Reference to Priority Application

[0001] This application claims priority to U.S. Provisional Application Serial No. 63/079,817, filed September 17, 2020, the disclosure of which is hereby incorporated herein by reference.

Field of the Invention

[0002] The present invention relates to radio communications and, more particularly, to radiating elements for base station antennas used in cellular communication systems.

Background

[0002] Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as "cells" which are served by respective base stations. The base station may include one or more antennas that are configured to provide two-way radio frequency ("RF") communications with mobile subscribers that are within the cell served by the base station. In many cases, each base station is divided into "sectors." In one common configuration, a hexagonally shaped cell is divided into three 120° sectors in the azimuth plane, and each sector is served by one or more base station antennas that have an azimuth Half Power Beamwidth ("HPBW") of approximately 65° to provide coverage to the full 120° sector. Typically, the base station antennas are mounted on a tower or other raised structure, with the radiation patterns (also referred to herein as "antenna beams") that are generated by the base station antennas directed outwardly. Base station antennas are often implemented as linear or planar phased arrays of radiating elements.

[0003] In order to accommodate the increasing volume of cellular communications, cellular operators have added cellular service in a variety of new frequency bands. While in some cases it is possible to use a single linear array of so-called "wideband" radiating elements to provide service in multiple frequency bands, in other cases it is necessary to use different linear arrays (or planar arrays) of radiating elements to support service in the different frequency bands.

[0004] As the number of frequency bands has proliferated, and increased sectorization has become more common (e.g., dividing a cell into six, nine or even twelve sectors), the number of base station antennas deployed at a typical base station has increased significantly. However, due to, for example, local zoning ordinances and/or weight and wind loading constraints for the antenna towers, there is often a limit as to the number of base station antennas that can be deployed at a given base station. In order to increase capacity without further increasing the number of base station antennas, so-called multi-band base station antennas have been introduced which include multiple arrays of radiating elements that operate in different frequency bands. One common multi-band base station antenna design includes two linear arrays of "low-band" radiating elements that are used to provide service in some or all of the 694-960 MHz frequency band and two linear arrays of "mid-band" radiating elements that are used to provide service in some or all of the 1427-2690 MHz frequency band. These linear arrays are typically mounted in side- by-side fashion on a common reflector. Conventional examples of radiating elements that may be used in multi-band base station antenna designs are disclosed in U.S. Patent No. 6,313,809 to Gabriel et al., entitled “Dual-Polarized Dipole Antenna”, and U.S. Patent Publication No. 2018/0269589 to Xu et al., entitled “Dual- Polarized Antenna.”

Summary of the Invention

[0005] A dual-polarized radiating element according to some embodiments of the invention can include four simultaneously excited folded dipoles that are capacitively loaded to each other and arranged into a wheel shape to thereby provide: (i) increased operating bandwidth because of improved impedance matching, (ii) low cross-polarization, (iii) reduced beam squint, (iv) reduced passive intermodulation (PIM) interference; and (v) symmetric and stable radiation (with relatively high isolation and low return loss) over a desired frequency band (e.g., 0.69 - 0.96 GHz) within a base station antenna. According to some of these embodiments of the invention, a four-post feed stalk is provided along with a first feed line, which is capacitively coupled to first and third posts of the feed stalk, and a second feed line, which is capacitively coupled to second and fourth posts of the feed stalk. A quad arrangement of folded dipole arms is also provided, which is configured as a generally wheel-shaped dual-polarized radiator that is mounted on and capacitively coupled to the feed stalk. In particular, each of the first, second, third and fourth folded dipole arms in the quad arrangement is capacitively coupled to a corresponding first, second, third and fourth post within the feed stalk.

[0006] In some of these embodiments of the invention, the first feed line is configured as a hook-shaped feed line, which includes a forward-extending outbound segment that extends adjacent the first post, a crossing segment that spans a gap between the first and third posts, and a rearwardly-extending return segment that extends adjacent the third post. Similarly, the second feed line is configured as a hook-shaped feed line, which includes a forward-extending outbound segment that extends adjacent the second post, a crossing segment that spans a gap between the second and fourth posts, and a rearwardly-extending return segment that extends adjacent the fourth post.

[0007] Advantageously, a first half of a first one of the folded dipole arms is capacitively loaded by “first” inter-arm metallization to a second half of a second one of the folded dipole arms, and a first half of the second one of the folded dipole arms is capacitively loaded by “second” inter-arm metallization to a second half of a third one of the folded dipole arms. Likewise, a first half of the third one of the folded dipole arms is capacitively loaded by “third” inter-arm metallization to a second half of a fourth one of the folded dipole arms, and a first half of the fourth one of the folded dipole arms is capacitively loaded by “fourth” inter-arm metallization to a second half of the first one of the folded dipole arms. And, according to some of these embodiments of the invention, a plurality of segments of the inter-arm metallization that extend between the first through fourth folded dipole arms also extend along respective concentric arcs having the same radius. The folded dipole arms and the inter-arm metallization may also be coplanar and formed as a single piece of stamped metallization (e.g., 0.8 mm sheet metal).

[0008] According to further embodiments of the invention, each of the folded dipole arms in the quad arrangement includes a pair of hatchet-shaped and radially diverging metal projections that are mirror images of each other. In particular, the hatchet-shaped and radially diverging metal projections within each pair face each other when viewed from a plan perspective. The hatchet-shaped and radially diverging metal projections within each pair may also be configured to converge into a proximal end of a corresponding folded dipole arm, which is spaced apart by a dielectric layer (e.g., 0.1 mm polythene gasket) from a distal end of a corresponding post within the feed stalk. In addition, a distal end of each of the folded dipole arms in the quad arrangement may also include a pair of closely spaced-apart and generally rectangular-shaped metallization patterns or a pair of interlocking combshaped (i.e. , meander-shaped) metallization patterns, which are coupled to distal ends of corresponding ones of the hatchet-shaped and radially diverging metal projections.

[0009] In some of these embodiments of the invention, the hatchet-shaped and radially diverging metal projections within each pair include elongate and arcuateshaped sides that converge into the proximal end of the corresponding folded dipole arm. And, a half of a first one of the folded dipole arms is capacitively loaded by inter-arm metallization to an immediately adjacent half of a second one of the folded dipole arms. In particular, a first portion of the inter-arm metallization may extend between: (i) an elongate and arcuate-shaped side of a hatchet-shaped and radially diverging metal projection within the half of the first one of the folded dipole arms, and (ii) an elongate and arcuate-shaped side of a hatchet-shaped and radially diverging metal projection within the half of the second one of the folded dipole arms. The first portion of the inter-arm metallization may also include a radially-inwardly extending metallization pattern having a pair of opposing sides that lie along respective convex arcs that are mirror images of each other. And, a radius of curvature of these convex arcs may be equivalent to a radius of curvature of the elongate and arcuate-shaped side of the hatchet-shaped and radially diverging metal projection within the half of the first one of the folded dipole arms.

[00010] In some further embodiments of the invention, the radially-inwardly extending metallization pattern includes a plurality of passive elements embedded therein. For example, a first portion of the inter-arm metallization may include a plurality of metallization patterns that define a series C-L-C-L-C circuit, whereas a second portion of the inter-arm metallization may include an L-C-L circuit in parallel with the C-L-C-L-C circuit. [00011] According to additional embodiments of the invention, a radiating element is provided, which includes a four-post feed stalk, a first feed line capacitively coupled to first and third posts of the feed stalk, and a second feed line capacitively coupled to second and fourth posts of the feed stalk. A quad arrangement of folded dipole arms are also provided, which are capacitively coupled to the feed stalk and capacitively loaded to each other by inter-arm metallization. This inter-arm metallization is configured to include a quad arrangement of radially-inwardly extending metal projections that respectively extend between corresponding pairs of the folded dipole arms. In some embodiments of the invention, a first one of the radially-inwardly extending metal projections includes: (i) a first plurality of metallization patterns that define a first series circuit having capacitive and inductive elements therein, and (ii) a second plurality of metallization patterns that define a second series circuit having capacitive and inductive elements therein, which extend in parallel with the first series circuit.

[00012] According to still further embodiments of the invention, a radiating element within a base station antenna may include a wheel-shaped dual-polarized radiator. This radiator may include a quad arrangement of folded dipole arms, which are capacitively loaded to each other by inter-arm metallization having a quad arrangement of radially-inwardly extending metal projections that are aligned to 12- o’ clock, 3 o’clock, 6 o’clock and 9 o’clock when viewed from a plan perspective.

Each one of these radially-inwardly extending metal projections can include: (i) a first plurality of metallization patterns that define a first series circuit having capacitive and inductive elements therein, and (ii) a second plurality of metallization patterns that define a second series circuit having capacitive and inductive elements therein, which are in parallel with the first series circuit. In addition, first, second, third and fourth ones of the folded dipole arms in the quad arrangement may be respectively aligned to 1 :30 o’clock, 4:30 o’clock, 7:30 o’clock and 10:30 o’clock when viewed from the same plan perspective. Advantageously, the quad arrangement of folded dipole arms and inter-arm metallization are defined from a single piece of stamped metallization. Brief Description of the Drawings

[00013] FIG. 1A is a perspective view of a capacitively-grounded wideband dualpolarized radiating element with wheel-shaped radiator, according to an embodiment of the invention.

[00014] FIG. 1 B is a plan view of the radiating element of FIG. 1 A.

[00015] FIGS. 1C-1 D are perspective views of the multi-post feed stalk of FIG. 1A, with first and second hook-shaped feed lines coupled thereto.

[00016] FIG. 2A is a partial front view of a base station antenna containing the wideband dual-polarized radiating element of FIGS. 1A-1 D, and a 2x2 array of relatively high band radiating elements therein, according to an embodiment of the invention.

[00017] FIG. 2B is an end view of the base station antenna of FIG. 2A, according to an embodiment of the invention.

[00018] FIG. 2C is an elevated partial side perspective view of the base station antenna of FIG. 2A, according to an embodiment of the invention.

[00019] FIG. 3 is a partial front view of a base station antenna containing a wideband dual-polarized radiating element and a 2x2 array of relatively high band radiating elements therein, according to an embodiment of the invention.

[00020] FIG. 4A is a plan view of a single piece wheel-shaped dual-polarized radiator with radio frequency (RF) cloaking, according to an embodiment of the invention.

[00021] FIG. 4B is a plan view of a single piece wheel-shaped dual-polarized radiator with RF cloaking, according to an embodiment of the invention.

Detailed Description of Embodiments

[00022] 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. Like reference numerals refer to like elements throughout. [00023] It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

[00024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprising", "including", "having" and variants thereof, when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. In contrast, the term "consisting of" when used in this specification, specifies the stated features, steps, operations, elements, and/or components, and precludes additional features, steps, operations, elements and/or components.

[00025] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[00026] Referring now to FIGS. 1A-1 D, a dual-polarized radiating element 100 according to an embodiment of the invention is illustrated as including a quad arrangement folded dipole radiating arms 102_1-102_4, which are arranged into a generally wheel-shaped cross-dipole configuration, as shown. This cross-dipole configuration also supports inter-arm capacitive (and inductive) loading using multisegment inter-arm metallization 104_1 -104_4, which extends between adjacent radiating arms 102_1 -102_4. A four-post feed stalk 20 is also provided, which extends between a rear facing side of the radiating arms 102_1-102_4 and a groundplane reflector 30, upon which the feed stalk 20 is mounted. As shown, a first hookshaped feed line 40 is provided, which originates through a first slot 32a in the reflector 30 and is capacitively coupled across respective air-gaps to first and third posts 22a, 22c of the feed stalk 20. In particular, this first hook-shaped feed line 40 includes a forward-extending outbound segment 40a that extends adjacent the first post 22a, a crossing segment 40b that spans an air gap between the first and third posts 22a, 22c, and a rearwardly-extending return segment 40c that extends adjacent the third post 22c. Similarly, a second hook-shaped feed line 42 is provided, which originates through a second slot 32b in the reflector 30 and is capacitively coupled across respective air-gaps to second and fourth posts 22b, 22d of the feed stalk 20. In particular, the second hook-shaped feed line 42 includes a forward-extending outbound segment 42a that extends adjacent the second post 22b, a crossing segment 42b that spans a gap between the second and fourth posts 22b, 22d, and a rearwardly-extending return segment 42c that extends adjacent the fourth post 22d. As illustrated by FIGS. 1C-1 D, these first through fourth posts 22a- 22d may be configured as identical metal posts, which are formed from stamped and bent sheet metal (with drilled through-holes for mounting). Likewise, the feed lines 40, 42 may also be formed from stamped sheet metal (e.g., 0.8 mm thick).

[00027] As shown by FIG. 1A, but omitted from FIGS. 1C-1 D, the spacings associated with the air gaps between the feed lines 40, 42 and the first through fourth posts 22a-22d are defined by a plurality of disc-shaped feed line mounting spacers/connectors 44 (e.g., polymer connectors), which attach on opposing sides to corresponding through-openings 46a within the first through fourth posts 22a-22d of the feed stalk 20, and corresponding through-openings 46b within the first and second feed lines 40, 42. As will be understood by those skilled in the art, these first and second feed lines 40, 42, which originate from radio frequency (RF) signal connectors (not shown) on a rear facing side of the reflector 30, provide first and second dual-polarized (e.g., +45°, -45°) feed signals to the folded dipole radiating arms 102_1 -102_4. In some embodiments of the invention, the RF signal connectors may be a low-PIM 4.3-10 type connector with RG402 coaxial cable. In addition, each of the feed lines 40, 42 and corresponding posts within the feed stalk 20 operate a respective air microstrip transmission lines.

[00028] As best shown by FIGS. 1 A-1 B, each of the first through fourth radiating arms folded dipole radiating arms 102_1 -102_4 is mounted to a corresponding one of the first though fourth posts 22a-22d of the feed stalk 20 using a corresponding pair of radiator mounting connectors 25. In some embodiments of the invention, these radiator mounting connectors 25 may be configured as polymer press-fit rivets (e.g., nylon press-fit rivets). As shown, a generally centrally located proximal end of each of the folded dipole radiating arms 102_1 -102_4 may include a corresponding multisided metal mounting plate 15 having a pair of drilled through-holes therein (not shown), through which the radiator mounting connectors 25 are inserted. As shown by FIGS. 1A and 1 D, during assembly of the radiating element 100, these four pairs of through-holes within the four centrally-located mounting plates 15 are aligned to corresponding pairs of through-holes 27a within six-sided mounting flanges 27 associated with distal ends of each of the first through fourth posts 22a-22d of the feed stalk 20. A layer of spacer material, such as a 0.1 mm thick polythene gasket 31 , is also applied as a capacitor dielectric layer, which extends between a forward facing surface of each of the six-sided mounting flanges 27 and corresponding rear facing surfaces of the metal mounting plates 15.

[00029] Similarly, as shown best by FIGS. 1 A and 1 C-1 D, four (4) reflector mounting connectors 35 (e.g., polymer press-fit rivets) may also be used to securely attach square-shaped mounting flanges 29 (with through-holes 29a therein) at proximal ends of the first through fourth posts 22a-22d of the feed stalk 20 to a forward facing surface 30a of the reflector 30, which has a corresponding quad arrangement of four through-holes (not shown) therein. A layer of spacer material, such as a 0.1 mm thick polythene gasket 33, is also applied as a capacitor dielectric layer between the reflector 30 and a rear facing surface of each of the square mounting flanges 29.

[00030] Referring again to the dual-polarized radiating element 100 of FIGS. 1A- 1 B, the four instances of inter-arm capacitive (and inductive) loading provided by the multi-segment inter-arm metallization 104_1-104_4 includes: (i) “first” inter-arm metallization 104_1 extending between a first half of the first one of the folded dipole arms 102_1 and a second half of the second one of the folded dipole arms 102_2; (ii) “second” inter-arm metallization 104_2 extending between a first half of the second one of the folded dipole arms 102_2 and a second half of the third one of the folded dipole arms 102_2; (iii) “third” inter-arm metallization 104_3 extending between a first half of the third one of the folded dipole arms 102_3 and a second half of the fourth one of the folded dipole arms 102_4; and (iv) “fourth” inter-arm metallization 104_4 extending between a first half of the fourth one of the folded dipole arms 102_4 and a second half of the first one of the folded dipole arms 102_1 . In addition, as shown best by FIG. 1 B, a plurality of outermost segments of the interarm metallization 104_1-104_4 that extend between the first through fourth folded dipole arms 102_1 -102_4 also extend along respective concentric arcs having the same radius (i.e., along a circle). The folded dipole arms 102_1 -102_4 and the interarm metallization 104_1-104_4 may also be coplanar and formed as a single piece of stamped metallization (e.g., 0.8 mm sheet metal), along with drilled through-holes (not shown), which receive radiator mounting connectors 25 during assembly. As described and illustrated more fully hereinbelow, the single piece of stamped metallization operates as a wheel-shaped dual-polarized radiator having a quad arrangement of folded dipole radiating arms 102_1 -102_4.

[00031] According to further embodiments of the invention, each of the folded dipole arms in the quad arrangement includes a pair of hatchet-shaped and radially diverging metal projections 106a, 106b that are mirror images of each other, and have inner and outer curved edges that trace concentric arcs (at a first radius R1 and a second radius R2, having magnitudes that impact matching in operating frequency). In particular, the hatchet-shaped and radially diverging metal projections 106a, 106b within each pair face each other when viewed from a plan perspective. As shown by FIGS. 1A-1 B, these hatchet-shaped and radially diverging metal projections 106a, 106b within each pair converge into a proximal end (e.g., mounting plate 15) of a corresponding folded dipole arm 102_1 -102_4. This convergence is provided by elongate and arcuate-shaped sides 10a, 10b that advantageously increase an effective electrical length of the folded dipole arms 102_1 -102_4. In addition, a distal end of each of the folded dipole arms 102_1-102_4 in the quad arrangement may also include a pair of closely spaced-apart and generally rectangular-shaped metallization patterns 108a, 108b, which are coupled to distal ends of corresponding ones of the hatchet-shaped and radially diverging metal projections 106a, 106b.

[00032] As further shown by FIGS. 1 A-1 B, a first portion 12 of the inter-arm metallization 104_1 may extend between: (i) an elongate and arcuate-shaped side 10a of a hatchet-shaped and radially diverging metal projection 106a within the half of the first one of the folded dipole arms 102_1 , and (ii) an elongate and arcuateshaped side 10b of a hatchet-shaped and radially diverging metal projection 106b within the half of the second one of the folded dipole arms 102_2. In particular, this first portion 12 of the inter-arm metallization 104_1 may be configured as a radially- inwardly extending metallization pattern having a pair of opposing sides that lie along respective convex arcs that are mirror images of each other. As shown, a radius of curvature of these convex arcs can be equivalent to a radius of curvature of the elongate and arcuate-shaped side 10a of the hatchet-shaped and radially diverging metal projection 106a within the corresponding half of the first one of the folded dipole arms 102_1 .

[00033] Accordingly, as illustrated best by FIG. 1 B, the wheel-shaped dualpolarized radiator within the radiating element 100 includes a quad arrangement of folded dipole arms 102_1-102_4, which are aligned to 10:30 o’clock, 1 :30 o’clock, 4:30 o’clock and 7:30 o’clock when viewed from a plan perspective. In addition, these dipole arms 102_1 -102_4 are capacitively loaded to each other by inter-arm metallization 104_1-104_4 having a quad arrangement of radially-inwardly extending metal patterns 12 that are aligned to 12-o’ clock, 3 o’clock, 6 o’clock and 9 o’clock when viewed from the same plan perspective.

[00034] Referring now to FIGS. 2A-2C, a base station antenna 200 according to another embodiment of the invention is illustrated as including an RF transparent housing 210 (e.g., radome), which encloses the dual-polarized radiating element 100 of FIGS. 1A-1 D. As shown, this radiating element 100 is mounted and generally centrally located on a forward facing surface of a ground plane reflector 220 having rearwardly extending RF chokes 222 on opposing sides thereof along with corresponding reflector-extending choke covers 224. In addition, floating metal strips 254 (with spaced openings therein), which are mounted on sidewalls of the housing 210, operate as azimuth beamwidth (AZBW) narrowing devices. [00035] In the event the dual-polarized radiating element 100 is configured to support a relatively low frequency band in a range from about 690 MHz to about 960 MHz, then the wheel-shaped arrangement of folded dipole radiating arms 102_1 - 102_4 may be mounted at a distance of about 80 mm in front of the reflector 220, which preferably has lateral dimensions of at least about 362 x 362 mm ² (i.e., A @ 827 MHz (mid band)). Advantageously, to provide efficient multi-band radiation, the base station antenna 200 is configured so that the feed stalk 20 of the radiating element 100 is aligned, on the reflector 220, to a geometric center of a 2x2 array of smaller and relatively high band radiating elements 250 (with beam focusing elements 252 thereon). Although not wishing to be bound by any theory, simulations of the radiating element 100 within the base station antenna 200 suggest a worst case return loss of better than about -14.8dB and a worst case isolation of better than about -22.3db, with a mean 3dB azimuth beamwidth of about 65.5° and a cross- polarization ratio (CPR) of about 20db (at boresight) and about 17.1 dB (at sector). [00036] Moreover, the dipole bandwidth associated with the radiating element 100 of FIGS. 2A-2C can likely be improved by using a meander-shaped gap within each of the folded dipole radiating arms 102_1-102_4 of a radiating element 100’. For example, as shown by the base station 200’ of FIG. 3, the single piece wheel-shaped radiator of FIGS. 1A-1 B and 2A-2C can be modified by replacing the generally rectangular-shaped metallization patterns 108a, 108b therein with a pair of meandershaped (e.g., interlocking comb-shaped) metallization patterns 108a’, 108b’, but otherwise maintaining the same configuration of the radiating arms 102_1-102_4 described hereinabove with respect to FIGS. 1A-1 B.

[00037] The above-described single piece wheel-shaped radiators associated with the radiating elements 100, 100’ described herein may be further modified as illustrated by FIGS. 4A-4B. In particular, FIG. 4A illustrates a wheel-shaped dualpolarized radiator 400 (without feed stalk mounting holes within a quad arrangement of mounting plates 15), which may be formed from a single piece of stamped metallization. And, relative to the wheel-shaped radiator described hereinabove with respect to FIGS. 1A-1 B, this wheel-shaped radiator 400 is modified to include additional metal meander lines and metal tabs that can be modeled as respective passive elements (e.g., inductors, capacitors), which advantageously support capacitive loading of the dipole arms and cloaking of RF signals outside a desired frequency band

[00038] Accordingly, as shown by FIG. 4A, the hatchet-shaped and radially diverging metal projections 106a, 106b of FIG. 1A-1 B have been modified as hatchet-shaped and radially diverging metal projections 106a’, 106b’, which are terminated by meander lines 107a, 107b and rectangular-shaped metallization patterns 108a, 108b, as shown. In addition, the radially-inwardly extending metal patterns 12 of FIG. 1A-1 B have been modified to include a plurality of meander lines and metal tabs that can be modeled as respective inductive and capacitive elements, which collectively define a parallel-connected circuit 12’ (within the inter-arm metallization 104_1’-104_4’). As shown, this circuit 12’ includes a series L-C-L circuit in parallel with a series C-L-C-L-C circuit. Likewise, as shown by FIG. 4B, a wheel-shaped radiator 400’ may be provided that includes all the metallization patterns within the radiator 400 of FIG. 4A, but with four additional pairs of metal tabs 410, which protrude radially outwardly from a generally-circular circumference of the wheel-shaped radiator 400’ and provide better impedance matching.

[00039] 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.