in the operating frequency band of the associated radiating element array such that RF energy emitted by the radiating element will induce currents on the parasitic elements and these currents cause the parasitic elements to re-radiate the received RF energy. The parasitic element may, for example, have an electrical length between a quarter and half of a wavelength corresponding to a center frequency of an operating frequency band of the associated radiating element array. The parasitic element is typically formed from a metal plate or using a printed circuit board, but other implementations are possible.

Parasitic elements are typically used to narrow the azimuth beamwidth of an antenna beam formed by a linear array of associated radiating elements. To achieve this, the first and second columns of parasitic elements may be mounted, for example, along either side of the linear array of associated radiating elements (i.e., each column of parasitic elements extends in a longitudinal direction and thus parallel to the longitudinal axis of the base station antenna). RF energy transmitted by an associated radiating element array that is transmitted at a relatively large azimuth angle may be incident on and induce a current on the parasitic element. These currents cause the parasitic element to radiate RF energy. The parasitic elements are positioned such that RF energy radiated from the parasitic elements is directed primarily toward the boresight of the associated radiating element array, thereby focusing the antenna beam in the azimuth plane. The parasitic elements may be designed such that the redirected RF energy is substantially constructively combined with RF energy emitted by the radiating element array at a smaller azimuth angle. In general, the parasitic elements allow a base station antenna manufacturer to use smaller radiating elements while still achieving a desired azimuth beamwidth performance for the antenna beam generated by the array of these smaller radiating elements.

When the parasitic element is used to narrow the azimuth beamwidth of the antenna beam generated by the linear array in the manner discussed above, the parasitic element is typically mounted in front of the reflector and extends parallel to the longitudinal axis of the base station antenna. Fig. 11 is a schematic perspective view of several low-band radiating elements 924 of a linear array 920 of low-band radiating elements 924 included in a conventional base station antenna 900, which shows how parasitic elements 952 may be positioned on either side of each radiating element 924 in order to reduce the azimuth beamwidth of the antenna beam generated by the linear array 920. Since the low band radiating element (typically operating in all or part of the 617-960MHz band) is typically the largest radiating element in a base station antenna, parasitic elements designed to reduce the azimuth beamwidth of the radiating element array are typically used in combination with the low band array of radiating elements (since low band radiating elements typically have the greatest impact on the overall size of the base station antenna).

Parasitic elements may also be used, for example, to improve cross-polarization discrimination of an array of radiating elements. This is especially true with respect to multi-column arrays of radiating elements used in beamforming antennas. When an antenna beam generated by such an array is scanned (typically in the azimuth plane) to a large scan angle, the cross-polarization discrimination of the array typically decreases (meaning that the amount of RF energy transmitted at a first polarization that is converted to a second orthogonal polarization increases). Parasitic elements extending forward from the reflector may be mounted around the radiating elements of such an array in order to improve the cross-polarization discrimination performance of the array. Fig. 12 is a schematic diagram showing how a parasitic element 1052 extending forward from reflector 1010 (i.e., the longitudinal axis of parasitic element 1052 is perpendicular to reflector 1010) may be positioned around a radiating element 1024 (e.g., a radiating element of a multi-column beamforming array of radiating elements) in order to improve its cross-polarization discrimination performance.

One potential difficulty that arises when adding parasitic elements to a base station antenna is that the parasitic elements may affect the antenna beams of more than one array of radiating elements. For example, many base station antennas include a vertically extending linear array of low band radiating elements and a pair of vertically extending linear arrays of mid band radiating elements mounted on either side of the low band array. To keep the width of such base station antennas small, each mid-band linear array may be positioned very close to the low-band array. Due to this close spacing, at least some of the mid-band radiating elements may be mounted "below" the low-band radiating elements, which means that for at least some of the mid-band radiating elements, an axis of the reflector perpendicular to the base station antenna extends through one of the mid-band radiating elements and the low-band radiating elements. Herein, when this condition is met, the low band radiating element may be said to "overlap" with the mid band radiating element. In other base station antennas, the radiating elements of the low band array may overlap with the radiating elements of the high band array, or may overlap with the radiating elements of both the mid band array and the high band array.

When the radiating elements of different arrays overlap or are otherwise in close proximity as described above, parasitic elements positioned proximate to the first array of radiating elements are also typically proximate to one or more additional arrays of radiating elements. Further, the low, medium and high frequency band frequency ranges include frequencies that differ by a factor of two or four, which means that parasitic elements resonating in one of the low, medium and high frequency bands typically resonate in the other of the low, medium and high frequency bands. For example, a parasitic element having an electrical length of one quarter wavelength at 900MHz will have an electrical length of one half wavelength at 1800MHz and an electrical length of one wavelength at 3600 MHz. Notably, 900MHz is in the low band cellular frequency range, 1800MHz is in the mid band cellular frequency range, and 3600MHz is in the high band cellular frequency range. Thus, the parasitic element described above may resonate in all three frequency bands and, thus, will tend to affect the antenna beam of any low, mid and high band array in close proximity to the parasitic element.

In practice, it may be difficult to design and position the parasitic element such that it improves the shape of the antenna beam generated by the nearby radiating element array operating in a different frequency band. To address this problem, so-called "masking" parasitic elements have been developed. Masking a parasitic element refers to a parasitic element that is designed to resonate in the operating frequency band of a first array of radiating elements, but is designed to be substantially transparent to RF energy in the operating frequency band of a second array of radiating elements. This ensures that the parasitic element only substantially affects the antenna beam generated by the first array of radiating elements.

Fig. 13A-13C are plan views of several conventional masking parasitic elements 1152A, 1152B, 1152C that are designed to resonate in the low-band cellular frequency band while being substantially transparent to RF energy in the higher-band. Each of these parasitic elements 1152A, 1152B, 1152C is implemented using a printed circuit board having a metal pattern on one side thereof. The metal patterns of parasitic elements 1152A, 1152B, 1152C are each implemented as a dipole comprising a plurality of widened conductive segments 1154 electrically connected in series by a plurality of narrow conductive segments 1156. By appropriately sizing the widened conducting segments 1154 and the narrow conducting segments 1156, the dipole can be made substantially transparent to RF energy in the higher frequency band. In effect, the fringe capacitance between adjacent widened conducting segments 1154 and the inductance of the narrow conducting segments 1156 resemble a filter that allows current in the low frequency band to pass while attenuating current in the higher cellular frequency band. Parasitic element 1152A shown in fig. 13A is designed to mask over the full mid-band cellular frequency band (1.4-2.7 GHz). Parasitic element 1152B shown in fig. 13B is designed to mask over the original mid-band cellular band (1.69-2.7 GHz). Parasitic element 1152C shown in fig. 13C is designed to mask over a portion of the high-band cellular band (i.e., 3.1-4.2 GHz).

One problem with the conventional parasitic elements of fig. 13A-13C is that they tend to function more like a band reject filter rather than a low pass filter. Thus, the conventional parasitic elements 1152A, 1152B, 1152C of fig. 13A-13C generally provide good performance only on the mid-band or high-band, or in many cases, only for a portion of the mid-band or high-band cellular band. Thus, a base station antenna manufacturer may need to manufacture and store a variety of different parasitic elements designed to be masked in different frequency ranges and select the appropriate parasitic element for use in each base station antenna design depending on the type of array included therein. Furthermore, in recent years, the high-band frequency range has been extended such that some base station antennas now include arrays operating in the 3.1-5.8GHz frequency band. In general, the conventional parasitic element designs shown in fig. 13A-13C do not mask well over such a wide frequency range. As discussed above, if a plurality of low-band parasitic elements mounted adjacent to a low-band array are not masked within the operating frequency range of an adjacent mid-band or high-band array, it may be difficult to find the mounting locations of the parasitic elements that improve the performance of the low-band array without degrading the performance of the adjacent mid-band or high-band array. This same problem may occur when the parasitic element is masked only on a portion of the operating frequency band of the adjacent mid-band or high-band array. Thus, the conventional parasitic element designs shown in fig. 13A-13C may not be suitable for use with low band arrays located near high band arrays operating in all or most of the 3.1-5.8GHz frequency range.

According to a further embodiment of the invention, a parasitic element for a base station antenna is provided, which parasitic element is designed to resonate with respect to RF energy emitted by a low-band radiating element while being substantially transparent to RF energy emitted by a mid-band and/or high-band radiating element. In an exemplary embodiment, these parasitic elements may resonate in some or all of the low-band frequency range (617-960 MHz) while exhibiting good masking behavior over the full 1.4-5.8GHz band. Accordingly, the masking parasitic element according to the embodiment of the present invention can be used in the entire range of the base station antenna, and can exhibit improved performance compared to conventional masking parasitic elements.

The masked parasitic element according to embodiments of the present invention may include a first stacked serpentine conductive path and a second stacked serpentine conductive path, and may be, for example, substantially identical to the masked dipole arms described above. In other words, the parasitic element according to the embodiment of the present invention may have the same design as the dipole arm of the above-described radiation element according to the embodiment of the present invention.

Fig. 14A-14C illustrate an exemplary embodiment of a masking parasitic element 1252 in accordance with an embodiment of the invention. In particular, fig. 14A is a plan view of the masking parasitic element 1252, fig. 14B is a perspective view of two metal patterns of the parasitic element 1252, and fig. 14C is a schematic side view of a portion of the parasitic element 1252.

As shown in fig. 14A-14C, the parasitic element 1252 may be implemented on a printed circuit board 1260 that includes a dielectric substrate 1262 and first and second conductive patterns 1264 and 1266 formed on opposite sides thereof. The conductive patterns 1264, 1266 may include patterned copper, and a protective dielectric coating (not shown) may cover and protect the conductive patterns 1264, 1266. The first conductive pattern 1264 may define a first plane and the second conductive pattern 1266 may define a second plane parallel to and spaced apart from the first plane.

As best shown in fig. 14B, the first conductive pattern 1264 forms a first conductive path 1270 and the second conductive pattern 1266 forms a second conductive path 1280 parallel to and spaced apart from the first conductive path 1270. The first conductive path 1270 and the second conductive path 1280 may be serpentine conductive paths. Each conductive path 1270, 1280 may include a thin conductive trace having a length that is much longer than its width. In the depicted embodiment, the first conductive path 1270 and the second conductive path 1280 each have the shape of a square wave. The first serpentine conductive path 1270 includes a plurality of first longitudinal segments 1272 that extend generally parallel to the longitudinal axis 1254 of the parasitic element 1252 and a plurality of first lateral segments 1274 that extend generally perpendicular to the longitudinal axis 1254 of the parasitic element 1252. Likewise, the second serpentine conductive path 1280 includes a plurality of second longitudinal segments 1282 extending generally parallel to the longitudinal axis 1254 of the parasitic element 1252 and a plurality of second transverse segments 1284 extending generally perpendicular to the longitudinal axis 1254 of the parasitic element 1252. For each conductive path 1270, 1280, the longitudinal segments 1272, 1282 and the transverse segments 1274, 1284 alternate to form a square wave.

At least some of the first lateral segments 1274 overlap respective ones of the second lateral segments 1284 to form a plurality of pairs 1290 of overlapping first lateral segments 1274 and second lateral segments 1284. As described above, a first segment and a second segment of the conductive path "overlap" if an axis perpendicular to the plane defined by the first segment passes through both the first segment and the second segment. In the depicted embodiment, the second serpentine conductive path 1280 defines a square wave having a frequency that is twice the frequency of the square wave defined by the first serpentine conductive path 1270. Thus, each first lateral segment 1274 of the first serpentine conductive path 1270 overlaps a corresponding second lateral segment 1284 of the second serpentine conductive path 1280, but only half of the second lateral segments 1284 have corresponding overlapping first lateral conductive segments 1274.

As with the similar dipole arms discussed above, each pair 1290 of overlapping first and second transverse segments 1274, 1284 is designed to inhibit the formation of current on the first and second serpentine conductive paths 1270, 1280 in response to RF radiation emitted by nearby mid-band or high-band radiating elements. In particular, each pair 1290 of overlapping first and second lateral segments 1274, 1284 may be configured such that the instantaneous direction of a first current formed on a first lateral segment 1274 of the pair 1290 in response to RF radiation emitted by a nearby mid-band or high-band radiating element will be substantially opposite to the instantaneous direction of a second current formed on a second lateral segment 1284 of the pair 1290 in response to mid-band or high-band RF radiation, and these opposite currents cancel each other.

The width of the metal traces forming the serpentine conductive paths 1270, 1280 may be selected such that low-band currents may flow relatively freely on the serpentine conductive paths 1270, 1280 while mid-band and/or high-band currents are substantially suppressed. In some embodiments, the width of each serpentine conductive path 1270, 1280 may be selected to be, for example, less than 0.05, which corresponds to the wavelength of the lowest frequency RF signal to be suppressed. The use of conductive traces having narrow widths creates an inductive effect that appears as a high impedance to higher frequency RF signals, thereby suppressing the formation of current from such radiation, while having a sufficiently low impedance to lower frequency RF signals (allowing current generated by such lower frequency RF signals to flow on conductive paths 1270, 1280). The serpentine conductive paths 1270, 1280 form an LC resonant circuit. By selecting the appropriate width for the traces forming the serpentine conductive paths 1270, 1280, the LC circuit may appear as an open circuit at its resonant frequency, which may be at mid-band/high-band frequencies. Accordingly, the parasitic element 1252 is designed to allow a low-band current to flow thereon while suppressing the formation of a middle-band current and a high-band current. This suppression tends to increase with increasing frequency, providing broadband performance.

Additionally, the "length" of each lateral segment 1274, 1284, or alternatively, the average length of all lateral segments on a given conductive path may be selected to be less than one-fourth of the wavelength corresponding to the lowest frequency RF signal to be suppressed. Thus, for example, in an exemplary embodiment, the length of each lateral segment 1274, 1284 (or the average length of the lateral segments 1274, 1284 on each conductive path 1270, 1280) may be selected to be less than one-fourth of the wavelength corresponding to 1427MHz frequency or 1690MHz frequency (e.g., the exemplary lowest frequency of the operating band of the mid-band radiating element). In other embodiments, the average length of the transverse segments 1274 on the first serpentine conductive path 1270 and the average length of the transverse segments 1284 on the second serpentine conductive path 1280 may each be less than 1/4 of a wavelength corresponding to the center frequency of the operating band of the mid-band radiating element.

Fig. 15 is a graph comparing the magnitude of the current induced on the conventional parasitic element 1152A of fig. 13A with the magnitude of the current induced on the parasitic element 1252 according to the embodiment of the invention of fig. 14A-14C. It can be seen that the two parasitic elements 1152A, 1252 resonate within the low-band frequency range, so that low-band current will flow on the two parasitic elements 1152A, 1252 and RF energy radiated in response to these currents will be emitted in a direction that helps to reduce the azimuth beamwidth of the antenna beam generated by the low-band radiating elements. The two parasitic elements 1152A, 1252 also substantially suppress current flow in the conventional mid-band frequency range (1695-2690 MHz). However, it can be seen that the minimum rejection in this band is significantly higher for parasitic element 1252, because the peak in the response of parasitic element 1250 at 1600MHz is about 8dB lower than the peak in the response of parasitic element 1152A at 1600MHz, in accordance with an embodiment of the present invention.

It can also be seen from fig. 15 that at higher frequencies, current begins to flow easily over the conventional parasitic element 1152A. The current rises to a substantially unacceptable level at about 3GHz and steadily climbs therefrom such that at frequencies above 4GHz the magnitude of the current is within about 1dB of the peak magnitude of the current in the low band frequency range. In contrast, parasitic element 1252 in accordance with embodiments of the invention continues to exhibit strong masking performance throughout the 1695-5800MHz frequency range.

The parasitic elements 1252 may be mounted in the manner shown in fig. 11, i.e., an array of parasitic elements 1252 may extend in a longitudinal direction on opposite sides of the low-band array of radiating elements, wherein the parasitic elements 1252 are positioned in front of the reflector of the antenna, wherein a longitudinal axis 1254 of each parasitic element 1252 extends parallel to the longitudinal axis of the antenna, and wherein a plane defined by the first major surface of each parasitic element 1252 extends perpendicular to the reflector. This is illustrated in fig. 16A-16B, which are schematic front views of base station antennas 1300A, 1300B, respectively, that include parasitic elements 1352 (e.g., parasitic elements 1352 may be implemented using parasitic element 1252 of fig. 14A-14C) in accordance with embodiments of the invention.

Referring first to fig. 16A, a base station antenna 1300A includes a low-band linear array 1320 including a column of low-band radiating elements 1324 and a pair of mid-band arrays 1330-1, 1330-2 each including a column of mid-band radiating elements 1334. All radiating elements 1324, 1334 are mounted to extend forward from reflector 1310. The mid-band array 1330 is positioned on the opposite side of the low-band linear array 1320. The first array 1350-1 of parasitic elements extends longitudinally such that the first mid-band array 1330-1 is between the first array 1350-1 of parasitic elements 1352 and the low-band array 1320 and the second array 1350-2 of parasitic elements 1352 extends longitudinally such that the second mid-band array 1330-2 is between the second array 1350-2 of parasitic elements 1352 and the low-band array 1320.

Referring next to fig. 16B, the base station antenna 1300B includes first and second low-band linear arrays 1320-1 and 1320-2 of low-band radiating elements 1324, first and second mid-band linear arrays 1330-1 and 1330-2 of mid-band radiating elements, and a multi-column high-band array 1340 of high-band radiating elements 1344. Radiating elements 1324, 1334, 1344 are mounted to extend forward from reflector 1310. The first array 1350-1 of parasitic elements 1352 extends longitudinally such that the first mid-band array 1330-1 is between the first array 1350-1 of parasitic elements 1352 and the first low-band array 1320-1 and the second array 1350-2 of parasitic elements 1352 extends longitudinally such that the second mid-band array 1330-2 is between the second array 1350-2 of parasitic elements 1352 and the second low-band array 1320-2. The high band array 1340 is positioned between the two low band arrays 1320-1, 1320-2.

While the parasitic elements 1352 shown in fig. 16A-16B are mounted such that the plane defined by the first major surface of each parasitic element 1352 extends perpendicular to the reflector 1310 (i.e., they are mounted as shown in fig. 11), it should be understood that embodiments of the present invention are not so limited. For example, in other embodiments, each parasitic element 1352 may be rotated 90 ° about its longitudinal axis such that the first major surface of each parasitic element 1352 extends parallel to reflector 1310, or may be rotated an angle other than 90 °.

It should also be appreciated that parasitic elements according to embodiments of the present invention may be mounted in other orientations. For example, fig. 17 illustrates how the conventional parasitic element 1052 shown in fig. 12 may be replaced with a parasitic element 1452 in accordance with embodiments of the present invention. Each parasitic element 1452 is mounted to extend forward from reflector 1410, and parasitic element 1452 may be mounted to form a box around radiating element 1444.

Referring again to fig. 15, in some cases, parasitic elements in accordance with embodiments of the present invention may exhibit reduced passband performance as compared to conventional parasitic elements. For example, as can be seen in fig. 15, the peak current in the passband of the conventional parasitic element 1152A of fig. 13A is approximately 1.4dB higher than the peak current in the passband of the parasitic element 1252 of fig. 14A-14C, and the peak current in the passband of the parasitic element 1252 of fig. 14A-14C drops faster than the peak current in the passband of the conventional parasitic element 1152A.

According to a further embodiment of the present invention, a base station antenna is provided, comprising an array of radiating elements having an associated array of parasitic elements comprising at least two different parasitic element designs. As discussed above with reference to, for example, fig. 15, each parasitic element may resonate at a frequency within the operating frequency band of the associated linear array. This resonant frequency will correspond to the frequency at which the highest current flow will occur on the parasitic element. For some parasitic element designs, the current level may begin to drop slightly rapidly as the frequency of the RF energy moves away from the resonant frequency, as shown in fig. 15. When this occurs, the parasitic elements may not shape the antenna beam across the entire operating band of the associated radiating element array in a desired manner.

If higher passband performance is desired, each parasitic element 1352 in the base station antenna 1300A, 1300B of fig. 16A and 16B, for example, may be replaced with a pair of stacked parasitic elements 1552-1, 1552-2 (e.g., stacked in the forward direction of the base station antenna), where each parasitic element 1552 is designed to have peak resonance at a different frequency within the low frequency band (e.g., one parasitic element may have peak current flow at 725MHz and the other at 840 MHz). This may improve the ability of the parasitic element to shape the low-band antenna beam across the entire low-band frequency range, and should not reduce the masking ability of the parasitic element. Fig. 18 illustrates an exemplary embodiment of a "dual" parasitic element that includes a first parasitic element 1552-1 and a second parasitic element 1552-2 having different resonant frequencies. As shown in fig. 18, in some embodiments, the two parasitic elements 1552-1, 1552-2 may be implemented as part of a single printed circuit board. It will also be appreciated that three or more parasitic elements may be used, each having a different resonant frequency to further improve the performance of the associated radiating element array.

As is apparent from the above description, according to further embodiments of the present invention, there is provided a base station antenna comprising a reflector and first and second arrays of radiating elements extending forwardly from the reflector. The radiating elements of the first array operate in a lower operating frequency band (e.g., 617-960MHz band or a portion thereof) and the radiating elements of the second array operate in a higher operating frequency band (e.g., 1427-2690MHz band or a portion thereof, or 3.1-5.8GHz band or a portion thereof). These antennas also include one or more parasitic elements. For example, the antenna may include a first vertically extending column of parasitic elements positioned on a first side of the first array and a second vertically extending column of parasitic elements positioned on a second, opposite side of the first array. At least some of the parasitic elements include a first conductive path and a second conductive path, wherein the second conductive path is positioned rearward of the first conductive path. The first conductive path includes a plurality of first segments and the second conductive path includes a plurality of second segments. The subset of first segments overlaps respective ones of the second segments in the subset of second segments to form a plurality of pairs of overlapping first and second segments. At least some of each pair of overlapping first and second segments are configured such that the instantaneous direction of a first current formed on the first segment in response to RF radiation emitted by the radiating elements in the second array will be substantially opposite to the instantaneous direction of a second current formed on the second segment in response to RF radiation emitted by the radiating elements of the second array. As a result, currents induced on the first segment and the second segment may substantially cancel, such that the parasitic element may be substantially transparent to RF radiation in the second operating frequency band. The parasitic element may resonate at a frequency within the first operating band such that the parasitic element will change a characteristic of an antenna beam generated by a first one of the desired arrays. For example, the parasitic element may reduce the azimuth beamwidth of the antenna beam generated by the first array or may improve the cross-polarization discrimination performance of the radiating elements in the first array.

In some embodiments, the first and second conductive paths of the parasitic element described above may have a wave structure (e.g., square wave, sine wave, etc.). The wave structure of the first conductive path may have a first frequency and the wave structure of the second conductive path may have a second frequency different from the first frequency. In some embodiments, the first frequency and the second frequency may differ substantially by a multiple of an integer (e.g., two times, three times, etc.).

In some embodiments, the first conductive path and the second conductive path may each be a serpentine conductive path. The first serpentine conductive path can include a plurality of first longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of first transverse segments extending generally perpendicular to the first longitudinal segments, and the second serpentine conductive path can include a plurality of second longitudinal segments extending generally parallel to the longitudinal axis of the antenna and a plurality of second transverse segments extending generally perpendicular to the second longitudinal segments. In some embodiments, substantially all of the first lateral segments may overlap with respective ones of the second lateral segments. In some embodiments, in at least some of the pairs of overlapping first and second segments, one of the first and second segments may fully overlap the other of the first and second segments.

Discussion of parasitic elements according to embodiments of the present invention has focused on parasitic elements having designs corresponding to the dipole arms of the radiating elements described above with reference to fig. 4A-4F and 5A-5B. However, it should be appreciated that parasitic elements according to embodiments of the present invention may have any of the designs of the masked dipole arms described herein, including in particular designs such as those discussed above with reference to fig. 6-9. Thus, it should be appreciated that masking parasitic elements in accordance with embodiments of the present invention may have a variety of different implementations.

When such "double" (or triple) parasitic elements are used, one of the "double" parasitic elements 1552-1, 1552-2 shown in fig. 18 may be used, for example, to replace each of the parasitic elements 952 shown in antenna 900 of fig. 11. In an exemplary embodiment, the resonant frequency of the first parasitic element may differ from the resonant frequency of the second parasitic element by, for example, at least 5% or at least 10%.

It will be appreciated that many modifications may be made to the radiating element and antenna described above without departing from the scope of the present invention. For example, the low-band radiating element described above includes a dipole radiator printed circuit board, and each of four dipole arms is implemented in the dipole radiator printed circuit board. However, it should be appreciated that in other embodiments, more than one dipole radiator printed circuit board may be used. For example, each dipole arm may be implemented on its own dipole radiator printed circuit board.

While the exemplary embodiments described above have low band radiating elements designed to be transparent to RF energy radiated in two higher bands, it should be appreciated that embodiments of the present invention are not so limited. For example, in other embodiments, a mid-band radiating element may be provided having a first dipole arm configured to be substantially transparent to RF energy in a lower band and a second dipole arm configured to be substantially transparent to RF energy in a higher band.

Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, 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. Like numbers refer to like elements throughout.

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 element. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

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

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

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

Aspects and elements of all 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. An antenna, comprising:

A reflector;

A first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band; and

A second radiating element extending forward from the reflector, the second radiating element configured to operate in a second operating frequency band that includes a higher frequency than the first operating frequency band;

Wherein the first radiating element comprises a first dipole radiator having a first dipole arm and a second dipole arm, and a second dipole radiator having a third dipole arm and a fourth dipole arm,

Wherein the first dipole arm comprises a first conductive path and a second conductive path positioned behind the first conductive path,

Wherein the first conductive path comprises a plurality of first segments and the second conductive path comprises a plurality of second segments, wherein a subset of the first segments overlap respective ones of the second segments in the subset of second segments to form a plurality of pairs of overlapping first and second segments,

Wherein at least some of each pair of overlapping first and second segments are configured such that a transient direction of a first current formed on the first segment in response to radio frequency ("RF") radiation emitted by the second radiating element will be substantially opposite to a transient direction of a second current formed on the second segment in response to RF radiation emitted by the second radiating element.

2. The antenna of claim 1, wherein the first conductive path comprises a first serpentine conductive path and the second conductive path comprises a second serpentine conductive path.

3. The antenna of claim 1 or 2, wherein the first conductive path is implemented in a first metal layer of a printed circuit board and the second conductive path is implemented in a second metal layer of the printed circuit board.

4. The antenna of claim 2 or 3, wherein the first serpentine conductive path comprises a plurality of first longitudinal segments extending substantially parallel to a longitudinal direction of the first dipole arm and a plurality of first transverse segments extending substantially perpendicular to the longitudinal direction of the first dipole arm.

5. The antenna of claim 4, wherein the second serpentine conductive path comprises a plurality of second longitudinal segments extending substantially parallel to a longitudinal direction of the first dipole arm and a plurality of second transverse segments extending substantially perpendicular to a longitudinal direction of the first dipole arm.

6. The antenna defined in claim 5 wherein at least some of the pairs of overlapping first and second segments comprise respective ones of the first and second transverse segments.

7. The antenna defined in claim 5 wherein substantially all of the first lateral segments overlap with respective ones of the second lateral segments.

8. The antenna defined in any one of claims 1-7 wherein in at least some of the pairs of overlapping first and second segments one of the first and second segments fully overlaps the other of the first and second segments.

9. The antenna of any of claims 1-8, wherein at least one of the first transverse segments is wider than at least one of the first longitudinal segments.

10. The antenna defined in any one of claims 1-9 wherein the first radiating element further comprises a feed handle having a feed line and wherein the first conductive path is galvanically connected to the feed line and the second conductive path is galvanically coupled to the feed handle.

11. The antenna of any of claims 1-10, wherein the first and second conductive paths of each of the first through fourth dipole arms form respective closed loops.

12. The antenna of any of claims 2-11, wherein the first serpentine conductive path comprises a wave structure having a first frequency and the second serpentine conductive path comprises a wave structure having a second frequency different from the first frequency.

13. The antenna of any of claims 1-12, wherein the second dipole arm includes a third conductive path that is substantially identical to the first conductive path and a fourth conductive path that is substantially identical to the second conductive path, and wherein the first dipole arm overlaps the second radiating element.

14. The antenna of any of claims 1-13, further comprising a third radiating element extending forward from the reflector, the third radiating element configured to operate in a third operating frequency band that includes a higher frequency than the second operating frequency band, wherein the second dipole arm overlaps the third radiating element.

15. The antenna of claim 14, wherein the first dipole arm and the second dipole arm are configured to be substantially transparent to RF signals in the second operating frequency band and in the third operating frequency band.

16. The antenna defined in any one of claims 1-15 wherein the first radiating element further comprises at least one feed stalk that extends generally perpendicular to the reflector and wherein each of the first to fourth dipole arms comprises first and second spaced apart conductive segments that together form a generally oval shape.

17. The antenna of claim 4, wherein an average length of the first lateral segment is less than 1/4 of a wavelength corresponding to a center frequency of the second operating band.

18. The antenna of claim 5, wherein an average width of the first serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band and an average width of the second serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band.

19. A radiating element, comprising:

A first dipole radiator having a first dipole arm and a second dipole arm, and a second dipole radiator having a third dipole arm and a fourth dipole arm,

Wherein the first dipole arm includes a first serpentine conductive path extending from a base of the first dipole arm to a distal end of the first dipole arm and a second serpentine conductive path positioned rearward of the first serpentine conductive path.

20. The antenna of claim 19, wherein an average width of the first serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band and an average width of the second serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band.

21. The radiating element of claim 19 or 20, wherein the first serpentine conductive path comprises a plurality of first longitudinal segments extending generally parallel to a longitudinal direction of the first dipole arm and a plurality of first transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm, and wherein the second serpentine conductive path comprises a plurality of second longitudinal segments extending generally parallel to the longitudinal direction of the first dipole arm and a plurality of second transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm.

22. The antenna of claim 21, wherein an average length of the first lateral segment is less than 1/4 of a wavelength corresponding to a center frequency of the second operating band.

23. The radiating element of claim 21 or 22, wherein at least some of the first transverse segments overlap with respective ones of the second transverse segments.

24. The radiating element of claim 21 or 22, wherein substantially all of the first transverse segments overlap with respective ones of the second transverse segments.

25. The radiating element of any of claims 21-24, wherein at least some of the first transverse segments completely overlap with respective ones of the second transverse segments.

26. The radiating element of any of claims 21-25, wherein at least one of the first transverse segments is wider than at least one of the first longitudinal segments.

27. The radiating element of any of claims 21-26, wherein the first radiating element further comprises a feed handle having a feed line, and wherein the first serpentine conductive path is galvanically connected to the feed line and the second serpentine conductive path is galvanically coupled to the feed handle.

28. The radiating element of any of claims 19-27, wherein the first serpentine conductive path and the second serpentine conductive path form respective closed loops.

29. The radiating element of any of claims 19-28, wherein the first serpentine conductive path comprises a wave structure having a first frequency and the second serpentine conductive path comprises a wave structure having a second frequency different from the first frequency.

30. The radiating element of any of claims 19-29, wherein the first serpentine conductive path has a generally oval shape.

31. The radiating element of claim 30, wherein the second serpentine conductive path has a substantially oval shape.

32. The radiating element of any of claims 19-31, wherein the first serpentine conductive path comprises a plurality of first wave segments each having a wave structure, and a plurality of first transition segments connecting respective adjacent pairs of first wave segments.

33. The radiating element of claim 32, wherein the second serpentine conductive path comprises a plurality of second wave segments each having a wave structure, and a plurality of second transition segments connecting respective adjacent pairs of second wave segments.

34. An antenna, comprising:

A reflector;

a first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band, the first radiating element comprising a first dipole arm; and

A second radiating element extending forwardly from the reflector, the second radiating element configured to operate in a second operating frequency band comprising a higher frequency than the first operating frequency band,

Wherein the first dipole arm includes a first conductive path and a second conductive path spaced apart from each other,

Wherein a first segment of the first conductive path overlaps a second segment of the second conductive path,

Wherein the first dipole arms are configured such that first and second currents induced on respective first and second conductive paths in response to radio frequency ("RF") radiation emitted by the second radiating element each flow outwardly along the first dipole arms but in substantially opposite directions along respective first and second segments.

35. The antenna defined in claim 34 wherein the first radiating element comprises a first dipole radiator and a second dipole radiator, the first dipole radiator comprising the first and second dipole arms, the second dipole radiator having a third and fourth dipole arm, and wherein each dipole arm comprises a base adjacent a center of the first radiating element and a distal end positioned outside the base.

36. The antenna of claim 34 or 35, wherein the first conductive path comprises a first serpentine conductive path and the second conductive path comprises a second serpentine conductive path.

37. The antenna of any of claims 34-36, wherein the first conductive path is implemented in a first metal layer of a printed circuit board and the second conductive path is implemented in a second metal layer of the printed circuit board.

38. The antenna of claim 36, wherein the first serpentine conductive path comprises a plurality of first longitudinal segments extending generally parallel to a longitudinal direction of the first dipole arm and a plurality of first transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm, and the second serpentine conductive path comprises a plurality of second longitudinal segments extending generally parallel to the longitudinal direction of the first dipole arm and a plurality of second transverse segments extending generally perpendicular to the longitudinal direction of the first dipole arm.

39. The antenna defined in claim 38 wherein the first section comprises one of the first lateral sections and the second section comprises one of the second lateral sections.

40. The antenna of claim 38, wherein an average length of the first lateral segment is less than 1/4 of a wavelength corresponding to a center frequency of the second operating band.

41. The antenna of claim 38, wherein an average width of the first serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band and an average width of the second serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band.

42. The antenna of claim 38, wherein the first serpentine conductive path comprises a wave structure having a first frequency and the second serpentine conductive path comprises a wave structure having a second frequency different than the first frequency.

43. An antenna, comprising:

A reflector;

A first radiating element extending forward from the reflector, the first radiating element configured to operate in a first operating frequency band;

A second radiating element extending forward from the reflector, the second radiating element configured to operate in a second operating frequency band that includes a higher frequency than the first operating frequency band; and

A parasitic element including a first conductive path and a second conductive path positioned behind the first conductive path,

44. The antenna of claim 43, wherein the first conductive path comprises a first serpentine conductive path and the second conductive path comprises a second serpentine conductive path.

45. The antenna of claim 43 or 44, wherein the first conductive path is implemented in a first metal layer of a printed circuit board and the second conductive path is implemented in a second metal layer of the printed circuit board.

46. The antenna of claim 44 or 45, wherein the first serpentine conductive path comprises a plurality of first longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of first transverse segments extending generally perpendicular to the first longitudinal segments.

47. The antenna of claim 46, wherein the second serpentine conductive path comprises a plurality of second longitudinal segments extending substantially parallel to a longitudinal axis of the antenna and a plurality of second transverse segments extending substantially perpendicular to the second longitudinal segments.

48. The antenna of claim 47, wherein at least some of the pairs of overlapping first and second segments comprise respective ones of the first and second lateral segments.

49. The antenna of claim 47, wherein substantially all of the first lateral segments overlap with respective ones of the second lateral segments.

50. The antenna of any of claims 43-49, wherein in at least some of the pairs of overlapping first and second segments, one of the first and second segments completely overlaps the other of the first and second segments.

51. The antenna of any of claims 44-50, wherein the first serpentine conductive path comprises a wave structure having a first frequency and the second serpentine conductive path comprises a wave structure having a second frequency different from the first frequency.

52. The antenna of any of claims 43-51, further comprising a third radiating element extending forward from the reflector, the third radiating element configured to operate in a third operating frequency band containing higher frequencies than the second operating frequency band, wherein the parasitic element is configured to be substantially transparent to RF signals in the second operating frequency band and in the third operating frequency band.

53. The antenna of any of claims 44-52, wherein an average width of the first serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band and an average width of the second serpentine conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band.

54. The radiating element of any of claims 43-54, wherein the parasitic element comprises a first parasitic element, the antenna further comprising a second parasitic element comprising a first conductive path and a second conductive path positioned behind the first conductive path, wherein the first parasitic element and the second parasitic element are positioned adjacent to the first radiating element, and wherein a resonant frequency of the first parasitic element is different from a resonant frequency of the second parasitic element.

55. The radiating element of claim 54, wherein the resonant frequency of the first parasitic element differs from the resonant frequency of the second parasitic element by at least 5%.

56. The radiating element of claim 54 or 55, wherein the first parasitic element and the second parasitic element are implemented in a common printed circuit board.

57. An antenna, comprising:

a first radiating element configured to operate in a first operating frequency band;

A second radiating element configured to operate in a second operating frequency band that does not overlap the first operating frequency band and that includes a higher frequency than the first operating frequency band; and

A parasitic element positioned adjacent to the first radiating element and the second radiating element, the parasitic element comprising a first conductive path having a wave structure with a first frequency and a second conductive path positioned behind the first conductive path having a wave structure with a second frequency, wherein the first frequency is different than the second frequency.

58. The antenna of claim 57, wherein an average width of the first conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band and an average width of the second conductive path is less than 0.05 of a wavelength corresponding to a center frequency of the second operating band.

59. The radiating element of claim 57 or 58, wherein the first conductive path comprises a plurality of first longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of first transverse segments extending generally perpendicular to the first longitudinal segments, and the second conductive path comprises a plurality of second longitudinal segments extending generally parallel to a longitudinal axis of the antenna and a plurality of second transverse segments extending generally perpendicular to the second longitudinal segments.

60. The radiating element of claim 59, wherein at least some of the first transverse segments overlap respective ones of the second transverse segments.

61. The radiating element of claim 60, wherein substantially all of the first transverse segments overlap respective ones of the second transverse segments.

62. The radiating element of claim 59, wherein at least some of the first transverse segments completely overlap respective ones of the second transverse segments.

63. The radiating element of claim 57, wherein the parasitic element comprises a first parasitic element, the antenna further comprising a second parasitic element comprising a first conductive path and a second conductive path positioned rearward of the first conductive path, wherein the first parasitic element and the second parasitic element are positioned adjacent the first radiating element, and wherein a resonant frequency of the first parasitic element is different than a resonant frequency of the second parasitic element.

64. The radiating element of claim 63, wherein the resonant frequency of the first parasitic element differs from the resonant frequency of the second parasitic element by at least 5%.

65. The radiating element of claim 64, wherein the first parasitic element and the second parasitic element are implemented in a common printed circuit board.