DUAL-POLARIZED RADIATING ELEMENTS FOR BASE STATION ANTENNAS HAVING BUILT-IN STALK FILTERS THAT BLOCK COMMON MODE RADIATION PARASITICS

Abstract

An antenna includes a radiator that is electrically coupled to a feed stalk having a common-mode rejection (CMR) filter therein. The CMR filter is 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, which is sufficient to increase a return loss associated with the pair of common mode currents to a level of greater than −6 dB across a frequency range including a frequency of the common mode radiation.

Claims

1.-44. (canceled)

45. A radiating element, comprising: a cross-dipole radiator; and first and second feed stalks, which are electrically coupled to said cross-dipole radiator and responsive to respective first and second radio frequency (RF) feed signals, said first and second feed stalks comprising respective first and second common-mode rejection (CMR) filters therein, said first CMR filter including a first impedance Z.sub.1=R.sub.1+jωL.sub.1+jωM(I.sub.2/I.sub.1) and a second impedance Z.sub.2=R.sub.2+jωL.sub.2+jωM(I.sub.1/I.sub.2), where L.sub.1 and L.sub.2 are the inductances of respective first and second inductors within the first feed stalk; L.sub.1≈L.sub.2, where the expression “≈” designates an equality within ±20%; R.sub.1 and R.sub.2 are the resistances of the first and second inductors; M is a mutual inductance between the first and second inductors; I.sub.1 and I.sub.2 are first and second common mode currents in the first feed stalk; ω is the angular frequency of the first and second common mode currents; and M is sufficiently close in magnitude to L.sub.1 and L.sub.2 that a return loss associated with the first and second common mode currents is greater than −6 dB at the angular frequency ω.

46. The radiating element of claim 45, wherein the first feed stalk comprises a doubled-sided printed circuit board having a pair of side-by-side inductors, as L.sub.1 and L.sub.2, on a first surface thereof, and a feed trace with a U-shaped feed segment on a second surface thereof.

47. The radiating element of claim 45, wherein the first feed stalk comprises a first doubled-sided printed circuit board having a pair of side-by-side inductors, as L.sub.1 and L.sub.2, on a first surface thereof, and a feed trace with a U-shaped feed segment on a second surface thereof; and wherein the second feed stalk comprises a second doubled-sided printed circuit board having a pair of side-by-side inductors on a first surface thereof, and a feed trace with a U-shaped feed segment on a second surface thereof.

48. The radiating element of claim 45, wherein the first and second feed stalks comprise respective first and second double-sided printed circuit boards having complementary grooves therein that interlock with each other.

49. The radiating element of claim 45, wherein the first and second inductors L.sub.1 and L.sub.2 are configured as first and second spiral inductors, respectively.

50. The radiating element of claim 49, wherein the first stalk comprises a double-sided printed circuit board (PCB); wherein the first and second spiral inductors are patterned on a first surface of the PCB; and wherein the first spiral inductor spirals inward in a counter-clockwise direction and the second spiral inductor spirals inward in a clockwise direction.

51. The radiating element of claim 46, wherein L.sub.1 and L.sub.2 are spiral inductors.

52. The radiating element of claim 51, wherein L.sub.1 and L.sub.2 are patterned as mirror images of each other relative to a center axis of the printed circuit board.

53. The radiating element of claim 52, wherein the first and second feed stalks comprise respective first and second double-sided printed circuit boards having complementary grooves therein that interlock with each other along the center axis.

54.-68. (canceled)

69. A radiating element, comprising: a radiator having first and second radiating arms; and a feed stalk having a common-mode rejection (CMR) filter therein, said CMR filter configured so that a first impedance therein, which is electrically coupled to the first radiating arm, is equivalent to Z.sub.1, and a second impedance therein, which is electrically coupled to the second radiating arm, is equivalent to Z.sub.2, where: Z.sub.1=R.sub.1+jωL.sub.1+jωM(I.sub.2/I.sub.1); Z.sub.2=R.sub.2+jωL.sub.2+jωM(I.sub.1/I.sub.2); L.sub.1≈L.sub.2; R.sub.1 and R.sub.2 are the resistances of a first inductor and a second inductor, respectively; L.sub.1 and L.sub.2 are the inductances of the first inductor and the second inductor, respectively; M is a mutual inductance between the first and second inductors; I.sub.1 and I.sub.2 are the first and second common mode currents in the first impedance and the second impedance, respectively; ω is the angular frequency of the first and second common mode currents; the expression “=” designates an equality within ±25%; and M is sufficiently close in magnitude to L.sub.1 and L.sub.2 that a return loss associated with the first and second common mode currents is greater than −6 dB at the angular frequency ω.

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

71. The radiating element of claim 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.

72. An antenna, comprising: a radiator electrically coupled to a feed stalk having a common-mode rejection (CMR) filter therein, said CMR filter configured to suppress common mode radiation from said radiator by providing a frequency dependent impedance to a pair of common mode currents within the feed stalk, which is sufficient to increase a return loss associated with the pair of common mode currents to a level of greater than −6 dB across a frequency range including a frequency of the common mode radiation.

73. The antenna of claim 72, wherein the feed stalk is a dual-sided printed circuit board (PCB) having a feed line on a first surface thereof; and wherein the CMR filter comprises a pair of spiral inductors on a second surface of the PCB.

74. The antenna of claim 72, wherein the frequency of the common mode radiation is less than a frequency of differential mode currents 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 currents, and (ii) radiation from an adjacent radiator, which is responsive to at least a second RF feed signal at the frequency of the common mode radiation.

75. An antenna, comprising: a reflector; a first radiating element responsive to at least a first feed signal, on the reflector; a second radiating element responsive to at least a second feed signal, on the reflector, said second radiating element comprising: a radiator electrically coupled to a feed stalk having a common-mode rejection (CMR) filter therein, said CMR filter configured to suppress common mode radiation from said radiator by providing a frequency dependent impedance to a pair of common mode currents within the feed stalk, which is sufficient to increase a return loss associated with the pair of common mode currents to a level of greater than −6 dB across a frequency range including a frequency of the common mode radiation.

76. The antenna of claim 75, wherein the pair of common mode currents are induced within the feed stalk in response to differential mode radiation from said first radiating element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1A is a schematic diagram of a multi-band radiator including a high-band radiating element surrounded by a low-band box dipole radiating element, showing simulated differential mode and common mode currents therein, according to the prior art.

[0021] FIG. 1B illustrates differential mode (DM) and common mode (CM) radiation patterns for a box dipole antenna, according to the prior art.

[0022] FIG. 2A illustrates a conventional box dipole radiating element with slanted monopoles, and a simulated azimuth radiation pattern having undesired shoulders.

[0023] FIG. 2B illustrates a conventional sheet metal box dipole radiating element with slanted monopoles, and a simulated radiation pattern that highlights undesired shoulders.

[0024] FIG. 3A is perspective view of a loop antenna with feed stalks containing common-mode rejection filters, according to an embodiment of the present invention.

[0025] FIG. 3B is a perspective view of a feed stalk including a multi-layer printed circuit board (PCB), according to an embodiment of the present invention.

[0026] FIG. 3C is a front view of the feed stalk of FIG. 3B, which illustrates patterned metallization on a front side of a printed circuit board, according to an embodiment of the invention.

[0027] FIG. 3D is a front view of the feed stalk of FIG. 3B, but will all patterned metallization on the front side of the printed circuit board removed and only patterned metallization on a rear side of the printed circuit board visible (looking through the PCB), according to an embodiment of the present invention.

[0028] FIG. 3E is a front view of the printed circuit board of the feed stalk of FIG. 3B, which reveals a pair of plated through-holes, according to an embodiment of the present invention.

[0029] FIG. 3F is a perspective view of the feed stalk of FIG. 3B, but assuming a transparent printed circuit board for purposes of illustration so that current paths associated with the common-mode rejection filter can be illustrated, according to an embodiment of the invention.

[0030] FIG. 4 is a top-down plan view of a box dipole antenna that utilizes four of the feed stalks of FIGS. 3B-3F, according to an embodiment of the present invention.

[0031] FIG. 5A is a plan view of a multi-band antenna containing: (i) first and second outermost columns of first cross-polarized dipole radiating elements configured to operate in a first frequency band, (ii) first and second innermost columns of second cross-polarized dipole radiating elements configured to operate in a second frequency band, and (iii) first and second intermediate columns of third cross-polarized dipole radiating elements configured to operate in a third frequency band, which is lower than the first and second frequency bands.

[0032] FIG. 5B is a plan view of a single-band antenna containing the first and second intermediate columns of third cross-polarized dipole radiating elements of FIG. 5A.

[0033] FIG. 5C is a side view of one of the second cross-polarized dipole radiating elements of FIG. 5A.

[0034] FIG. 6A is a graph of −10 dB beamwidth (in the azimuth plane) for the third cross-polarized dipole radiating elements of FIG. 5A.

[0035] FIG. 6B is a graph of −10 dB beamwidth (in the azimuth plane) for the third cross-polarized dipole radiating elements of FIG. 5B.

[0036] FIG. 7A is a side view of a cross-polarized dipole radiating element with first and second common-mode rejection filters embedded within respective first and second feed stalks (+45°, −45°), according to an embodiment of the invention.

[0037] FIG. 7B includes front-side and back-side views of a first feed stalk within the radiating element of FIG. 7A, according to an embodiment of the invention.

[0038] FIG. 7C includes front-side and back-side views of a first feed stalk within the radiating element of FIG. 7A, according to an embodiment of the invention.

[0039] FIG. 8 is a graph of −10 dB beamwidth (in the azimuth plane) for the third cross-polarized dipole radiating elements of FIG. 5A, as modified by substituting the cross-polarized dipole radiating element of FIGS. 7A-7C for the second cross-polarized dipole radiating elements of FIG. 5C.

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] The present invention now will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being 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.

[0041] Like reference numerals refer to like elements throughout.

[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 only used to distinguish one element from another. 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.

[0043] 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 like fashion (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” may 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 invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” 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 of the embodiments disclosed hereinbelow can be combined in any way and/or combination with aspects or elements of other embodiments to provide a plurality of additional embodiments.

[0047] Referring now to FIG. 3A, an antenna 30 according to an embodiment of the invention is illustrated as including a shared single-sided radiator segment 34a and a shared three-sided radiator segment 34b, which extend along four sides of a rectangular (e.g., square) loop 34. As shown, this rectangular loop 34 is supported in front of a reflector surface 36, such as a ground plane, by a pair of “dual-path” feed stalks 32_1, 32_2. These feed stalks 32_1, 322, which are each electrically coupled to respective ends of the radiator segments 34a, 34b, enable operation of the rectangular loop 34 as a cross-polarized loop antenna. For example, when operating as an RF transmitter, the rectangular loop 34 is responsive to first and second “outgoing” radio frequency (RF) signals, which are provided to first and second feed ports FEED1, FEED2 at the base of the feed stalks 32_1, 32_2.

[0048] 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 at the first and second feed ports FEED1, FEED2 to low noise amplification and receiver circuitry (not shown). In some embodiments of the invention, the rectangular loop 34 may be a relatively small square loop with each side spanning about % of the wavelength for the operating frequency of the antenna.

[0049] Referring now to FIGS. 3B-3F, each of the feed stalks 32_1, 32_2 utilized by the loop antenna of FIG. 3A may be configured as identical multi-layer printed circuit board (PCB) feed stalks 32. However, in alternative embodiments of the invention, it may be advantageous (e.g., for isolation or pattern tuning purposes) to have feed stalks with different impedances to thereby support unbalanced polarizations. In particular, and as shown by FIG. 3B, the feed stalk 32 may include a dielectric (i.e., non-conductive) board substrate 42 having patterned metallization on first and second opposing sides thereof. On the first side, a first electrically conductive path 38a is provided, which includes a continuous metallization path that extends 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 illustrated. In addition, a second electrically conductive path is defined by patterned metal segments 38b, 38b′ and 38c and a pair of electrically conductive (e.g., plated) through-holes 44a, 44b, which electrically connect “intermediate” segment 38c to respective segments 38b and 38b′.

[0050] As shown more fully by FIGS. 3C-3E, a first side 32′ of the feed stalk 32 includes a serpentine-shaped inductor 40a, which extends in series within the first electrically conductive path 38a (without interruption) and at a location intermediate the ends of the substrate 42, as shown. In addition, the patterned metal segments 38b, 38b′ on the first side 32′ of the feed stalk 32, the two plated through-holes 44a, 44b, and the patterned metal segment 38c on the second side 32″ of the feed stalk 32, which includes a serpentine-shaped inductor 40b therein, collectively define a second electrically conductive path that extends between diametrically opposite corners of the feed stalk 32, as shown. According to alternative embodiments of the invention, the first and second electrically conductive paths (including inductors 40a, 40b) may be provided in the absence of a dielectric board substrate.

[0051] As will now be described more fully with respect to FIGS. 3B and 3F, the first and second serpentine-shaped inductors 40a, 40b, which extend on opposing first and second sides of the printed circuit board substrate 42, collectively define a common-mode rejection (CMR) filter 40 that selectively and advantageously blocks common mode currents I.sub.CM from passing from a feed port at the base of a feed stalk 32 to the radiator segments 34a, 34b within the rectangular loop 34, which are mounted to a distal end of the feed stalk 32 and electrically connected to respective ones of the first electrically conductive path 38a and patterned metal segment 38b at the distal end. For example, with respect to the first feed port (FEED1) illustrated by FIG. 3A, the CMR filter 40 blocks a common mode current I.sub.CM from passing to a distal portion of the first feed path 38a, which is directly connected to the three-sided radiator segment 34b, and blocks a common mode current I.sub.CM from passing to a distal portion of the second feed path 38b, which is directly connected to the one-sided radiator segment 34a. Likewise, with respect to the second feed port (FEED2), the CMR filter 40 blocks a common mode current I.sub.CM from passing to a distal portion of the first feed path 38a, which is directly connected to the one-sided radiator segment 34a, and blocks a common mode current I.sub.CM from passing to a distal portion of the second feed path 38b, which is directly connected to the three-sided radiator segment 34b.

[0052] These preferential RF “blocking” characteristics of the CMR filter 40 can be best understood by considering how a specific mutual inductance M between the overlapping serpentine-shaped inductors 40a, 40b, which are separated by a PCB substrate 42 having a predetermined thickness, can be designed to block common mode currents at a first RF frequency, yet selectively pass (with very low attenuation) differential-mode currents at the same RF frequency.

[0053] Although not wishing to be bound by any theory, the first inductor 40a on the first side 32′ of the substrate 42 may be treated as having an impedance Z.sub.1, and the second inductor 40b on the second side 32″ of the substrate 42 may be treated as having an impedance Z.sub.2, where:

Z.sub.1=R.sub.1+jωL.sub.1+jωM(I.sub.2/I.sub.1); and

Z.sub.2=R.sub.2+jωL.sub.2+jωM(I.sub.1/I.sub.2).

[0054] In these equations, R.sub.1 and R.sub.2 are the resistances of the first inductor 40a and the second inductor 40b, respectively; L.sub.1 and L.sub.2 are the inductances of the first inductor 40a and the second inductor 40b, respectively; M is a mutual inductance between the overlapping first and second inductors 40a, 40b, which are separated from each other by the electrically insulating PCB substrate 42; 11 and 12 are the first and second currents into the first and second ports (1) and (2) of the filter 40, respectively; and ω is the angular frequency of the first and second currents. As shown by FIG. 3F, a first differential mode current I1.sub.DM, which passes from a distal portion of the first feed path 38a to a base of the first feed path 38a at the feed port, is treated herein as equivalent to I.sub.1, whereas I2.sub.DM, which passes from a base portion (metal segment 38b′) of the second feed path (at the feed port) to a distal portion (metal segment 38b) of the second feed path, is treated herein as equivalent to −I.sub.2.

[0055] By carefully designing/tuning the inductors L.sub.1 and L.sub.2 (and their coupling) to be equivalent to each other and equivalent to the mutual inductance M between them (i.e., L.sub.1≈L.sub.2=M, where the expression “≈” designates an equality within +10%), and assuming I.sub.2=−I.sub.1 with respect to the differential mode currents I1.sub.DM and I2.sub.DM shown in FIG. 3F, then the impedances of the first and second inductors 40a, 40b may be treated as equivalent to:

Z.sub.1=R.sub.1+jω(L.sub.1−M)≈R.sub.1; and

Z.sub.2=R.sub.2+jω(L.sub.2−M)≈R.sub.2.

[0056] Thus, because Z.sub.1≈R.sub.1 and Z.sub.2=R.sub.2, the common-mode rejection filter 40 presents a low resistive impedance to differential mode current, and this low impedance is equal to the DC resistance of the inductors L.sub.1 and L.sub.2. However, assuming I.sub.2=I.sub.1 with respect to the common mode currents I.sub.CM shown in FIG. 3F, then the impedances of the first and second inductors 40a, 40b present a high (and frequency dependent) inductive impedance at common mode to thereby block common mode currents, where:

Z.sub.1=R.sub.1+jω(L.sub.1+M)≈R.sub.1+jω×2L; and

Z.sub.2=R.sub.2+jω(L.sub.2+M)≈R.sub.2+jω×2L.

[0057] Accordingly, the stalk-based common-mode rejection filter 40 may be utilized advantageously to block common mode currents from passing through the feed stalks 32_1 and 32_2 and thereby inhibit monopole-type radiation from the loop radiator 34 of FIG. 3A, which might otherwise occur on these feed stalks.

[0058] According to further embodiments of the invention, the feed stalk 32 and common-mode rejection filter 40 described hereinabove may be applied to many other antenna designs that may benefit from monopole-type radiation suppression resulting from the generation of common-mode currents within radiating elements. For example, as illustrated by FIG. 4, a box dipole antenna 50 (e.g., sheet metal box dipole antenna) may be provided having four “shared” dipole radiating elements 52a-52d, which collectively form four dipole radiators. A first dipole radiator is defined by radiating elements 52a, 52b, which are electrically coupled to a first feed stalk 32_1 and first feed port coupled to a base of the first feed stalk 32_1, as illustrated by FIGS. 3B-3F. Similarly, a second dipole radiator is defined by radiating elements 52b, 52c, which are electrically coupled to a second feed stalk 32_2 and a second feed port. A third dipole radiator is defined by radiating elements 52c, 52d, which are electrically coupled to a third feed stalk 32_3 and a third feed port. Finally, a fourth dipole radiator is defined by radiating elements 52d, 52a, which are electrically coupled to a fourth feed stalk 32_4 and a fourth feed port. As described hereinabove with respect to the “loop” antenna 30 of FIGS. 3A-3F, the first through fourth feed stalks 32_1 through 32_4 will enable differential mode operation on each excited port of the box dipole antenna 50, yet efficiently block common mode currents (and corresponding monopole radiation) on ports associated with an opposite polarization relative to each excited port. And, according to other embodiments of the invention, the feed stalks described hereinabove may be applied to rectangular-shaped box dipole antennas, and antennas with dipole radiating elements having unequal lengths and/or spacing therebetween. In addition, the feed stalks and inductively-coupled feed paths described herein can be used advantageously in many antenna designs in which a differential mode signal is desired and a common mode signal is not desired such as, but not limited to, dipole-type antennas.

[0059] Referring now to 5A, a multi-band base station antenna 100a is illustrated as including six (6) columns of radiating elements, which are mounted on a forward-facing surface of a ground plane reflector 102. These six columns include: (i) two innermost columns of radiating elements 104, which may 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 may be configured to operate in a relatively high second frequency band (e.g., 1427-2690 MHz), and (iii) two intermediate columns of larger radiating elements 108, which may be configured to operate in a lower third frequency band (e.g., 696-960 MHz).

[0060] As shown by the plan view of FIG. 5A, 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 respective pairs of feed stalks. Moreover, to achieve a high degree of integration within the base station antenna 100a, the smaller relatively high band radiating elements 104, 106 utilize shorter feed stalks, which allow for a nesting of these elements 104, 106 between the reflector 102 and the rear-facing surfaces of the larger radiating arms associated with the intermediate columns of radiating elements 108.

[0061] Unfortunately, this nesting of relatively high band (HB) radiating elements 104, 106 in close proximity to relatively low band (LB) radiating elements 108 can cause unacceptable interference between the HB elements and the LB elements, which stems from “induced” common mode resonance within the HB elements that is derived indirectly from differential mode radiation from the LB elements, which is responsive to feed signals provided to the LB elements. Although not wishing to be bound by any theory, HB elements are generally shorter than LB elements and their height may be equivalent to % A of a frequency within a high end of the frequency band of the LB elements. As will be understood by those skilled in the art, this “common mode” interference can cause a large and unacceptable increase in the beamwidth of the LB elements, and a worsening of gain and front-to-back ratio. Moreover, the use of conventional common mode filter techniques within an HB element typically does not preclude the need to achieve a proper tradeoff between matching within the HB element and pushing any common mode resonance out of the frequency range of the LB element.

[0062] One example of a conventional HB element 104, which may be configured to operate in the relatively high first frequency band, is illustrated by FIG. 5C. As shown, a pair of orthogonally interconnected first and second feed stalks 110a, 110b are provided, which are electrically coupled to corresponding pairs of radiating arms. In FIG. 5C, the first feed stalk 110a is shown as mechanically supporting a first pair of radiating arms 112a, 112b in front of the reflector 102. Among other things, this first feed stalk 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 outermost sides of the feed stalk 110a. In the event the first feed stalk 110a is configured as a dual-sided printed circuit board (PCB), the feed line 114a and inductors L1, L2 may be patterned on opposing “front” and “back” surfaces of the PCB along with other metallization (and metallized through-holes) to achieve proper matching.

[0063] Notwithstanding the configuration of the HB element 104 of FIGS. 5A and 5C, a relatively large increase in beamwidth of the LB elements 108 within the multi-band antenna 100a may still occur when all radiating elements 104, 106 and 108 are concurrently active in their respective frequency bands. For example, as shown by FIG. 6A, a graph of the −10 dB beamwidth (in the azimuth plane) for the third cross-polarized dipole radiating elements 108 of FIG. 5A demonstrates a dramatic and unacceptable widening of beamwidth at relatively high frequencies, particularly at frequencies above 950 MHz. But, this widening is not present when the LB elements 108 are operating in isolation (i.e., without HB elements 104, 106), as illustrated by the exclusively LB antenna 100b of FIG. 5B and corresponding −10 dB beamwidth graph of FIG. 6B.

[0064] To address this limitation associated with the HB element 104 of FIG. 5C, a cross-polarized dipole radiating element 204 is provided, which includes first and second feed stalks (+45°, −45°) having highly mutually coupled first and second common-mode rejection filters embedded therein. As shown by the embodiment of FIGS. 7A-7C, this HB radiating element 204 includes a pair of orthogonally interconnected first and second feed stalks 210a, 210b, which are mounted on a ground plane reflector 102 and receive respective feed signals (Feed1, Feed2) passing therethrough. These first and second feed stalks 210a, 210b are also collectively configured to mechanically support first and second pairs of dipole radiating arms thereon. As shown by the side view of FIG. 7A, the first feed stalk 210a is electrically coupled at first and second ports (Port1, Port2) to respective first and second radiating arms 112a, 112b.

[0065] This first feed stalk 210a is illustrated in greater detail by FIG. 7B, which shows front and rear side views of a double-sided printed circuit board 212a having metallization patterns thereon. In particular, a first hook-shaped feed line 214a is provided on the front side of the board 212a. The first feed line 214a is configured to receive a corresponding first feed signal (Feed1) at a base of the first board 212a, which, upon mounting, extends through the ground plane reflector 102. The first feed line 214a also extends across a centerline (C/L) of the first board 212a, and proximate a terminal end of a primary notch/slot 216a, as shown. The first feed stalk 210a also includes a pair of closely-spaced apart and equivalent spiral inductors L.sub.1 and L.sub.2 on a rear side of the board 212a. Advantageously, these spiral inductors L.sub.1 and L.sub.2 are configured to have a high degree of mutual inductive coupling (M) therebetween, which contributes to suppression of common-mode currents (I1.sub.CM, I2.sub.CM) within the first feed stalk 210a, which are induced therein in response to radiation received by the radiating element 204.

[0066] In particular, according to some embodiments of the invention, the shape and close spacing of the “mirror-image” spiral inductors L.sub.1 and L.sub.2 is sufficient to yield a relatively high mutual inductance M, such that a return loss associated with the suppressed first and second common mode currents I1.sub.CM, I2.sub.CM is greater than −6 dB at an angular frequency ω, which corresponds to a frequency within a portion of a low-band that is typically outside the relatively high-band associated with the HB radiating element 204.

[0067] In addition, each of the counter-clockwise spiral inductor L.sub.1 and clockwise spiral inductor L.sub.2 terminate at respective plated through-holes 218, which provide electrically conductive paths to the first and second ports Port1, Port2 of the first feed stalk 210a and radiating arms 112a, 112b. As shown, these electrically conductive paths include generally equivalent metallization patterns 222 on the front side of the board 212a, which support opposing differential mode currents I1.sub.DM, I2.sub.DM within the high-band during operation. The rear side of the board 212a also includes large area metal patterns 224, which support the differential mode currents I1.sub.DM, I2.sub.DM across the feed stalk 210a. Each of these metal patterns 224 covers a majority of one-half of the rear side of the board 212, and is electrically coupled by a plurality of plated through-holes PTHs to corresponding metal patterns 226 on the front side of the board 212a.

[0068] Although not wishing to be bound by any theory, the illustrated overlap between the metal patterns 222 on the front side and the larger metal patterns 224 on the rear side of the board 212 provide coupling within a built-in impedance matching circuit provided by the first feed stalk 210a. In addition, the relatively large number of plated through-holes PTHs support the creation of a grounded coplanar waveguide structure, which can improve: (i) the isolation between both polarizations, (ii) the cross-pol radiation in the far-field, and (iii) the insertion loss.

[0069] Referring now to FIG. 7C, the second feed stalk 210b is similarly illustrated 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 signal (Feed2) at a base of the second board 212b, which extends through the ground plane reflector 102. The second feed line 214b also extends proximate a terminal end of a secondary notch/slot 216b, which mates with the primary notch/slot 216a in an orthogonal relationship upon assembly. The second feed stalk 210b includes a pair of closely-spaced apart spiral inductors L1 and L2 on a rear side of the board 212b. As described above with respect to FIG. 7B, these spiral inductors L1 and L2 are configured to have a high degree of mutual inductive coupling (M) therebetween, which contributes to suppression of common-mode currents (I1.sub.CM, I2.sub.CM) that are “induced” within the second feed stalk 210b in response to low-band radiation from an adjacent radiating element(s), such as the LB elements 108 of FIGS. 5A-5B.

[0070] As shown, each of the spiral inductors L1 and L2 terminate at respective plated through-holes 218, which provide electrically conductive paths to the first and second ports Port1, Port2 of the second feed stalk 210b. These electrically conductive paths include generally equivalent metallization patterns 222 on the front side of the board 212b, which support opposing differential mode currents I1.sub.DM, I2.sub.DM during operation. The rear side of the board 212b also includes large area metal patterns 224, which support the differential mode currents I1.sub.DM, I2.sub.DM across the feed stalk 210b. Each of these metal patterns 224 is electrically coupled by a plurality of plated through-holes PTHs to corresponding metal patterns 226 on the front side of the board 212b.

[0071] Referring now to FIG. 8, a graph of the −10 dB beamwidth (in the azimuth plane) for the third cross-dipole radiating elements of FIG. 5A is provided, which shows that a substantial improvement in common mode (CM) interference can be achieved by substituting the HB cross-dipole radiating element 204 of FIGS. 7A-7C for the second cross-dipole radiating elements 104 of FIG. 5C. Although not wishing to be bound by any theory, this high degree of suppression of CM interference is achieved in response to the shape and close spacing of the “mirror-image” spiral inductors L.sub.1 and L.sub.2 of FIGS. 7A-7C, which yield a relatively high mutual inductance M between L.sub.1 and L.sub.2. According to some embodiments of the invention, this mutual inductance is sufficiently high that a return loss associated with the suppressed common mode currents (see, e.g., I1.sub.CM, I2.sub.CM in FIGS. 7B-7B) is greater than −6 dB at an angular frequency ω of operation, which may correspond to a frequency within a portion of a low-band that is typically outside the relatively high-band associated with the HB radiating element 204.

[0072] In the drawings and specification, there have been disclosed typical preferred embodiments of the invention 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 invention being set forth in the following claims.