Patent Grant
9843108
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.
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.
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.
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:
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,
where, C is the speed of light, fcenter 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.
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
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
Continuing the embodiment of
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
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.
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.
The embodiment of
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
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.
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.
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