Patent Application
20130028298
Typical microwave and millimeter-wave frequency directive antennas generally comprise cumbersome structures such as waveguides, dish antennas, helical coils, horns, and other large non-conformal structures. Communication applications where at least one communicator is moving as well as radar applications generally require a steerable beam and/or steerable reception. Phased array antennas are particularly useful for beam-steered applications since beam-steering can be accomplished electronically without physical motion of the antenna. Such electronic beam steering can be faster and more accurate and reliable than gimbaled/motor-driven mechanical antenna steering. Phased array antennas also provide a capability to have multiple simultaneous signal beams.
In addition, communications in multiple bands typically require either multiple antenna apertures for each of the bands and/or dual band dish antennas. On-aircraft dishes are generally placed under radomes, adding significantly to the weight of the aircraft, aerodynamic drag, and maintenance complication. A single wide-band phased array aperture minimizes vehicle integration cost and size, weight, and power needs compared to multiple single-band solutions and/or dish antennas. However, conventional low-profile designs using slot rings and/or microstrip patch antennas suffer from mutual coupling that limit their frequency coverage, scan volume, and axial ratio performance.
It is with respect to these and other considerations that the disclosure made herein is presented.
It should be appreciated that this Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to be used to limit the scope of the claimed subject matter.
A wide-band linked-ring antenna element is described herein for implementing a single, conformal phased array for satellite communications (“SATCOM”) that covers both the 17.7-20.2 GHz commercial and 20.2-21.2 GHz military SATCOM receive K-bands. An array of the antenna elements provides a wide scan volume better than 60 degrees of conical scan volume from boresight and maintains good circular polarization axial ratio over the specified frequency bands, while being very thin and lightweight. The antenna element may also be scaled to other frequency bands, used as a transmitting element, and used for other phased array antenna applications, such as line-of-sight communication links, signal intelligent (“SIGINT”) arrays, radars, sensor arrays, and the like.
According to one aspect, an antenna element comprises a linked-ring conductive resonator that is electromagnetically coupled to at least one feed line. The conductive resonator and feed line are further surrounded by a Faraday cage that is conductively coupled to an electromagnetically-shielding ground plane and operable to shield the conductive resonator and the feed line.
The features, functions, and advantages discussed herein can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
The following detailed description is directed to a wide-band, linked-ring antenna element for phased arrays. Utilizing the antenna element described herein, a single, conformal phased array may be implemented for SATCOM receive covering the adjacent military and commercial receive bands. The antenna element provides a wide scan volume better than 60 degrees of conical scan volume from boresight and maintains good circular polarization axial ratio over the specified frequency bands. The antenna element design is light weight and very thin. It also does not require a wide angle impedance matching (“WAIM”) layer or radome, thus greatly reducing aerodynamic drag of an aircraft as well as integration and maintenance costs. The antenna elements may also be scaled to other frequency bands and phased array antenna applications, used as transmitting elements, and used for other phased array applications, such as line-of-sight communication links, signal intelligence (“SIGINT”) arrays, radars, sensor arrays, and the like.
Embodiments of the disclosure are described herein in the context of a planar or conformal SATCOM phased array antenna. Embodiments of the disclosure, however, are not limited to such planar SATCOM applications, and the techniques described herein may also be utilized in other applications. For example, embodiments may be applicable to conformal antennas, manned and unmanned aircraft antennas, line-of-sight communications, sensor antennas, radar antennas, and the like.
In the following detailed description, references are made to the accompanying drawings that form a part hereof, and that show, by way of illustration, specific embodiments or examples. The drawings herein are not drawn to scale. Like numerals represent like elements throughout the several figures.
The conductive resonator 102 is implemented on the top, surface layer and is operable to resonate at electromagnetic frequencies to be received. According to embodiments, the conductive resonator comprises multiple ring elements that are linked by tuning tabs, as will be described in more detail below in regard to
The feed lines 104A, 104B (referred to herein generally as feed lines 104) are implemented on the second layer below the conductive resonator 102 and are electromagnetically coupled to the conductive resonator to drive the conductive resonator for transmit and/or receive a signal from the conductive resonator. According, to one embodiment, the feed lines 104A and 104B are implemented on the second layer using microstrip traces. It will be appreciated that the feed lines 104 may also be implemented using metallization, direct-write, and the like. The electromagnetic coupling may comprise inductive coupling, a capacitive coupling, and the like.
The Faraday cage 106 is operable to shield the conductive resonator 102 and the feed lines 104. The Faraday cage 106 comprises an electromagnetically-shielding ground plane 110 implemented on the lowest layer, a plurality of conductive vias 108 electromagnetically coupled to the ground plane 110 and rising through the layers of the multi-layer circuit board to the top layer, and a conductive strip implemented on each layer directly and electromagnetically coupling the vias 108 and the surrounding the conductive strips 106. The conductive strips may be implemented on the respective layers using metallization, microstrips, direct-write, and the like. According to one embodiment, the conductive vias 108 comprise holes drilled through the layers of the multi-layer circuit board and filled or plated with copper or other conductive material.
The conductive strips and conductive vias 108 may be arranged in a hexagonal shape surrounding the conductive resonator 102 and the feed lines 104, as shown in
The substrate or dielectric between the layers of the multi-layer circuit board may be constructed of a low-loss, low-dielectric-constant circuit board material, such as RT/DUROID® 5870/5880 boards from Rogers Corporation of Chandler, Ariz. It will be appreciated that the multi-layer circuit board may be constructed from any suitable low-loss low-dielectric-constant material. According to one embodiment, the thickness of the dielectric between the first two layers, labeled TL1, may be about 20 mils, and the thickness between the remaining layers, labeled TL2 and TL3, may be about 31 mils. Not shown in the figures are adhesive layers between layers 1, 2, and 3. It will be appreciated that the number of layers implemented, the method to adhere the layers together, and the thicknesses TL1, TL2, and TL3 of the dielectric between the layers in the antenna element 100 may be varied to provide the desired overall thickness of the conformal array, and to implement a Faraday cage 106 that is capable of minimizing coupling from adjacent antenna elements and allow the antenna element to scan down to 60 degrees or better from boresight. In addition, the number, size, and spacing of the conductive vias 108 in the Faraday cage 106 may also affect the performance of the cage and the antenna element. In one embodiment, the conductive vias 108 may have a radius of about 7 mils.
In a further embodiment, the inner radius RR1 of the inner ring element 302B may be about 36.6 mils, while the inner radius RR2 of the outer ring 302A may be about 53.6 mils. The thickness TR1 of the inner ring 302B may be about 6.2 mils and the thickness TR2 of the outer ring element 302A may be about 24.8 mils, with a clearance CLR1 between the rings of about 10.8 mils. Each tuning tab 304 may have an inner width W1 of about 22.2 mils and an outer width W2 of about 27.7 mils. This structure may allow the conductive resonator 102 of the antenna element 100 to perform optimally in the 17.7-21.2 GHz adjacent commercial and military SATCOM receive bands. It will be appreciated that the number of ring elements 302 and tuning tabs 304 and their corresponding dimensions RR1, RR2, TR1, R2, W1, W2, and CLR1 may be varied in order to tune the linked-ring conductive resonator 102 for suitable operation in the desired frequency bands.
Further shown in
The feed lines 104A and 104B may be connected to signal sources by coupling vias 402 that run from the bottom of the microstrip feed lines, through the remaining layers, layer 2 and layer 3, and to via pads (not shown) located in an aperture 404 in the ground plane 110 at the bottom layer, layer 4, of the antenna element 100. In a further embodiment, the feed lines 104A and 104B are located about 20 mils below the conductive resonator 102, and have a thickness TR3 of about 4 mils and a radius RR3 at the connection point to the coupling vias 402 of about 8 mils. The minimum separation MS between the opposite ends of the microstrip feed lines 104A and 104B may be about 12 mils. It will be appreciated that thickness TR3, board layer adhesion methods, radius RR3, the minimum separation MS, and the length and placement of the feed lines 104A and 104B may be varied to provide optimal operation of the antenna element 100 in the desired frequency bands.
The coupling vias 402 may be about 4 mils in radius and run about 62 mills through the remaining layers to the via pads in the ground plane 110. The via pads may be about 8 mils in radius, while the apertures 404 in the ground plane 110 for the via pads may have a radius of about 18.4 mils. The via pads may be further electrically coupled to communication electronics (also not shown) that provide independent signaling to and from the antenna element 100. Further shown in
Embodiments of the antenna element 100 described herein provide for the construction of single conformal phased passive array antenna with minimal size, weight, and power (“SWAP”), as well as minimal integration cost. The SWAP is greatly reduced by elimination of multiple narrow-band “stove-piped” SATCOM banded systems and associated separate antenna installations. Embodiments further provide a phased array antenna that can cover at least two SATCOM adjacent receive frequency bands, while being thin and lightweight. Embodiments can be scaled to other frequency bands and phased array antenna applications, such as line-of-sight communication links, SIGINT arrays, radars, sensor arrays, and the like.
It will be appreciated that the configuration and dimension of the various components, including the linked-ring conducting resonator 102, the microstrip feed lines 104, and the conductive strips 202 and conductive vias 108 that comprise the Faraday cage 106, shown in the figures and described herein represent exemplary implementations of the of the antenna element 100, and that other implementations will become apparent to one skilled in the art upon reading this disclosure. In addition, various components may be added, removed, or substituted, and various techniques may be used in the manufacturing of the antenna element 100 beyond those described herein. It is intended that this application include all such implementations of the antenna element 100 manufactured by any process or method known in the art.
Turning now to
From operation 502, the routine 500 proceeds to operation 504, where the feed lines 104 of the antenna element 100 are electrically coupled to communication electronics that provide independent signaling to and/or from the antenna element 100. As described above, the communication electronics may comprise special purpose electrical circuitry, software or firmware of general-purpose computing devices, any combination of these, and the like. In addition, the communication electronics may be partially or completely implemented on the multi-layer circuit board containing the antenna elements 100 of the phased array.
The routine 500 proceeds from operation 504 to operation 506, where the communication electronics detects a signal from one or more of the feed lines 104 coupled to the conductive resonator 102 to receive a signal in a first K-band. For example, the communication electronics may utilize the antenna element 100 to receive a signal in the 17.7-20.2 GHz commercial SATCOM receive K-band. According to one embodiment, the communication electronics may utilize two feed lines 104A and 104B implemented at substantially right angles to each other in the antenna element 100 to selectively receive a right-hand circular polarized or left-hand circular polarized signal (or dual orthogonal linear polarizations for other applications) through the conductive resonator 102.
From operation 506, the routine 500 proceeds to operation 508, where the communication electronics detects a signal from one or more of the feed lines 104 coupled to the conductive resonator 102 to receive a signal in a second K-band. For example, the communication electronics may utilize the antenna element 100 to receive a signal in the adjacent 20.2-21.2 GHz military SATCOM receive K-band. From operation 508, the routine 500 ends.
Based on the foregoing, it should be appreciated that technologies for a wide-band, linked-ring antenna element for phased arrays are provided herein. The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.
