Dual polarized radiating elements for base station antennas with built-in common mode rejection filter for blocking common mode radiation

Abstract

The present disclosure relates to dual-polarized radiating elements for base station antennas with built-in handle filters that block common mode radiation parasitics. The antennas include radiators electrically coupled to feed handles having a common mode rejection (CMR) filter therein. The CMR filter is configured to suppress common mode radiation from the radiators by providing a frequency-dependent impedance to a pair of common mode currents within the feed handle sufficient to increase return loss associated with the pair of common mode currents to a level greater than -6 dB over a frequency range that includes a frequency of the common mode radiation.

Description

[0001] REFERENCE TO PRIOR APPLICATION

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 140,742, filed January 22, 2021, and U.S. Patent Application No. 17 / 552,390, filed December 16, 2021. TECHNICAL FIELD

[0003] The present invention relates to radio communication and antenna apparatus, and more particularly to dual-polarized antennas for cellular communication and methods of operating dual-polarized antennas. BACKGROUND

[0004] Cellular communication systems are well known in the art. In a typical cellular communication system, a geographic region is generally divided into a series of areas, commonly referred to as “cells,” which are served by corresponding base stations. Each base station can include one or more base station antennas (BSAs) configured to provide bidirectional radio frequency (“RF”) communication with mobile users within the cell served by the base station. In many cases, each base station is divided into “sectors.” In perhaps the most common configuration, a hexagonal-shaped cell is divided into three 120° sectors, and each sector is served by one or more base station antennas that can have an approximately 65° azimuthal half-power beamwidth (HPBW), providing sufficient coverage for each 120° sector. Typically, the base station antennas are mounted on a tower or other elevated structure, with the radiation pattern (also referred to as the “antenna beam”) pointing outward therefrom. The base station antennas are typically implemented as linear or planar phased arrays of radiating elements.

[0005] Moreover, to accommodate growing cellular traffic, cellular operators have added cellular service in various frequency bands. While in some cases, a single linear array of so-called “wideband” radiating elements can be used to provide service in multiple frequency bands, in other cases, different linear arrays of radiating elements can have to be used in a multi-band base station antenna to support service in the additional frequency bands.

[0006] One conventional multi-band base station antenna design includes at least one linear array of relatively “low-band” radiating elements that can be used to provide service in some or all of the 617-960 MHz frequency band, and at least two linear arrays of relatively “high-band” radiating elements that are used to provide service in some or all of the 1695-2690 MHz frequency band.

[0007] Conventional box-shaped dipole radiating elements can include four dipole radiators arranged to define a box-like shape. The four dipole radiators can extend in a common plane and can be mounted forward of a reflector that can extend parallel to the common plane. So-called feed stalks can be used to mount the four dipole radiators forward from the reflector and can be used to pass RF signals between the dipole radiators and other components of the antenna. In some of these conventional box-shaped dipole radiating elements, a total of eight feed stalks (4 x 2) can be provided and can be connected to the box-shaped dipole radiators at the corners of the box.

[0008] For example, as shown by FIGS. 1A-1B, a conventional multi-band radiator 10 for a base station antenna can include a relatively high-band radiating element 10a centered within and surrounded on four sides by a relatively low-band radiating element 10b configured as a box-shaped dipole radiating element ("box dipole"). RF signals can be fed to the four dipole radiators of the conventional box dipole radiating element through feed stalks at two opposite and "energized" corners of the "box," as shown in FIG. 1A. In response to the differential mode (DM) currents fed to the two energized "differential mode" ports, a common mode (CM) current is automatically imposed onto the two diametrically opposite and un-energized corners of the box. And, since these common mode currents radiate as monopoles on these "un-energized" feed stalks, the overall radiation pattern of the box dipole 10b is effectively a combination of two dipoles and two monopoles (with "nulls"), as shown by the simplified radiation pattern of FIG. 1B. Unfortunately, the radiation resulting from the monopole operation can be highly undesirable when designing a box dipole radiator. For example, while the common mode currents radiate at the same time as the differential mode currents in the box dipole 10b, the azimuthal HPBW of the box dipole 10b can be expected to be slightly reduced because of the two nulls caused by the monopole radiators, the concurrent co-polarized radiation pattern of the box dipole 10b can be expected to exhibit elevated "shoulders" in the radiation pattern, which can significantly degrade overall antenna performance.

[0009] Referring now to FIGS. 2A-2B, a conventional cross-polarized box dipole radiating element 20, 20' (with inwardly tilted feed stalks and thus tilted monopoles) is shown that operates in a similar manner with respect to the low-band radiating element 10b of FIG. 1A. Thus, as shown, energization of a first pair of diametrically opposite "differential mode" ports of the box dipole radiating element 20, 20' can induce common mode (CM) currents in a corresponding second pair of ports, which results in monopole-type radiation from a pair of tilted monopoles. And, as also shown by FIG. 2A, this monopole-type radiation can result in the creation of an undesirable "shoulder" (S) in the azimuthal radiation pattern associated with the box dipole 20. SUMMARY

[0010] Dual-polarized radiating elements for base station antennas (BSAs) can utilize stalk-based filters to suppress common-mode radiative parasitics. According to some embodiments of the present invention, an antenna radiating element is provided with a first radiator arm and a second radiator arm that can be supported in front of a substrate by a feed stalk. The feed stalk includes a first feed path electrically coupled to the first radiator arm, a second feed path electrically coupled to the second radiator arm, and a common-mode rejection filter having a first port and a second port electrically connected to the first feed path and the second feed path, respectively. The common-mode rejection filter includes a pair of coupled inductors therein. In some embodiments of the present invention, the pair of coupled inductors can be disposed intermediate a base and a distal end of the feed stalk.

[0011] The pair of coupled inductors includes (i) a first inductor having a current carrying terminal electrically coupled to the first port of the common-mode rejection filter, and (ii) a second inductor having a current carrying terminal electrically coupled to the second port of the common-mode rejection filter. The feed stalk can also be configured as a printed circuit board having patterned metallization on first and second opposing faces thereof, and the pair of coupled inductors can be defined by the patterned metallization on the first and second opposing faces of the printed circuit board. Additionally, the first feed path can be electrically connected to the first inductor of the pair of coupled inductors, and the second feed path can be electrically connected to the second inductor of the pair of coupled inductors by a plated through hole in the printed circuit board.

[0012] According to additional embodiments of the present invention, the common-mode rejection filter is configured such that a first impedance electrically coupled to the first port is equal to Z1, and a second impedance electrically coupled to the second port is equal to Z2, where: Z1 = R1 + jωL1 + jωM(I2 / I1); Z2 = R2 + jωL2 + jωM(I1 / I2); R1 and R2 are the resistances of the first and second inductors, respectively; L1 and L2 are the inductances of the first and second inductors, respectively; M is the mutual inductance between the first and second inductors; I1 and I2 are the first and second currents flowing into the first and second ports, respectively; and ω is the angular frequency of the first and second currents. These impedances Z1 and Z2 are configured to block common-mode signals having a high frequency-dependent reactance when I1 is equal to I2, but to selectively and effectively pass differential-mode signals having a very low resistance when I1 is equal to -I2.

[0013] In other embodiments of the invention, the antenna is configured as a box dipole antenna having first through fourth feed ports in communication with respective first through fourth corners of the box dipole. The first feed port is disposed at the first corner and is electrically coupled to the first and second feed paths by the common mode rejection filter. In other embodiments of the invention, the antenna is configured as a loop antenna having at least a first feed port that is electrically coupled to the first and second feed paths by a common mode rejection filter.

[0014] According to additional embodiments of the invention, a box dipole antenna is provided that includes a first dipole radiator having first and second dipole arms electrically coupled to respective first and second ports of a first common mode rejection filter. The first common mode rejection filter is configured such that a first impedance therein electrically coupled to the first port is equal to Z1, and a second impedance therein electrically coupled to the second port is equal to Z2, where: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); R1 and R2 are resistances of first and second inductors, respectively; Li and L2 are inductances of the first and second inductors, respectively; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second currents flowing into the first and second ports, respectively; and co is an angular frequency of the first and second currents. Additionally, the first common mode rejection filter can be integrated into a first feed stalk that: (i) is electrically coupled to a first end of the first dipole arm and a first end of the second dipole arm, and (ii) supports the first dipole radiator in front of a substrate (e.g., a ground plane reflector of a base station antenna).

[0015] According to yet other embodiments of the invention, an antenna is provided that includes a radiator (e.g., a loop dipole, a box dipole, etc.) and a feed stalk. This feed stalk, which is electrically coupled to the radiator by first and second feed paths, includes a common mode rejection filter having first and second ports electrically connected to the first and second feed paths, respectively. In some of these embodiments of the invention, a pair of coupled inductors is included in the common mode rejection filter, which can be disposed intermediate a base and a distal end of the feed stalk. The pair of inductors includes a first inductor having a first current carrying terminal electrically coupled to the first port of the common mode rejection filter, and a second inductor having a first current carrying terminal electrically coupled to the second port of the common mode rejection filter.

[0016] In some of these embodiments of the application, the feed stalk can include a printed circuit board having patterned metallization on first and second opposing faces thereof, and the pair of coupled inductors can be at least partially defined by the patterned metallization on the first and second opposing faces of the printed circuit board. Additionally, a first feed path can be electrically connected to a first inductor of the pair of coupled inductors, and a second feed path can be electrically connected to a second inductor of the pair of coupled inductors by a plated through hole in the printed circuit board.

[0017] An antenna according to another embodiment of the application includes a radiator, and a feed stalk having a common mode rejection (CMR) filter embedded therein. In some of these embodiments, the radiator includes first and second radiating arms (e.g., dipole arms) that are electrically coupled to respective first and second ports of the CMR filter. This CMR filter, which is located within a feed signal path of the antenna, is configured such that a first impedance therein is equal to Z1 and a second impedance therein is equal to Z2. The first impedance is electrically coupled to the first port, and the second impedance is electrically coupled to the second port. According to these embodiments: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); Li ~ L2; R1 and R2 are the resistances of the first and second inductors, respectively; Li and L2 are the inductances of the first and second inductors, respectively; M is the mutual inductance between the first and second inductors; I1 and I2 are first and second common mode currents flowing into the first and second ports, respectively; the symbol "~" designates equality within ±10%; co is the angular frequency of the first and second common mode currents; and M is sufficiently close in magnitude to Li and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at the angular frequency co.

[0018] According to some of the embodiments of the application, the feed signal path includes a double-sided printed circuit board (PCB) having a hook-shaped feed line on a first surface thereof. The first and second inductors can also be patterned as spiral inductors on a second surface of the PCB. And, these spiral inductors can be configured as mirror images of each other about a center line of the PCB across which the hook-shaped feed line can traverse. In some embodiments, the PCB includes a first electroplated via electrically connecting a first end of the first inductor to a first metallization pattern on the first surface of the PCB, and a second electroplated via electrically connecting a first end of the second inductor to a second metallization pattern on the first surface of the PCB. Based on this configuration of the PCB, a first radiating arm of the radiator can be electrically coupled by the first metallization pattern to a first port of the common mode rejection filter, and a second radiating arm of the radiator can be electrically coupled by the second metallization pattern to a second port of the common mode rejection filter. Additionally, a second end of the first inductor can be electrically connected to a third metallization pattern covering a majority of a first half of the second surface of the PCB, and a second end of the second inductor can be electrically connected to a fourth metallization pattern covering a majority of a second half of the second surface of the PCB.

[0019] In still further embodiments of the application, an antenna is provided that includes a radiator having a first radiating arm and a second radiating arm, and a feed stalk having a common mode rejection (CMR) filter therein. This CMR filter is configured such that a first impedance electrically coupled to the first radiating arm is equal to Z1, and a second impedance electrically coupled to the second radiating arm is equal to Z2. According to this embodiment, Z1 = R1 + jcoLi + jcoM(I2 / I1), and Z2 = R2 + jcoL2 + jcoM(I1 / I2), where: R1 and R2 are the resistances of the first and second inductors, respectively; Li and L2 are the inductances of the first and second inductors, respectively; and Li « L2; M is the mutual inductance between the first and second inductors; I1 and I2 are first and second common mode currents in the first and second impedances, respectively; co is the angular frequency of the first and second common mode currents; and the symbol "«" designates equality within ±25%.

[0020] In these embodiments, the first and second inductors can be spiral inductors configured as mirror images of each other about a centerline of the feed stalk. Additionally, a first end of the first inductor is electrically connected to a first electroplated via within the feed stalk that extends between the first end of the first inductor and the first radiating arm, and a first end of the second inductor is electrically connected to a second electroplated via within the feed stalk that extends between the first end of the second inductor and the second radiating arm. The feed stalk can also be configured as a double-sided printed circuit board having a hook-shaped feed line on a first surface thereof. The first and second inductors can also be patterned as spiral inductors on a second surface of the printed circuit board. Preferably, the mutual inductance M is sufficiently close in magnitude to LI and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at an angular frequency ω. BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1A is a schematic diagram of a multi-band radiator according to the prior art, including a high-band radiating element surrounded by a low-band box dipole radiating element, showing simulated differential mode and common mode currents therein.

[0022] FIG. IB shows differential mode (DM) and common mode (CM) radiation patterns of a box dipole antenna according to the prior art.

[0023] FIG. 2A shows a conventional box dipole radiating element with a tilted monopole, and simulated azimuthal radiation patterns with undesirable shoulders.

[0024] FIG. 2B shows a conventional metal plate box dipole radiating element with a tilted monopole, and simulated radiation patterns highlighting undesirable shoulders.

[0025] Figure 3A is a perspective view of a loop antenna having a feed stalk containing a common mode bandstop filter according to an embodiment of the present application.

[0026] Figure 3B is a perspective view of a feed stalk including a multi-layer printed circuit board (PCB) according to an embodiment of the present application.

[0027] Figure 3C is a perspective view of a loop antenna having a feed stalk containing a common mode bandstop filter according to an embodiment of the present application. Figure 3B is a front view of the feed stalk of

[0028] Figure 3D is a front view of the feed stalk of Figure 3B is a front view of the feed stalk of, but with all patterned metallization on the front side of the printed circuit board removed, leaving only the patterned metallization on the back side of the printed circuit board visible (seen through the PCB).

[0029] Figure 3E This is an embodiment of the present invention. Figure 3B The front view of the printed circuit board of the power supply handle shows a pair of plated through holes.

[0030] Figure 3F This is an embodiment of the present invention. Figure 3B A perspective view of the feed stem, but for illustrative purposes, a transparent printed circuit board is assumed so that the current path associated with the common-mode bandstop filter can be illustrated.

[0031] Figure 4 This is an application of the present invention. Figures 3B-3F A top-to-bottom plan view of a box-shaped dipole antenna with four feed handles.

[0032] Figure 5A This is a plan view of a multiband antenna, which includes: (i) a first outermost column and a second outermost column of a first cross-polarized dipole radiating element configured to operate in a first frequency band; (ii) a first innermost column and a second innermost column of a second cross-polarized dipole radiating element configured to operate in a second frequency band; and (iii) a first middle column and a second middle column of a third cross-polarized dipole radiating element configured to operate in a third frequency band, the third frequency band being lower than the first and second frequency bands.

[0033] Figure 5B It includes Figure 5A Plan view of the first and second intermediate columns of the single-band antenna of the third cross-polarized dipole radiating element.

[0034] Figure 5C is Figure 5A A side view of one of the second cross-polarized dipole radiating elements.

[0035] Figure 6A yes Figure 5A A graph of the -10dB beamwidth (in the azimuth plane) of the third cross-polarized dipole radiating element.

[0036] Figure 6B yes Figure 5B A graph of the -10dB beamwidth (in the azimuth plane) of the third cross-polarized dipole radiating element.

[0037] Figure 7A This is a side view of a cross-polarized dipole radiating element having first and second common-mode bandstop filters embedded in corresponding first and second feed handles (+45°, -45°) according to an embodiment of the present invention.

[0038] Figure 7B Embodiments of the present invention include Figure 7AFront and rear views of the first feed handle inside the radiating element.

[0039] Figure 7C Embodiments of the present invention include Figure 7A Front and rear views of the first feed handle inside the radiating element.

[0040] Figure 8 By using Figures 7A-7C The modified cross-polarized dipole radiator in Figure 5C is replaced by a cross-polarized dipole radiator. Figure 5A A graph of the -10dB beamwidth (in the azimuth plane) of the third cross-polarized dipole radiating element. Detailed Implementation

[0041] The invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are illustrated. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to all like elements.

[0042] 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 used only to distinguish one element from another. For example, without departing from the scope of the invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0043] It will be understood that when an element is described as being “on” another element, that element may be directly on the other element, or there may be intermediate elements. Conversely, when an element is described as being “directly on” another element, there are no intermediate elements. It will also be understood that when an element is described as being “connected” or “coupled” to another element, that element may be directly connected or coupled to the other element, or there may be intermediate elements. Conversely, when an element is described as being “directly connected” or “directly coupled” to another element, there are no intermediate elements. Other terms used to describe relationships between elements should be interpreted in a similar manner (i.e., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.).

[0044] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" can be used herein to describe a relationship of one element, layer, or region 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.

[0045] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including" when used 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.

[0046] Aspects and elements of all the embodiments disclosed below herein can be combined and / or combined with aspects or elements of other embodiments in any manner possible to provide additional embodiments.

[0047] Reference is now made to Figure 3A Antenna 30 according to embodiments of the present application is illustrated as including a shared single-side radiator segment 34a and a shared three-side radiator segment 34b, which extend along four sides of a rectangular (e.g., square) loop 34. As shown, the rectangular loop 34 is supported in front of a reflector surface 36 (e.g., ground plane) by a pair of "dual-path" feed stalks 32_1, 32_2. These feed stalks 32_1, 32_2 are each electrically coupled to respective ends of the radiator segments 34a, 34b, enabling the rectangular loop 34 to operate as a cross-polarized loop antenna. For example, when operating as an RF transmitter, the rectangular loop 34 is responsive to first and second "outbound" radio frequency (RF) signals, which are provided to first and second feed ports FEED1, FEED2 at base portions of the feed stalks 32_1, 32_2. Alternatively, when operating as a receiver of RF signals, the rectangular loop 34 receives and passes relatively low-energy RF signals to the feed stalks 32_1, 32_2, which are electrically coupled to low-noise amplification and receiver circuitry (not shown) at the first and second feed ports FEED1, FEED2. In some embodiments of the present application, the rectangular loop 34 can be a relatively small square loop, spanning about ¼ of a wavelength of the operating frequency of the antenna in each side.

[0048] Reference is now made to Figures 3B-3F By way of Figure 3AEach feed stalk 32_1, 32_2 used by the loop antenna of FIG. 1 can be configured as the same multi-layer printed circuit board (PCB) feed stalk 32. However, in alternative embodiments of the present invention, feed stalks having different impedances can be advantageous (e.g., for isolation or pattern adjustment purposes), thereby supporting unbalanced polarizations. In particular, and as shown in FIG. 2, the feed stalk 32 can include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on its first and second opposite faces. On the first face, a first conductive path 38a is provided, which includes a continuous metallization path extending from one corner at a first "distal" end of the substrate 42 to a diametrically opposite corner on a second end (e.g., base) of the substrate 42, as shown. In addition, a second conductive path is defined by patterned metal segments 38b, 38b' and 38c, as well as a pair of conductive (e.g., plated) vias 44a, 44b, which electrically connect the "middle" segment 38c to respective segments 38b and 38b'. Figure 3B As shown, the feed stalk 32 can include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on its first and second opposite faces. On the first face, a first conductive path 38a is provided, which includes a continuous metallization path extending from one corner at a first "distal" end of the substrate 42 to a diametrically opposite corner on a second end (e.g., base) of the substrate 42, as shown. In addition, a second conductive path is defined by patterned metal segments 38b, 38b' and 38c, as well as a pair of conductive (e.g., plated) vias 44a, 44b, which electrically connect the "middle" segment 38c to respective segments 38b and 38b'.

[0049] As shown, the feed stalk 32 can include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on its first and second opposite faces. On the first face, a first conductive path 38a is provided, which includes a continuous metallization path extending from one corner at a first "distal" end of the substrate 42 to a diametrically opposite corner on a second end (e.g., base) of the substrate 42, as shown. In addition, a second conductive path is defined by patterned metal segments 38b, 38b' and 38c, as well as a pair of conductive (e.g., plated) vias 44a, 44b, which electrically connect the "middle" segment 38c to respective segments 38b and 38b'. Figures 3C-3E As shown, the feed stalk 32 can include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on its first and second opposite faces. On the first face, a first conductive path 38a is provided, which includes a continuous metallization path extending from one corner at a first "distal" end of the substrate 42 to a diametrically opposite corner on a second end (e.g., base) of the substrate 42, as shown. In addition, a second conductive path is defined by patterned metal segments 38b, 38b' and 38c, as well as a pair of conductive (e.g., plated) vias 44a, 44b, which electrically connect the "middle" segment 38c to respective segments 38b and 38b'.

[0050] As now will be described more fully with reference to Figure 3B and 3F In particular, and as shown in FIG. 2, the first serpentine inductor 40a and the second serpentine inductor 40b extend on opposite first and second faces of the printed circuit board substrate 42, collectively defining a common mode rejection (CMR) filter 40 that selectively and advantageously rejects common mode current I CM From the feed port at the base of the feed stalk 32 to the radiator segments 34a, 34b within the rectangular loop 34, which are mounted to the distal end of the feed stalk 32 and are electrically connected to respective ones of the first conductive path 38a and the patterned metal segments 38b at the distal end. For example, with respect to the first feed port (FEED1) shown in FIG. 1, the CMR filter 40 rejects common mode current I Figure 3A As shown, the feed stalk 32 can include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on its first and second opposite faces. On the first face, a first conductive path 38a is provided, which includes a continuous metallization path extending from one corner at a first "distal" end of the substrate 42 to a diametrically opposite corner on a second end (e.g., base) of the substrate 42, as shown. In addition, a second conductive path is defined by patterned metal segments 38b, 38b' and 38c, as well as a pair of conductive (e.g., plated) vias 44a, 44b, which electrically connect the "middle" segment 38c to respective segments 38b and 38b'. CMpasses to the distal end portion of the first feed path 38a directly connected to the three-sided radiator segment 34b and blocks the common mode current I CM passes to the distal end portion of the second feed path 38b directly connected to the single-sided radiator segment 34a. Again, with respect to the second feed port (FEED2), the CMR filter 40 blocks the common mode current I CM passes to the distal end portion of the first feed path 38a directly connected to the single-sided radiator segment 34a and blocks the common mode current I CM passes to the distal end portion of the second feed path 38b directly connected to the three-sided radiator segment 34b.

[0051] These preferential RF “blocking” characteristics of the CMR filter 40 are best understood by considering the specific mutual inductance M between the overlapping, serpentine-shaped inductors 40a, 40b separated by the PCB substrate 42 having a predetermined thickness, can be designed in a manner that blocks the common mode current at the first RF frequency but selectively passes (with very low attenuation) the differential mode current at the same RF frequency.

[0052] While not wishing to be bound by any theory, the first inductor 40a on the first face 32’ of the substrate 42 can be considered to have an impedance Z1 and the second inductor 40b on the second face 32” of the substrate 42 can be considered to have an impedance Z2, where:

[0053] Z1 = R1 + jcoL1 + jcoM(I2 / I1); and

[0054] Z2 = R2 + jcoL2 + jcoM(I1 / I2).

[0055] In these equations, R1 and R2 are the resistances of the first inductor 40a and the second inductor 40b, respectively; L1 and L2 are the inductances of the first inductor 40a and the second inductor 40b, respectively; M is the mutual inductance between the overlapping first inductor 40a and the second inductor 40b separated from each other by the electrically insulating PCB substrate 42; I1 and I2 are the first and second currents, respectively, into the first port (1) and the second port (2) of the filter 40; and co is the angular frequency of the first and second currents. As shown by Figure 3F the first differential mode current I1 DM passes from the distal end portion of the first feed path 38a to the base portion of the first feed path 38a at the feed port, which is herein considered to be equal to I1, while I2 DM passes from the base portion of the second feed path (metal segment 38b’) to the distal portion of the second feed path (metal segment 38b), which is herein considered to be equal to -I2.

[0056] By carefully designing / adjusting inductors L1 and L2 (and their coupling) to be equal to each other and equal to their mutual inductance M (i.e., L1≈L2≈M, where the symbol “≈” indicates equality within ±10%), and regarding Figure 3F The differential mode current I1 shown DM and I2 DM Assuming I2 = -I1, then the impedances of the first inductor 40a and the second inductor 40b can be considered equal to:

[0057] Z1=R1+jω(L1–M)≈R1; and

[0058] Z2=R2+jω(L2–M)≈R2.

[0059] Therefore, since Z1≈R1 and Z2≈R2, the common-mode band-stop filter 40 presents a low resistive impedance to the differential-mode current, and this low impedance is equal to the DC resistance of inductors L1 and L2. However, regarding Figure 3F The common-mode current I shown CM Assuming I2 = I1, the impedances of the first inductor 40a and the second inductor 40b exhibit high (and frequency-dependent) inductive impedances in common-mode, thereby blocking common-mode current, where:

[0060] Z1=R1+jω(L1+M)≈R1+jω×2L; and

[0061] Z2=R2+jω(L2+M)≈R2+jω×2L.

[0062] Therefore, the handle-type common-mode bandstop filter 40 can be advantageously used to block common-mode current from passing through the feed handles 32_1, 32_2, thereby suppressing the common-mode current from the feed handles 32_1, 32_2. Figure 3A The monopole radiation of the ring radiator 34, otherwise it might appear on these feed handles.

[0063] According to another embodiment of the invention, the feed stem 32 and common-mode bandstop filter 40 described above can be applied to many other antenna designs that benefit from monopole radiation suppression caused by the generation of common-mode current within the radiating element. For example, as described by Figure 4 As shown, a box-shaped dipole antenna 50 (e.g., a metal plate box-shaped dipole antenna) can be configured with four "shared" dipole radiating elements 52a-52d, which together form four dipole radiators. The first dipole radiator is defined by radiating elements 52a and 52b, which are electrically coupled to a first feed handle 32_1 and a first feed port, the first feed port being coupled to the base of the first feed handle 32_1, as shown by... Figures 3B-3FAs shown above. Similarly, the second dipole radiator is defined by radiating elements 52b and 52c, which are electrically coupled to the second feed handle 32_2 and the second feed port. The third dipole radiator is defined by radiating elements 52c and 52d, which are electrically coupled to the third feed handle 32_3 and the third feed port. Finally, the fourth dipole radiator is defined by radiating elements 52d and 52a, which are electrically coupled to the fourth feed handle 32_4 and the fourth feed port. As mentioned above regarding Figures 3A-3F As described in the “loop” antenna 30, the first to fourth feed handles 32_1 to 32_4 enable differential-mode operation at each excited port of the box-type dipole antenna 50, but effectively block common-mode currents (and corresponding monopole radiation) on ports associated with opposite polarizations relative to each excited port. Furthermore, according to other embodiments of the invention, the feed handles described above can be applied to rectangular box-type dipole antennas, as well as antennas having dipole radiating elements of unequal lengths and / or spacing therebetween. Additionally, the feed handles and inductively coupled feed paths described herein can be advantageously used in many antenna designs where differential-mode signals are required and common-mode signals are not needed, such as, but not limited to, dipole antennas.

[0064] Referring now to 5A, a multi-band base station antenna 100a is shown comprising six (6) columns of radiating elements mounted on the front-facing surface of a ground plane reflector 102. These six columns include: (i) two innermost columns of radiating elements 104, which can be configured to operate in a relatively high first frequency band (e.g., 1695–2690 MHz); (ii) two outermost columns of radiating elements 106, which can be configured to operate in a relatively high second frequency band (e.g., 1427–2690 MHz); and (iii) two middle columns of larger radiating elements 108, which can be configured to operate in a lower third frequency band (e.g., 696–960 MHz).

[0065] like Figure 5A As shown in the plan view, each of the three types of radiating elements 104, 106, and 108 is configured as a corresponding dipole radiating element having two pairs of cross-polarized (e.g., -45°, +45°) radiating arms, which are supported in front of the reflector 102 by corresponding feed stem pairs. Furthermore, to achieve high integration within the base station antenna 100a, the smaller, relatively high-frequency band radiating elements 104, 106 utilize shorter feed stems, which allows these elements 104, 106 to be nested between the reflector 102 and the rearward surface of the larger radiating arms associated with the middle column of the radiating elements 108.

[0066] Unfortunately, this nesting of the relatively high band (HB) radiating elements 104, 106 in close proximity to the relatively low band (LB) radiating element 108 can result in unacceptable interference between the HB elements and the LB element, which interference is derived from a "induced" common mode resonance within the HB elements, which is indirectly derived from the differential mode radiation of the LB element in response to the feed signal provided to the LB element. While not wishing to be bound by any theory, the HB elements are typically shorter than the LB element, and their height can equal ¼λ of the frequency within the high end of the frequency band of the LB element. As will be appreciated by those skilled in the art, this "common mode" interference can result in a large unacceptable increase in the beamwidth of the LB element, as well as a degradation in gain and front-to-back ratio. Moreover, the use of conventional common mode filter techniques within the HB elements typically does not preclude the need to strike an appropriate compromise between matching within the HB elements and pushing any common mode resonance out of the frequency range of the LB element.

[0067] One example of a conventional HB element 104, which can be configured to operate in a relatively high first frequency band, is illustrated by FIG. 5C. As shown, a pair of orthogonally interconnected first and second feed legs 110a, 110b are provided, which are electrically coupled to a corresponding pair of radiating arms. In FIG. 5C, the first feed leg 110a is shown mechanically supporting a first pair of radiating arms 112a, 112b in front of the reflector 102. Among other things, this first feed leg 110a includes a first hook-shaped feed line 114a, which receives a corresponding cross-polarized feed signal, and a pair of serpentine inductors L1, L2 of a common mode filter, which extend adjacent to the outermost sides of the feed leg 110a. In the case where the first feed leg 110a is configured as a double-sided printed circuit board (PCB), the feed line 114a and inductors L1, L2 can be patterned on the opposite "front" and "back" surfaces of the PCB, along with other metallization (and metallized vias) to achieve proper matching.

[0068] While Figure 5A the configurations of the HB elements 104 of FIGS. 5A and 5C, a relatively large increase in the beamwidth of the LB element 108 within the multi-band antenna 100a can still occur when all of the radiating elements 104, 106 and 108 are simultaneously operating in their respective frequency bands. For example, as shown by the -10 dB beamwidth plots of FIG. 6A for the third cross-polarized dipole radiating element 108 of FIG. 5C, a sharp and unacceptable widening of the beamwidth occurs at relatively high frequencies, particularly at frequencies above 950 MHz. However, when the LB element 108 is operated alone (i.e., without the HB elements 104, 106), there is no such widening, as shown by the dedicated LB antenna 100b of FIG. 5B and the corresponding -10 dB beamwidth plots of FIG. 6B. Figure 6A Figure 5A As shown, the -10 dB beamwidth plots of FIG. 6A for the third cross-polarized dipole radiating element 108 of FIG. 5C illustrate that a sharp and unacceptable widening of the beamwidth occurs at relatively high frequencies, particularly at frequencies above 950 MHz. However, when the LB element 108 is operated alone (i.e., without the HB elements 104, 106), there is no such widening, as shown by the dedicated LB antenna 100b of FIG. 5B and the corresponding -10 dB beamwidth plots of FIG. 6B. Figure 5B Figure 6B As shown, the -10 dB beamwidth plots of FIG. 6A for the third cross-polarized dipole radiating element 108 of FIG. 5C illustrate that a sharp and unacceptable widening of the beamwidth occurs at relatively high frequencies, particularly at frequencies above 950 MHz. However, when the LB element 108 is operated alone (i.e., without the HB elements 104, 106), there is no such widening, as shown by the dedicated LB antenna 100b of FIG. 5B and the corresponding -10 dB beamwidth plots of FIG. 6B.​​

[0069] To address this limitation associated with the HB element 104 of Figure 5C, a cross-polarized dipole radiating element 204 is provided, comprising first and second feed stems (+45°, -45°), the first and second feed stems having highly mutually coupled first and second common-mode bandstop filters embedded therein. Figures 7A-7C As shown in the embodiment, this HB radiating element 204 includes a pair of positively interleaved first feed handles 210a and second feed handles 210b, which are mounted on the ground plane reflector 102 and receive corresponding feed signals (Feed1, Feed2) passing through it. These first and second feed handles 210a, 210b are also collectively configured to mechanically support the first and second pairs of dipole radiating arms thereon. Figure 7A As shown in the side view, the first feed handle 210a is electrically coupled to the corresponding first radiating arm 112a and second radiating arm 112b at the first port and the second port (Port1, Port2).

[0070] This first feed handle 210a is from Figure 7B A more detailed view is shown, illustrating front and rear views of a double-sided printed circuit board 212a with a metallized pattern thereon. Specifically, a first hook-shaped feed 214a is disposed on the front side of the board 212a. The first feed 214a is configured to receive a corresponding first feed signal (Feed1) at the base of the first board 212a, and the first feed extends through the ground plane reflector 102 during mounting. The first feed 214a also extends across the centerline (C / L) of the first board 212a and near the end of the main notch / slot 216a, as shown. The first feed handle 210a also includes a pair of closely spaced equivalent spiral inductors L1, L2 on the rear side of the board 212a. Advantageously, these spiral inductors L1, L2 are configured to have a high degree of mutual inductive coupling (M) therebetween, which helps to suppress the common-mode current (I1) within the first feed handle 210a. CM I2 CM In response to radiation received by radiating element 204, a common-mode current is induced in the first feed handle.

[0071] Specifically, according to some embodiments of the invention, the shape and close spacing of the "mirror-image" spiral inductors L1 and L2 are sufficient to generate a relatively high mutual inductance M, such that the mutual inductance with the suppressed first common-mode current I1 is... CM Second common-mode current I2 CM The associated return loss is greater than -6 dB at an angular frequency ω, which corresponds to a frequency that is typically located within a portion of a low-frequency band outside the relatively high-frequency band associated with the HB radiating element 204.

[0072] Additionally, each of the counterclockwise spiral inductor LI and the clockwise spiral inductor L2 terminate at respective electroplated vias 218 that provide conductive paths to the first and second ports Portl, Port2 of the first feed stalk 210a and the radiating arms 112a, 112b. As shown, these conductive paths include generally equal metallization patterns 222 on the front side of the board 212a that support the relative differential mode currents II DM , I2 DM during operation in the high frequency band. The back side of the board 212a also includes large area metal patterns 224 that support the differential mode currents II DM , I2 DM across the feed stalk 210a. Each of these metal patterns 224 covers most of one half of the back side of the board 212a and is electrically coupled to a corresponding metal pattern 226 on the front side of the board 212a by a plurality of electroplated vias PTH.

[0073] While not wishing to be bound by any theory, the illustrated overlap between the metal patterns 222 on the front side of the board 212 and the larger metal patterns 224 on the back side provides coupling within the built-in impedance matching circuit provided by the first feed stalk 210a. Additionally, the relatively large number of electroplated vias PTH support the creation of a grounded coplanar waveguide structure that can improve: (i) isolation between the two polarizations, (ii) cross-polarization radiation in the far field, and (iii) insertion loss.

[0074] Referring now to Figure 7C , the second feed stalk 210b is similarly shown as including a printed circuit board 212b having a second hook-shaped feed line 214b on a front side thereof. The second feed line 214b is configured to receive a corresponding second feed line signal (Feed2) at a base of the second board 212b, which second feed line extends through the ground plane reflector 102. The second feed line 214b also extends adjacent to a terminal end of a second notch / slot 216b that fits in an orthogonal relationship with the main notch / slot 216a when assembled. The second feed stalk 210b includes a pair of closely spaced spiral inductors LI and L2 on a back side of the board 212b. As described above with reference to Figure 7B , these spiral inductors LI and L2 are configured to have a high degree of mutual inductive coupling (M) therebetween that helps to suppress common mode currents (II CM , I2 CM ) that are "induced" within the second feed stalk 210b in response to low frequency band radiation from an adjacent radiating element, e.g. Figures 5A-5B .

[0075] As shown, each of the spiral inductors LI and L2 terminates at a respective electroplated via 218 that provides an electrically conductive path to the first port Portl and the second port Port2 of the second feed stalk 210b. These electrically conductive paths include a substantially equal metallization pattern 222 on the front side of the board 212b that supports opposite differential mode currents II DM , I2 DM during operation. The back side of the board 212b also includes a large area metal pattern 224 that supports differential mode currents II DM , I2 DM on the feed stalk 210b. Each of these metal patterns 224 is electrically coupled to a corresponding metal pattern 226 on the front side of the board 212b by a plurality of electroplated vias PTH.

[0076] Referring now to Figure 8 , there is provided a plot of the -10 dB beamwidth (in the azimuth plane) of the third cross-dipole radiating element of Figure 5A , which shows that substantial improvement in common mode (CM) interference can be achieved by replacing the second cross-dipole radiating element 104 of FIG. 5C with the HB cross-dipole radiating element 204 of Figures 7A-7C . While not wishing to be bound by any theory, it is believed that the shape and close spacing of the "mirror image" spiral inductors LI and L2 of Figures 7A-7C , which produces a relatively high mutual inductance M between LI and L2, achieves the high suppression of CM interference. According to some embodiments of the present application, this mutual inductance is sufficiently high that the return loss associated with the suppressed common mode currents (see, e.g., II CM , I2 CM in Figures 7B-7B is greater than -6 dB at the angular frequency ω of operation, which can correspond to frequencies within a portion of a low frequency band that is typically outside a relatively high frequency band associated with the HB radiating element 204.

[0077] In the drawings and specification, there have been disclosed typical preferred embodiments of the application, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the application being set forth in the following claims.

[0078] The present application also includes the following examples.

[0079] 1. An antenna, comprising:

[0080] A radiator including first and second radiator arms supported in front of a substrate by a feed stalk, the feed stalk including a first feed path electrically coupled to the first radiator arm, a second feed path electrically coupled to the second radiator arm, and a common mode rejection filter having first and second ports electrically connected to the first and second feed paths, respectively.

[0081] 2. The antenna of example 1, wherein the common mode rejection filter includes a pair of mutually coupled inductors.

[0082] 3. The antenna of example 2, wherein the pair of mutually coupled inductors are positioned intermediate a base and a distal end of the feed stalk.

[0083] 4. The antenna of example 2, wherein the pair of mutually coupled inductors includes a first inductor having a first current carrying terminal electrically coupled to the first port of the common mode rejection filter, and a second inductor having a first current carrying terminal electrically coupled to the second port of the common mode rejection filter.

[0084] 5. The antenna of example 3, wherein the feed stalk includes a printed circuit board having patterned metallization on first and second opposing faces of the printed circuit board; and wherein the pair of mutually coupled inductors are at least partially defined by the patterned metallization on the first and second opposing faces of the printed circuit board.

[0085] 6. The antenna of example 3, wherein the feed stalk includes a printed circuit board; wherein the pair of mutually coupled inductors includes a first inductor and a second inductor; wherein the first inductor is at least partially defined by patterned metallization on a first face of the printed circuit board; and wherein the second inductor is at least partially defined by patterned metallization on a second face of the printed circuit board opposite the first face.

[0086] 7. The antenna of example 6, wherein the first feed path is electrically connected to the first inductor; and wherein the second feed path is electrically connected to the second inductor by a plated through hole in the printed circuit board.

[0087] 8. The antenna of example 2, wherein the feed stalk includes a printed circuit board having patterned metallization on first and second opposing faces of the printed circuit board; and wherein the pair of mutually coupled inductors are at least partially defined by the patterned metallization on the first and second opposing faces of the printed circuit board.

[0088] 9. The antenna of example 2, wherein the feed stalk comprises a printed circuit board; wherein the pair of mutually coupled inductors comprises a first inductor and a second inductor; wherein the first inductor is defined at least in part by a patterned metallization on a first face of the printed circuit board; and wherein the second inductor is defined at least in part by a patterned metallization on a second face of the printed circuit board opposite the first face.

[0089] 10. The antenna of example 9, wherein the first feed path is electrically connected to the first inductor; and wherein the second feed path is electrically connected to the second inductor by a plated through hole.

[0090] 11. The antenna of example 4, wherein the common mode rejection filter is configured such that a first impedance electrically coupled to the first port is equal to Z1 and a second impedance electrically coupled to the second port is equal to Z2, wherein: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); R1 and R2 are the resistances of the first inductor and the second inductor, respectively; Li and L2 are the inductances of the first inductor and the second inductor, respectively; M is the mutual inductance between the first inductor and the second inductor; I1 and I2 are first and second currents flowing into the first port and the second port, respectively; and co is the angular frequency of the first and second currents.

[0091] 12. The antenna of example 11, wherein the antenna is a box dipole antenna having first through fourth feed ports; and wherein the first feed port is electrically coupled by the common mode rejection filter to the first feed path and the second feed path.

[0092] 13. The antenna of example 4, wherein the antenna is a box dipole antenna having first through fourth feed ports; and wherein the first feed port is electrically coupled by the common mode rejection filter to the first feed path and the second feed path.

[0093] 14. The antenna of example 1, wherein the antenna is a box dipole antenna having first through fourth feed ports; and wherein the first feed port is electrically coupled by the common mode rejection filter to the first feed path and the second feed path.

[0094] 15. The antenna of example 11, wherein the antenna is a loop antenna having at least a first feed port; and wherein the first feed port is electrically coupled by the common mode rejection filter to the first feed path and the second feed path.

[0095] 16. The antenna of example 4, wherein the antenna is a loop antenna having at least a first feed port; and wherein the first feed port is electrically coupled to the first feed path and the second feed path by the common mode rejection filter.

[0096] 17. The antenna of example 1, wherein the antenna is a loop antenna having at least a first feed port; and wherein the first feed port is electrically coupled to the first feed path and the second feed path by the common mode rejection filter.

[0097] 18. A box dipole antenna, comprising:

[0098] a first dipole radiator having first and second dipole arms electrically coupled to respective first and second ports of a first common mode rejection filter, the first common mode rejection filter configured such that a first impedance electrically coupled to the first port is equal to Z1, and a second impedance electrically coupled to the second port is equal to Z2, where: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); R1 and R2 are resistances of first and second inductors, respectively; Li and L2 are inductances of the first and second inductors, respectively; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second currents flowing into the first and second ports, respectively; and co is an angular frequency of the first and second currents.

[0099] 19. The antenna of example 18, wherein the first common mode rejection filter is integrated into a first feed stalk electrically coupled to a first end of the first dipole arm and a first end of the second dipole arm; and wherein the first feed stalk at least partially supports the first dipole radiator in front of an underlying substrate.

[0100] 20. The antenna of example 18, further comprising first through fourth feed stalks electrically coupled to first through fourth corners of the box dipole antenna, the first through fourth feed stalks including respective first through fourth common mode rejection filters integrated therein.

[0101] 21. The antenna of example 20, wherein the first through fourth common mode rejection filters have identical impedance characteristics.

[0102] 22. The antenna of example 19, wherein the first feed stalk comprises a printed circuit board; wherein the first inductor is defined at least in part by patterned metallization on a first face of the printed circuit board; and wherein the second inductor is defined at least in part by patterned metallization on a second face of the printed circuit board opposite the first face.

[0103] 23. The antenna of example 22, wherein the first dipole arm is electrically coupled to the first inductor; and wherein the second dipole arm is electrically coupled to the second inductor by a plated through hole in the printed circuit board.

[0104] 24. An antenna, comprising:

[0105] a radiator; and

[0106] a feed stalk comprising a common mode rejection filter having first and second ports electrically connected to first and second radiating elements within the radiator, respectively.

[0107] 25. The antenna of example 24, wherein the common mode rejection filter comprises a pair of mutually coupled inductors.

[0108] 26. The antenna of example 25, wherein the pair of mutually coupled inductors are disposed intermediate a top and a bottom of the feed stalk.

[0109] 27. The antenna of example 25, wherein the pair of mutually coupled inductors comprises a first inductor having a first current carrying terminal electrically coupled to a first port of the common mode rejection filter and a second inductor having a first current carrying terminal electrically coupled to a second port of the common mode rejection filter.

[0110] 28. The antenna of example 26, wherein the feed stalk comprises a printed circuit board having patterned metallization on first and second opposing faces of the printed circuit board; and wherein the pair of mutually coupled inductors are defined at least in part by the patterned metallization on the first and second opposing faces of the printed circuit board.

[0111] 29. The antenna of example 26, wherein the feed stalk comprises a printed circuit board; wherein the pair of mutually coupled inductors comprises a first inductor and a second inductor; wherein the first inductor is defined at least in part by patterned metallization on a first face of the printed circuit board; and wherein the second inductor is defined at least in part by patterned metallization on a second face of the printed circuit board opposite the first face.

[0112] 30. The antenna of example 29, wherein the first feed path is electrically connected to the first inductor, and the second feed path is electrically connected to the second inductor by plated through holes in the printed circuit board.

[0113] 31. The antenna of example 25, wherein the feed stalk comprises a printed circuit board having patterned metallization on first and second opposing faces of the printed circuit board; and wherein the pair of mutually coupled inductors are at least partially defined by the patterned metallization on the first and second opposing faces of the printed circuit board.

[0114] 32. The antenna of example 25, wherein the feed stalk comprises a printed circuit board; wherein the pair of mutually coupled inductors comprises a first inductor and a second inductor; wherein the first inductor is at least partially defined by patterned metallization on a first face of the printed circuit board; and wherein the second inductor is at least partially defined by patterned metallization on a second face of the printed circuit board opposite the first face.

[0115] 33. The antenna of example 32, wherein the first feed path is electrically connected to the first inductor, and the second feed path is electrically connected to the second inductor by plated through holes.

[0116] 34. The antenna of example 27, wherein the common-mode rejection filter is configured such that a first impedance electrically coupled to the first port is equal to Z1, and a second impedance electrically coupled to the second port is equal to Z2, wherein: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); R1 and R2 are the resistances of the first inductor and the second inductor, respectively; Li and L2 are the inductances of the first inductor and the second inductor, respectively; M is the mutual inductance between the first inductor and the second inductor; I1 and I2 are first and second currents flowing into the first port and the second port, respectively; and co is the angular frequency of the first and second currents.

[0117] 35. The antenna of any of examples 24-34, wherein the radiators are selected from box dipole radiators and loop radiators.

[0118] 36. An antenna, comprising:

[0119] a radiator electrically coupled to respective first and second ports of a common mode rejection filter disposed in a feed signal path of the antenna, the common mode rejection filter configured such that a first impedance electrically coupled to the first port is equal to Z1, and such that a second impedance electrically coupled to the second port is equal to Z2, where: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); M « Li « L2; R1 and R2 are resistances of first and second inductors, respectively; Li and L2 are inductances of the first and second inductors, respectively; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second currents flowing into the first and second ports, respectively; the symbol « designates equality within ±10%; and co is an angular frequency of the first and second currents.

[0120] 37. The antenna of example 36, wherein the common mode rejection filter is integrated into a feed stalk that is electrically coupled to the radiator and at least partially supports the radiator in front of an underlying substrate.

[0121] 38. The antenna of example 37, wherein the feed stalk comprises a printed circuit board; wherein the first inductor is at least partially defined by a patterned metallization on a first face of the printed circuit board; and wherein the second inductor is at least partially defined by a patterned metallization on a second face of the printed circuit board opposite the first face.

[0122] 39. The antenna of example 36, wherein the common mode rejection filter is integrated into a feed stalk that is electrically coupled to the radiator; wherein the feed stalk comprises a printed circuit board; wherein the first inductor is at least partially defined by a patterned metallization on a first face of the printed circuit board; and wherein the second inductor is at least partially defined by a patterned metallization on a second face of the printed circuit board opposite the first face.

[0123] 40. The antenna of any one of examples 36 to 39, wherein the radiator is selected from a box dipole radiator and a loop radiator.

[0124] 41. An antenna, comprising:

[0125] a radiator configured to receive first and second differential mode feed signals from respective first and second ports of a common mode rejection filter, the common mode rejection filter including first and second mutually coupled inductors.

[0126] 42. The antenna of example 41, wherein the first inductor and the second inductor are matched to have an equivalent inductance; and wherein a magnitude of mutual inductance between the first inductor and the second inductor is equal to the inductance of the first inductor and the second inductor.

[0127] 43. An antenna feed pole, comprising:

[0128] a printed circuit board having a common mode rejection filter embedded in the printed circuit board, the common mode rejection filter including a first port and a second port, a first inductor electrically coupled to the first port, and a second inductor electrically coupled to the second port.

[0129] 44. The antenna feed pole of example 43, wherein the common mode rejection filter is configured such that a first impedance electrically coupled to the first port is equal to Z1, and a second impedance electrically coupled to the second port is equal to Z2, wherein: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); M « L1 « L2; R1 and R2 are resistances of the first inductor and the second inductor, respectively; Li and L2 are inductances of the first inductor and the second inductor, respectively; M is a mutual inductance between the first inductor and the second inductor; I1 and I2 are first and second currents flowing into the first port and the second port, respectively; the symbol « designates equality within ±10%; and co is an angular frequency of the first and second currents when the antenna feed pole is implemented within an active antenna.

[0130] 45. A radiating element, comprising:

[0131] a cross-dipole radiator; and

[0132] a first feed stalk and a second feed stalk electrically coupled to the cross-dipole radiator and responsive to respective first and second radio frequency (RF) feed signals, the first and second feed stalks including respective first and second common mode rejection (CMR) filters therein, the first CMR filter including first and second impedances Z1 = R1 + jcoLi + jcoM(I2 / I1) and Z2 = R2 + jcoL2 + jcoM(I1 / I2), where Li and L2 are inductances of respective first and second inductors within the first feed stalk; Li « L2, where the symbol « designates equality within ±20%; R1 and R2 are resistances of the first and second inductors; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second common mode currents in the first feed stalk; co is an angular frequency of the first and second common mode currents; and M is sufficiently close in magnitude to Li and L2 that return loss associated with the first and second common mode currents is greater than -6 dB at the angular frequency co.

[0133] 46. The radiating element of example 45, wherein the first feed stalk includes a double-sided printed circuit board having a pair of side-by-side inductors on a first surface of the double-sided printed circuit board as Li and L2, and a feed trace with a U-shaped feed segment on a second surface of the printed circuit board.

[0134] 47. The radiating element of example 45, wherein the first feed stalk includes a first double-sided printed circuit board having a pair of side-by-side inductors on a first surface of the first double-sided printed circuit board as Li and L2, and a feed trace with a U-shaped feed segment on a second surface of the first double-sided printed circuit board; and wherein the second feed stalk includes a second double-sided printed circuit board having a pair of side-by-side inductors on a first surface of the second double-sided printed circuit board, and a feed trace with a U-shaped feed segment on a second surface of the second double-sided printed circuit board.

[0135] 48. The radiating element of example 45, wherein the first and second feed stalks include respective first and second double-sided printed circuit boards having complementary grooves interlocked with one another therein.

[0136] 49. The radiating element of example 45, wherein the first and second inductors Li and L2 are configured as first and second spiral inductors, respectively.

[0137] 50. The radiating element of example 49, wherein the first stem comprises a double-sided printed circuit board (PCB); wherein the first spiral inductor and the second spiral inductor are patterned on a first surface of the PCB; and wherein the first spiral inductor spirals inward in a counterclockwise direction and the second spiral inductor spirals inward in a clockwise direction.

[0138] 51. The radiating element of example 46, wherein LI and L2 are spiral inductors.

[0139] 52. The radiating element of example 51, wherein LI and L2 are patterned as mirror images of one another with respect to a central axis of the printed circuit board.

[0140] 53. The radiating element of example 52, wherein the first feed stem and the second feed stem comprise respective first and second double-sided printed circuit boards having complementary notches that interlock with one another along the central axis.

[0141] 54. A radiating element, comprising:

[0142] a radiator electrically coupled to first and second ports of a common mode rejection filter disposed in a feed signal path of the radiating element, the common mode rejection filter configured such that a first impedance electrically coupled to the first port is equal to Z1 and a second impedance electrically coupled to the second port is equal to Z2, wherein: Z1 = R1 + jcoLI + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); LI « L2; R1 and R2 are electrical resistances of first and second inductors, respectively; LI and L2 are inductances of the first and second inductors, respectively; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second common mode currents flowing into the first and second ports, respectively; the symbol “«” means equal within ±10%; co is an angular frequency of the first and second common mode currents; and M is sufficiently close in magnitude to LI and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at the angular frequency co.

[0143] 55. The radiating element of example 54, wherein the feed signal path comprises a double-sided printed circuit board (PCB) having a hook-shaped feed line on a first surface of the double-sided printed circuit board.

[0144] 56. The radiating element of example 54, wherein the first inductor and the second inductor are patterned on a second surface of the PCB.

[0145] 57. The radiating element of example 56, wherein the first inductor and the second inductor are spiral inductors.

[0146] 58. The radiating element of example 57, wherein the first inductor and the second inductor are configured to be mirror images of one another about a centerline of the PCB that the hook-shaped feedline traverses.

[0147] 59. The radiating element of example 58, wherein the PCB includes a first plated through hole that electrically connects a first end of the first inductor to a first metallization pattern on a first surface of the PCB; and wherein the PCB includes a second plated through hole that electrically connects a first end of the second inductor to a second metallization pattern on the first surface of the PCB.

[0148] 60. The radiating element of example 59, wherein a first radiating arm of the radiator is electrically coupled by the first metallization pattern to a first port of the common mode rejection filter; and wherein a second radiating arm of the radiator is electrically coupled by the second metallization pattern to a second port of the common mode rejection filter.

[0149] 61. The radiating element of example 60, wherein a second end of the first inductor is electrically connected to a third metallization pattern that covers a majority of a first half of the second surface of the PCB; and wherein a second end of the second inductor is electrically connected to a fourth metallization pattern that covers a majority of a second half of the second surface of the PCB.

[0150] 62. A radiating element, comprising:

[0151] a radiator having a first radiating arm and a second radiating arm; and

[0152] a feed stalk having a common mode rejection (CMR) filter therein, the CMR filter configured such that a first impedance electrically coupled to the first radiating arm is equal to Z1, and a second impedance electrically coupled to the second radiating arm is equal to Z2, where: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); Li ~ L2; R1 and R2 are resistances of a first spiral inductor and a spiral second inductor, respectively; Li and L2 are inductances of the first spiral inductor and the second spiral inductor, respectively; M is a mutual inductance between the first spiral inductor and the second spiral inductor; I1 and I2 are first and second common mode currents in the first impedance and the second impedance, respectively; co is an angular frequency of the first and second common mode currents; and the symbol “~” designates equality within ±25%.

[0153] 63. The radiating element of example 62, wherein the first spiral inductor and the second spiral inductor are configured to be mirror images of each other about a centerline of the feed stalk.

[0154] 64. The radiating element of example 63, wherein a first end of the first spiral inductor is electrically connected to a first electroplated via within the feed stalk, the first electroplated via extending between the first end of the first spiral inductor and the first radiating arm; and wherein a first end of the second spiral inductor is electrically connected to a second electroplated via within the feed stalk, the second electroplated via extending between the first end of the second spiral inductor and the second radiating arm.

[0155] 65. The radiating element of example 63, wherein the feed stalk is a double-sided printed circuit board having a hook-shaped feed line on a first surface of the double-sided printed circuit board; and wherein the first spiral inductor and the second spiral inductor are patterned on a second surface of the printed circuit board.

[0156] 66. The radiating element of example 65, wherein M is sufficiently close in magnitude to Li and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at the angular frequency co.

[0157] 67. The radiating element of example 66, wherein a first end of the first spiral inductor is electrically connected to a first electroplated via within the feed stalk, the first electroplated via extending between the first end of the first spiral inductor and the first radiating arm; and wherein a first end of the second spiral inductor is electrically connected to a second electroplated via within the feed stalk, the second electroplated via extending between the first end of the second spiral inductor and the second radiating arm.

[0158] 68. The radiating element of example 67, wherein a second end of the first spiral inductor is electrically connected to a metallized pattern covering a majority of a first half of a second surface of the PCB; and wherein a second end of the second spiral inductor is electrically connected to a metallized pattern covering a majority of a second half of the second surface of the PCB.

[0159] 69. A radiating element, comprising:

[0160] a radiator having a first radiating arm and a second radiating arm; and

[0161] a feed stalk having a common mode rejection (CMR) filter therein, the CMR filter configured such that a first impedance electrically coupled to the first radiating arm is equal to Z1, and a second impedance electrically coupled to the second radiating arm is equal to Z2, where: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); Li ~ L2; R1 and R2 are resistances of a first inductor and a second inductor, respectively; Li and L2 are inductances of the first inductor and the second inductor, respectively; M is a mutual inductance between the first inductor and the second inductor; I1 and I2 are first and second common mode currents in the first and second impedances, respectively; co is an angular frequency of the first and second common mode currents; the symbol “~” designates equality within ±25%; and M is sufficiently close in magnitude to Li and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at the angular frequency co.

[0162] 70. The radiating element of example 69, wherein the feed stalk comprises a double-sided printed circuit board (PCB) having a hook-shaped feed line on a first surface of the double-sided printed circuit board; and wherein the first and second inductors are configured as first and second spiral inductors on a second surface of the PCB.

[0163] 71. The radiating element of example 70, wherein the first inductor is electrically connected to the first radiating arm via a first metal trace on the first surface of the PCB, and the second inductor is electrically connected to the second radiating arm via a second metal trace on the first surface of the PCB.

[0164] 72. An antenna, comprising:

[0165] a radiator electrically coupled to a feed stalk having a common mode rejection (CMR) filter therein, the CMR filter configured to suppress common mode radiation from the radiator by providing a frequency dependent impedance to a pair of common mode currents within the feed stalk sufficient to increase return loss associated with the pair of common mode currents to a level greater than -6 dB over a frequency range including a frequency of the common mode radiation.

[0166] 73. The antenna of Example 72, wherein the feed stalk is a double-sided printed circuit board (PCB) having a feed line on a first surface of the double-sided printed circuit board; and wherein the CMR filter includes a pair of spiral inductors on a second surface of the PCB.

[0167] 74. The antenna of Example 72, wherein when the antenna is active and responsive to (i) at least a first RF feed signal at a frequency of the differential mode current, and (ii) radiation by an adjacent radiator responsive to at least a second RF feed signal at a frequency of the common mode radiation, the frequency of the common mode radiation is less than the frequency of the differential mode current within the CMR filter.

[0168] 75. An antenna comprising:

[0169] a reflector;

[0170] a first radiating element responsive to at least a first feed signal on the reflector;

[0171] a second radiating element responsive to at least a second feed signal on the reflector, the second radiating element comprising:

[0172] a radiator electrically coupled to a feed stalk having a common mode rejection (CMR) filter therein, the CMR filter configured to suppress common mode radiation from the radiator by providing a frequency dependent impedance to a pair of common mode currents within the feed stalk sufficient to increase return loss associated with the pair of common mode currents to a level greater than -6 dB over a frequency range including a frequency of the common mode radiation.

[0173] 76. The antenna of Example 75, wherein the pair of common mode currents are induced within the feed stalk responsive to differential mode radiation from the first radiating element.

Claims

1. A radiating element comprising: a cross-dipole radiator; and a first feed stalk and a second feed stalk, the first and second feed stalks electrically coupled to the cross-dipole radiator and responsive to respective first and second radio frequency (RF) feed signals, the first and second feed stalks including respective first and second common mode rejection (CMR) filters, the first CMR filter including first and second impedances Z1 = R1 + jcoLi + jcoM(I2 / I1) and Z2 = R2 + jcoL2 + jcoM(I1 / I2), where Li and L2 are inductances of respective first and second inductors within the first feed stalk; Li « L2, where the symbol "«" designates equality within ±20%; R1 and R2 are resistances of the first and second inductors; M is a mutual inductance between the first and second inductors; I1 and I2 are first and second common mode currents in the first feed stalk induced in response to radiation received by the radiating element in a first frequency band, the first frequency band being lower than and outside of a second frequency band associated with the radiating element; co is an angular frequency of the first and second common mode currents; and M is sufficiently close in magnitude to Li and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at an angular frequency co corresponding to a frequency within a portion of the first frequency band, wherein the first feed stalk includes a double-sided printed circuit board having a pair of side-by-side inductors on a first surface of the double-sided printed circuit board as Li and L2.

2. The radiating element of claim 1, wherein the double-sided printed circuit board includes a first double-sided printed circuit board and a feed trace with a U-shaped feed segment is provided on a second surface of the double-sided printed circuit board.

3. The radiating element of claim 2, wherein the second feed stalk includes a second double-sided printed circuit board having a pair of side-by-side inductors on a first surface of the second double-sided printed circuit board and a feed trace with a U-shaped feed segment on a second surface of the second double-sided printed circuit board.

4. The radiating element of claim 3, wherein the double-sided PCB includes a first double-sided PCB and the second feed stalk includes a second double-sided PCB, the respective first and second double-sided printed circuit boards having complementary grooves interlocked with each other.

5. The radiating element of claim 1, wherein the first and second inductors Li and L2 are configured as first and second spiral inductors, respectively.

6. The radiating element of claim 5, wherein the first spiral inductor and the second spiral inductor are patterned on a first surface of the double-sided printed circuit board; and wherein the first spiral inductor spirals inward in a counterclockwise direction and the second spiral inductor spirals inward in a clockwise direction.

7. The radiating element of claim 5, wherein LI and L2 are patterned as mirror images of each other with respect to a center axis of the double-sided printed circuit board.

8. The radiating element of claim 7, wherein the double-sided printed circuit board comprises a first double-sided printed circuit board and the second feed stalk comprises a second double-sided printed circuit board, and the double-sided printed circuit boards have complementary notches that interlock with each other along the center axis.

9. A radiating element, comprising: a radiator having a first radiating arm and a second radiating arm; and a feed stalk having a common mode rejection (CMR) filter therein, the CMR filter configured such that a first impedance electrically coupled to the first radiating arm is equal to Z1 and a second impedance electrically coupled to the second radiating arm is equal to Z2, wherein: Z1 = R1 + jcoLi + jcoM(I2 / I1); Z2 = R2 + jcoL2 + jcoM(I1 / I2); LI « L2; R1 and R2 are resistances of a first inductor and a second inductor, respectively; LI and L2 are inductances of the first inductor and the second inductor, respectively; M is a mutual inductance between the first inductor and the second inductor; I1 and I2 are first and second common mode currents in the first and second impedances, respectively, induced in response to radiation received by the radiating element in a first frequency band, the first frequency band being lower than and outside of a second frequency band associated with the radiating element; co is an angular frequency of the first and second common mode currents; the symbol "«" designates equality within ±25%; and M is sufficiently close in magnitude to LI and L2 such that return loss associated with the first and second common mode currents is greater than -6 dB at an angular frequency co corresponding to a frequency within a portion of the first frequency band, wherein the first and second inductors are configured as first and second spiral inductors side-by-side.

10. The radiating element of claim 9, wherein the feed stalk comprises a double-sided printed circuit board (PCB) having a hook-shaped feed line on a first surface of the double-sided printed circuit board.

11. The radiating element of claim 10, wherein the first inductor is electrically connected to the first radiating arm via a first metal trace on the first surface of the PCB and the second inductor is electrically connected to the second radiating arm via a second metal trace on the first surface of the PCB.

12. An antenna, comprising: ​ A radiator comprising a plurality of radiating arms electrically coupled to a common mode rejection (CMR) filter configured to suppress common mode radiation from the radiator by providing a frequency dependent impedance to a pair of common mode currents induced within the plurality of radiating arms in response to radiation received by the radiator in a first frequency band, the first frequency band being lower than and outside of a second frequency band associated with the radiator, the frequency dependent impedance being sufficient to increase return loss associated with the pair of common mode currents to a level greater than -6 dB over a range of frequencies including a frequency of the common mode radiation within a portion of the first frequency band, wherein the CMR filter comprises a pair of spiral inductors.

13. The antenna of claim 12, wherein the frequency of the common mode radiation is less than a frequency of a differential mode current within the CMR filter when the antenna is active and responsive to (i) at least a first RF feed signal at the frequency of the differential mode current within the CMR filter and (ii) radiation from an adjacent radiator in response to at least a second RF feed signal at the frequency of the common mode radiation.

14. An antenna comprising: a reflector; a first radiating element on the reflector, the first radiating element being responsive to at least a first feed signal, the first radiating element being associated with a first frequency band; a second radiating element on the reflector, the second radiating element being responsive to at least a second feed signal, the second radiating element being associated with a second frequency band, the first frequency band being lower than and outside of the second frequency band, the second radiating element comprising: a radiator comprising a plurality of radiating arms electrically coupled to a common mode rejection (CMR) filter configured to suppress common mode radiation from the radiator by providing a frequency dependent impedance to a pair of common mode currents induced within the plurality of radiating arms in response to radiation received by the radiator in the first frequency band, wherein the frequency dependent impedance is sufficient to increase return loss associated with the pair of common mode currents to a level greater than -6 dB over a range of frequencies including a frequency of the common mode radiation within a portion of the first frequency band; wherein the CMR filter comprises a pair of spiral inductors.

15. The antenna of claim 14, wherein the pair of common mode currents are induced within the plurality of radiating arms in response to differential mode radiation from the first radiating element.

16. The antenna of claim 14, wherein a portion of a first spiral inductor of the pair of spiral inductors is separated from a portion of a second spiral inductor of the pair of spiral inductors by a dielectric material extending therebetween.

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