Patent Publication Number: US-9843108-B2

Title: Dual-feed dual-polarized antenna element and method for manufacturing same

Description:
This application claims the benefit of U.S. Provisional Application No. 62/029,296, filed on Jul. 25, 2014, entitled “Dual-Feed Dual-Polarized Antenna Element and Method for Manufacturing Same,” which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a dual-polarized antenna, and, in particular embodiments, to a dual-feed dual-polarized antenna element and method of manufacturing the same. 
     BACKGROUND 
     A variety of antennas are used in radar, telecommunications, and other radio frequency (RF) systems. One common type of antenna is a dipole antenna, the most common of which is the half-wave dipole antenna. A half-wave dipole antenna is formed by two quarter-wavelength conductors, or elements, placed back-to-back for a total length of one-half wavelength. A standing wave on an element of one-half wavelength in length yields the greatest voltage differential, as one end of the element is at a node of the wave, and the other is at an antinode of the wave. The larger the voltage differential between the dipole elements, the greater the current between the dipole elements. The current is distributed along the length of the dipole, causing it to radiate an electric field (E-field) and a magnetic field (H-field). The direction of the E-field, represented by an E-field vector, is referred to as the polarization of the antenna. 
     Some RF systems utilize dual-polarization, or dual-polarized, antennas. For example, in the telecommunications industry, dual-polarization antennas are often found in base-station systems. A dual-polarized antenna can radiate in two directions within the E-field plane (E-plane), sometimes referred to as the polarization plane. In each direction, the generated E-field is polarized from the other and the two polarizations are typically orthogonal in the E-plane. Orthogonal polarizations ideally prevent power from one polarization from bleeding into another, which, when measured, is referred to as cross-polarization isolation or cross-polarization discrimination. However, polarizations can vary from perfectly orthogonal and therefore create power inefficiencies in the RF system caused by power transfer between polarizations. 
     Dual-polarized dipole antennas can be formed by arranging two linear-polarized antenna elements in a way that creates dual polarization. For example, a dual-polarized dipole antenna can be formed with one dipole antenna element rotated 90 degrees in the E-plane from another dipole antenna element. Each polarization need not be vertical or horizontal, in fact, it is common in the telecommunications industry to use plus-or-minus 45 degree, or slant, polarization, where the 45 degree offset of each polarization is with respect to the vertical or horizontal. In certain RF systems, the dual-polarized dipole antenna is duplicated to form an array that allows multiple simultaneous transmission and reception. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a dual-polarized antenna having shared-element dipole antenna elements. In certain embodiments, the dual-polarized antenna is operable to produce stable azimuth beam width, high bandwidth, and good cross-polarization isolation in a small profile with the benefit of low cost manufacturing. 
     An embodiment dual-polarization antenna element includes four radiating elements and eight feed ports. The four radiating elements are arranged in a co-planar diamond pattern. The neighboring elements of the four radiating elements form four shared-element dipole antenna elements. Each of the four radiating elements is shared between two cross-polarized dipole antenna elements of the four shared-element dipole antenna elements. The eight feed ports are arranged in four cross-polarized dual-feed pairs respectively disposed on the four radiating elements. Each feed port on the four radiating elements excites at least one of the cross-polarized dipole antenna elements. 
     An embodiment dual-feed dual-polarized ultra wide band (UWB) antenna includes four radiating elements, a dual-feed network, and a circuit. The four radiating elements form four shared-element dipole antenna elements arranged in a co-planar diamond pattern. The four shared-element dipole antenna elements include two shared-element dipole antenna elements cross-polarized with respect to two others. Each shared-element dipole antenna element is composed of two radiating elements of the four radiating elements, and each of those two radiating elements is shared with a respective cross-polarized shared-element dipole antenna element of the four shared-element dipole antenna elements. The dual-feed network includes four feeds respectively coupled to neighboring pairs of radiating elements of the four radiating elements. Each of the four radiating elements is respectively coupled to two cross-polarized feeds of the four feeds. The circuit includes first and second dipole feed circuits respectively coupled to opposingly-arranged similarly-polarized feeds, of the four feeds. 
     An embodiment method for manufacturing a dual-feed dual-polarized antenna element includes forming four radiating elements and forming eight feed ports. The four radiating elements are arranged in a co-planar diamond pattern. The neighboring elements of the four radiating elements form four shared-element dipole antenna elements. Each of the four radiating elements is shared between two cross-polarized dipole antenna elements of the four shared-element dipole antenna elements. The eight feed ports are arranged in four cross-polarized dual-feed pairs respectively disposed on the four radiating elements. Each feed port on the four radiating elements is disposed to excite at least one of the cross-polarized dipole antenna elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of one embodiment of a wireless communication system; 
         FIG. 2  is an illustrative diagram of one embodiment of a dual-polarization antenna element; 
         FIG. 3  is an illustrative diagram of another embodiment of a dual-polarization antenna element; 
         FIG. 4  is an illustrative diagram of yet another embodiment of a dual-polarization antenna element; 
         FIG. 5  is an illustrative diagram of another embodiment of a dual-polarization antenna element; 
         FIGS. 6 -A and  6 -B are an illustrative diagram of one embodiment of a dual-feed network and a feed circuit; 
         FIG. 7  is an illustrative diagram of one embodiment of a dual-feed dual-polarized UWB antenna; 
         FIG. 8  is an illustrative diagram of another embodiment of a feed circuit; 
         FIG. 9  is an illustrative diagram of another embodiment of a dual-feed dual-polarized UWB antenna; 
         FIG. 10  is an illustrative diagram of another embodiment of a dual-feed dual-polarized UWB antenna; and 
         FIG. 11  is a flow diagram of one embodiment of a method of manufacturing a dual-feed dual-polarized antenna element. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of embodiments are discussed in detail below. It should be appreciated, however, the present disclosure provides many inventive concepts that may be embodied in a wide variety of contexts. The specific embodiments discussed herein are merely illustrative of ways to make and use various embodiments of this disclosure, and do not limit the scope of the disclosure. 
     Disclosed herein is an ultra wide band (UWB) dipole antenna with dual-polarization can be made with stable −3 dB azimuth beamwidth and good cross-polarization isolation. UWB antennas are used for transmitting over a large bandwidth, typically 500 megahertz (MHz) or larger. For a given frequency band, the wavelength is the wavelength for the center frequency in the band. Certain dipole antennas use two narrow quarter-wavelength conductors as elements, which yields a narrow bandwidth antenna. A UWB dipole antenna requires a larger antenna surface to achieve the wide bandwidth. The dual-polarized dual-fed UWB antenna element introduced herein uses quarter-wavelength elements having an area equal to a quarter-wavelength, or λ/4. Wavelength, λ, is defined as follows, 
               λ   =     C       f   center     ⁢       ɛ   eff             ,         
where, C is the speed of light, f center  is the center frequency of the band, and ∈ eff  is the effective dielectric constant for a given element. Additionally, it is realized herein, four dipole antenna elements can be provided with four radiating elements by forming shared-element dipole antenna elements. By reducing the typical element count from eight to four, fabrication, cost, and size can be reduced. A shared-element dipole antenna element excites each antenna element in such a way that current distribution over the radiating elements for each dipole does not bleed into the cross-polarized dipole. The shared-element dipole antenna element is fed by a dual-feed network that is operable to excite each radiating element for two orthogonal polarizations. The dual-feed network couples to the radiating elements via feed ports. It is realized herein the location of the feed ports on the radiating elements is a function of the wavelength and target impedance of the elements.
 
       FIG. 1  is a block diagram of one embodiment of a wireless communication system  100 . Wireless communication system  100  includes a base station  110  within which the dual-feed dual-polarization UWB antenna element introduced herein may be embodied. Base station  110  serves one or more User Equipment (UE) devices, such as UE  120 , UE  130 , UE  140 , and UE  150 , by receiving communications originating from the UE devices and forwarding the communications to their respective intended destinations, or by receiving communications destined for the UE devices and forwarding the communications to their respective intended UE devices. Some UE devices can communicate directly with one another as opposed to communicating through base station  110 . For example, in the embodiment of  FIG. 1 , a UE  160  transmits directly to UE  150 , and vice versa. Base station  110  is sometimes referred to as an access point, a NodeB, an evolved NodeB (eNB), a controller, or a communication controller. UEs  120  through  160  are sometimes referred to as stations, mobile stations, mobiles, terminals, users, or subscribers. 
       FIG. 2  is an illustrative diagram of one embodiment of a dual-polarization antenna element  200 . Antenna element  200  includes four radiating elements: element  210 - 1 , element  210 - 2 , element  210 - 3 , and element  210 - 4 . Antenna element  200  also includes eight feed ports, port  220 - 1  through port  220 - 8 . 
     The four radiating elements are arranged in a co-planar diamond pattern. The plane of the diamond pattern is also the plane of the E-field, or the E-plane. The E-plane is also referred to as the polarization plane. The four radiating elements are circle-shaped and sized according to the wavelength of antenna element  200 . The four radiating elements are quarter-wavelength elements, such that a dipole antenna element containing two radiating elements is a half-wavelength dipole antenna element. The size of each of the four radiating elements can be computed such that the area of each radiating element is equal to λ/4. Neighboring pairs of the four radiating elements form shared-element dipole antenna elements. Element  210 - 1  neighbors element  210 - 2  and element  210 - 4 . Element  210 - 1  and element  210 - 2  form shared-element dipole antenna element  230 - 1 . Likewise, element  210 - 2  and element  210 - 3  form shared-element dipole antenna element  230 - 2 , element  210 - 3  and element  210 - 4  form shared-element dipole antenna element  230 - 3 , and element  210 - 4  and element  210 - 1  form shared-element dipole antenna element  230 - 4 . Each of the four radiating elements is shared between two cross-polarized shared-element dipole antenna elements. For example, element  210 - 3  is shared between shared-element dipole antenna element  230 - 2  and shared-element dipole antenna element  230 - 3 . Shared-element dipole antenna element  230 - 2  is polarized roughly 45 degrees clockwise from vertical. Shared-element dipole antenna element  230 - 3  is polarized roughly −45 degrees clockwise from vertical, or 45 degrees counter-clockwise. The two elements are orthogonally polarized, or cross-polarized. Furthermore, antenna element  200  includes two shared-element dipole antenna elements that are cross-polarized with respect to the other two shared-element dipole antenna elements. In the embodiment of  FIG. 2 , shared-element dipole antenna elements  230 - 2  and  230 - 4  are cross-polarized with respect to shared-element dipole antenna elements  230 - 1  and  230 - 3 . In alternative embodiments, polarizations may be rotated toward the vertical or toward the horizontal. However, the dual-polarization should be orthogonal. 
     Feed ports  220 - 1  through  220 - 8  are arranged in cross-polarized dual-feed pairs. The four cross-polarized dual-feed pairs are port  220 - 1  and  220 - 2 , port  220 - 3  and  220 - 4 , port  220 - 5  and  220 - 6 , and port  220 - 7  and  220 - 8 . Each cross-polarized dual-feed pair is disposed on one of the four radiating elements. Port  220 - 1  and  220 - 2  are disposed on element  210 - 1 , port  220 - 3  and  220 - 4  are disposed on element  210 - 2 , port  220 - 5  and  220 - 6  are disposed on element  210 - 3 , and port  220 - 7  and  220 - 8  are disposed on element  210 - 4 . Feed ports  220 - 1  through  220 - 8  are operable to excite each of the four radiating elements of antenna element  200 . Each feed port of the cross-polarized dual-feed pair is configured to excite its respective radiating element for a cross-polarized one of the shared-element dipole antenna elements. For example, in the embodiment of  FIG. 2 , consider element  210 - 2 , on which feed port  220 - 3  and feed port  220 - 4  are disposed. Element  210 - 2  is an element of shared-element dipole antenna element  230 - 1  and shared-element dipole antenna element  230 - 2 . Feed port  220 - 3  is operable to excite element  210 - 2  for shared-element dipole antenna element  230 - 2 . Likewise, feed port  220 - 4  is operable to excite element  210 - 2  for shared-element dipole antenna element  230 - 1 . These excitations are cross-polarized, as are shared-element dipole antenna element  230 - 1  and shared-element dipole antenna element  230 - 2 . In the embodiment of  FIG. 2 , the feed ports are rectangular contacts suitable for a connection to a PCB feed network. In alternative embodiments, the feed ports can be circular and better suited for coaxial connection to a feed network. 
     Continuing the embodiment of  FIG. 2 , each of the shared-element dipole antenna elements is excited by two feed ports of feed ports  220 - 1  through  220 - 8 . Shared-element dipole antenna element  230 - 1 , having element  210 - 1  and element  210 - 2 , is configured to be excited through feed port  220 - 1  and  220 - 4 . Shared-element dipole antenna element  230 - 2 , having element  210 - 2  and element  210 - 3 , is configured to be excited through feed port  220 - 3  and  220 - 6 . Shared-element dipole antenna element  230 - 3 , having element  210 - 3  and element  210 - 4 , is configured to be excited through feed port  220 - 5  and  220 - 8 . Finally, shared-element dipole antenna element  230 - 4 , having element  210 - 4  and element  210 - 1 , is configured to be excited through feed port  220 - 7  and  220 - 2 . 
     The location of each of feed ports  220 - 1  through  220 - 8  on their respective radiating elements is determined according to the wavelength for antenna element  200  and the target impedance for each radiating element. The distance between feed ports within a shared-element dipole antenna element can, in one embodiment, be calculated according to the dimensions of the radiating elements, which is a function of the λ/4 element area and the element shape, and the spacing between neighboring radiating elements. Neighboring radiating elements, for example element  210 - 2  and  210 - 3 , are spaced such that their common feed ports, feed port  220 - 4  and feed port  220 - 5 , achieve the target impedance for the radiating elements when connected to a feed network. In the embodiment of  FIG. 2 , feed port  220 - 4  and feed port  220 - 5  are separated by λ/32. The same is true for feed ports  220 - 6  and  220 - 7 , feed ports  220 - 8  and  220 - 1 , and feed ports  220 - 2  and  220 - 3 . 
       FIG. 3  is an illustrative diagram of another embodiment of a dual-polarization antenna element  300 . Antenna element  300  operates like antenna element  200  of  FIG. 2 , and is similar in shape. Antenna element  300  includes four radiating elements: element  310 - 1 , element  310 - 2 , element  310 - 3 , and element  310 - 4 . Additionally, antenna element  300  includes feed ports  220 - 1  through  220 - 8  of  FIG. 2 . The four radiating elements of antenna element  300  are arranged in a co-planar diamond pattern, as is the case in the embodiment of  FIG. 2 . The four radiating elements are circular-ring shaped, having a conductive outer ring and a dielectric inner. In certain embodiments the dielectric inner is a PCB substrate. In other embodiments the dielectric inner can be air. The respective areas of each of the conductive outer rings of the four radiating elements are equal to λ/4. Feed ports  220 - 1  through  220 - 8  are disposed on the conductive outer rings of the four radiating elements. Feed ports  220 - 1  and  220 - 2  are disposed on element  310 - 1 , feed ports  220 - 3  and  220 - 4  are disposed on element  310 - 2 , feed ports  220 - 4  and  220 - 6  are disposed on element  310 - 3 , and feed ports  220 - 7  and  220 - 8  are disposed on element  310 - 4 . 
       FIG. 4  is an illustrative diagram of yet another embodiment of a dual-polarization antenna element  400 . Antenna element  400  operates like antenna element  200  of  FIG. 2  and antenna element  300  of  FIG. 3 . Similar in shape to antenna element  300 , antenna element  400  includes four radiating elements: element  410 - 1 , element  410 - 2 , element  410 - 3 , and element  410 - 4 . Antenna element  400  also includes feed ports  220 - 1  through  220 - 8  of  FIGS. 2 and 3 . The four radiating elements of antenna element  400  are arranged in a co-planar diamond pattern, as is the case in the embodiments of  FIGS. 2 and 3 . The four radiating elements are square-ring shaped, having a conductive outer ring and a dielectric inner, similar to those of the embodiment of  FIG. 2 . The respective volumes of each of the conductive outer rings of the four radiating elements are equal. Feed polls  220 - 1  through  220 - 8  are disposed on the conductive outer rings of the four radiating elements. Feed polls  220 - 1  and  220 - 2  are disposed on element  410 - 1 , feed polls  220 - 3  and  220 - 4  are disposed on element  410 - 2 , feed ports  220 - 5  and  220 - 6  are disposed on element  410 - 3 , and feed ports  220 - 7  and  220 - 8  are disposed on element  410 - 4 . 
       FIG. 5  is an illustrative diagram of another embodiment of a dual-polarization antenna element  500 . Antenna element  500  operates like antenna element  200  of  FIG. 2 , antenna element  300  of  FIG. 3 , and antenna element  400  of  FIG. 4 . Antenna element  500  includes four radiating elements: element  510 - 1 , element  510 - 2 , element  510 - 3 , and element  510 - 4 . The four radiating elements are teardrop shaped and arranged in a co-planar diamond pattern similar to those of the embodiments of  FIGS. 2, 3, and 4 . Each of the four radiating elements includes a narrow end opposite a bulbous end. The four radiating elements are disposed such that the respective narrow ends point toward the center of the co-planar diamond pattern. 
     Antenna element  500  also includes eight round feed ports arranged in dual-feed pairs, each dual-feed pair being disposed on a respective radiating element of the four radiating elements. Disposed on element  510 - 1  are feed ports  520 - 1  and  520 - 2 , disposed on element  510 - 2  are feed ports  520 - 3  and  520 - 4 , disposed on element  510 - 3  are feed ports  520 - 5  and  520 - 6 , and disposed on element  510 - 4  are feed ports  520 - 7  and  520 - 8 . The eight round feed ports operate like the rectangular feed ports of the embodiments of Figurers  2 ,  3 , and  4 . Feed ports  520 - 1  through  520 - 8  are suitable for coupling to a network, such as a coaxial feed network. 
       FIGS. 6 -A and  6 -B are an illustrative diagram of one embodiment of a dual-feed network  620  in  FIG. 6 -A, and a circuit  630  in  FIG. 6 -B. Dual-feed network  620  includes feeder PCB  622 , feeder PCB  624 , feeder PCB  626 , and feeder PCB  628 . Each of the four feeder PCBs is configured to engage two radiating elements via feed ports in the antenna elements, such as feed ports  220 - 1  through  220 - 8  in  FIGS. 2, 3, and 4 . The four feeder PCBs, when attached to the radiating elements, dictate the spacing between neighboring elements. For example, feeder PCB  622  includes a notch  636  at the top edge where it would engage the radiating elements. The dimensions of notch  636  are a function of the wavelength and target impedance of the radiating elements. In the embodiment of  FIGS. 6 -A and  6 -B, the notch width is λ/32. The boundaries of notch  636  are conductive and effectively form a parallel-plate capacitor. Each of the four feeder PCBs also includes a conductive trace  638  that couples the two engaged radiating elements. Together, notch  636  and conductive trace  638  can be represented as an LC circuit. The size and shape of notch  636  and conductive trace  638  are designed such that the representative LC circuit has an impedance that matches the target impedance for the radiating elements. 
     Circuit  630  includes two cross polarized dipole feed circuits, dipole feed circuit  632  and dipole feed circuit  634 . When coupled to dual-feed network  620 , dipole feed circuit  632  is coupled to feeder PCB  624  and feeder PCB  628 , and dipole feed circuit  634  is coupled to feeder PCB  622  and feeder PCB  626 . 
       FIG. 7  is an illustrative diagram of one embodiment of a dual-feed dual-polarized UWB antenna  700 . Antenna  700  includes a cylindrical housing  710  that contains an assembly of circuit  630  and dual-feed network  620  of  FIGS. 6 -A and  6 -B, and a UWB antenna element  720 . Cylindrical housing  710  can be conductive, providing cross-polarization isolation and −3 dB beamwidth stability over the operating frequency band. As an example, the housing comprises metal-plated cast-plastic. The amount of isolation is adjustable according to the height of cylindrical house  710 . UWB antenna element  720  is dual-polarized and is dual-feed, as are the embodiment antenna elements of  FIGS. 2, 3, 4, and 5 . UWB antenna element  720  includes four shared-element dipole antenna elements, each having two circular radiating elements, similar to antenna element  200  of  FIG. 2 . Dual-feed network  620  is coupled to UWB antenna element  720  via the eight feed ports respectively disposed on the four radiating elements. Dual-feed network  620  is also coupled to circuit  630 , thereby coupling dipole feed circuit  632  to feeder PCB  624  and feeder PCB  628  of  FIGS. 6 -A and  6 -B, and coupling dipole feed circuit  634  to feeder PCB  622  and feeder PCB  626  also of  FIGS. 6 -A and  6 -B. 
     The embodiment of  FIG. 7  illustrates UWB antenna element  720  as that of antenna element  200  of  FIG. 2 . Referring to the embodiment of  FIG. 2 , through dual-feed network  620 , dipole feed circuit  632  is operable to feed shared-element dipole antenna element  630 - 2  and shared-element dipole antenna element  630 - 4 . Likewise, dipole feeder circuit  634  is operable to feed shared-element dipole antenna element  630 - 1  and shared-element dipole antenna element  630 - 3 . 
       FIG. 8  is an illustrative diagram of another embodiment of a feed circuit  800 . Feed circuit  800  includes a first dipole feed circuit  810  and a second dipole feed circuit  820 . Each of the two dipole feed circuits includes a main branch that splits into two smaller branches. The two smaller branches are opposingly disposed on feed circuit  800 . First dipole feed circuit  810  and second dipole feed circuit  820  are orthogonal with respect to each other. As in the embodiment of  FIG. 6 -B, feed circuit  800  is configured to be couplable to a feed network for feeding at least four antenna elements. 
       FIG. 9  is an illustrative diagram of another embodiment of a dual-feed dual-polarized UWB antenna  900 . UWB antenna  900  includes feed circuit  800  of  FIG. 8  and further includes an element structure  910 , a feed structure  920 , dielectric layer  930 , and a coaxial feed network  940 . Element structure  910  includes four radiating elements similar to those in the embodiments of  FIGS. 2, 3, 4, and 5 . In the embodiment of  FIG. 9 , element structure  910  is formed of a cast conductive material, such as aluminum. Element structure  910  is cast along with feed structure  920  as a single conductive component. Coaxial feed network  940  is disposed within feed structure  920  and couples element structure  910  to feed circuit  800 . Coaxial feed network  940  is a dual-feed network that couples neighboring radiating elements of element structure  910 , thereby forming four shared-element dipole antenna elements. The shared-element dipole antenna elements are fed by coaxial feed network  940  through feed structure  920 , which couples each radiating element to feed circuit  800 . 
     Beneath element structure  910  is dielectric layer  930 . The shape and dimensions of element structure  910  are functions of the wavelength of UWB antenna  900 , and are therefore functions of the effective dielectric constant of element structure  910 . The addition of dielectric layer  930  beneath element structure  910  effectively increases the dielectric constant of element structure  910 , yielding a smaller wavelength and more compact radiating elements. Feed structure  920  is designed to achieve the target impedance for the radiating elements by providing a λ/32 spacing between neighboring elements. Additionally, the vertical portions of feed structure  920  form parallel plate capacitors, similar to those in feed network  620  in  FIG. 6 -A, and coaxial feed network  940  creates an inductance. The impedance of each of the four radiating elements can be represented by the corresponding LC circuit. 
       FIG. 10  is another illustrative diagram of the dual-feed dual-polarized UWB antenna  900  of  FIG. 9 . UWB antenna  900  includes cylindrical housing  1010 , which is similar to cylindrical housing  710  of  FIG. 7 . Cylindrical housing  1010  contains UWB antenna  900  of  FIG. 9 , which further includes feed circuit  800 , feed structure  920 , element structure  910 , and dielectric layer  930  attached beneath element structure  910 . 
       FIG. 11  is a flow diagram of one embodiment of a method for manufacturing a dual-feed dual-polarization antenna element. The method begins at a start step  1110 . At a first forming step  1120 , four radiating elements are formed. The four radiating elements are arranged in a co-planar diamond pattern. Neighboring elements of the four radiating elements form four shared-element dipole antenna elements. Each of the four radiating elements is shared between two cross-polarized dipole antenna elements of the four shared-element dipole antenna elements. In certain embodiments, the four radiating elements are disposed on a PCB. The four radiating elements may be formed in copper, or other material, over a dielectric substrate. Forming the elements over the dielectric substrate can be done by a variety of PCB processes, including both additive and subtractive techniques. In other embodiments, the four radiating elements are composed of cast aluminum. Cast aluminum radiating elements can also include a cast aluminum feed network, the elements and feed network being formed in a single cast aluminum component. Additionally, in some embodiments, the cast aluminum radiating elements have a dielectric layer attached on the underside of each of the elements. The dielectric layer, for a given operating frequency band, allows more compact antenna elements via a reduced wavelength due to the modified effective dielectric constant. 
     At a second forming step  1130 , eight feed ports are formed. The eight feed ports are arranged in four cross-polarized dual-feed pairs. The pairs are respectively disposed on the four radiating elements. Each feed port of the four cross-polarized dual-feed pairs is operable to respectively excite one of the four radiating elements for a cross-polarized one of the four shared-element dipole antenna elements. The size and locations of the feed ports on each of the radiating elements are determined according to the wavelength and the target impedance. Additionally, the type of feed network to which the dual-feed dual-polarization antenna element is couplable dictates the shape of the feed ports. For example, in embodiments for use with a coaxial feed network, the feed ports should be circular. In embodiments for use with a PCB feed network, the feed ports are typically rectangular slots. Feed ports can be formed on the radiating elements by removing the conductive and any dielectric material that may be present at the feed port site. For example, in embodiments where the radiating elements are formed on a PCB, the feed ports are formed by cutting or drilling through the copper and substrate, leaving an opening through which a PCB feed network can couple, or through which a coaxial feed network can couple. In embodiments having cast aluminum radiating elements, the feed ports are specified in the cast and are formed concurrently with the radiating elements. In embodiments having a single component cast aluminum feed network and radiating elements, the radiating elements, feed network, and ports are all cast concurrently. The method then ends at an end step  1140 . 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. For example, instead of having four radiating members, it is possible to have any multiple of four (eight, twelve, sixteen, twenty, for example) arranged in substantially a similar way as the four members radiating illustrated herein. It is therefore intended that the appended claims encompass any such modifications or embodiments.