The present invention pertains generally to antenna systems that have possibly omni-directional radiating elements. More specifically, the present invention pertains to antenna systems and methods for manufacture there for that allow for beam steering and nulling of an antenna having a single or multiple elements by modifying the structure of the antenna radome, which allows for beam steering and nulling using minimal antenna element transmission resources.
There are many transceivers in the prior having single-element antennas, such as GPS devices, for example. GPS devices can often include single-element antenna elements because of cost and size constraints. Other platforms which can include single-element antennas can include UUV's and UAV's and small maritime platforms. These types of platforms have extremely constrained antenna footprints, and space for these antennas is at a premium. The resulting received signals from such GPS devices and such platforms can be extremely weak and corrupted by interference. The resulting transmitted signals from such platforms may be weak in desired directions. One way to “boost” the reception power of such devices is to employ phased array antennas that have multiple receiving/radiating elements, such as Controlled Reception Pattern Antennas (CRPA). But these types of systems can often require more space than that allotted for the platform. Additionally, the control requirements, costs, and electronics to drive the multiple elements for such antennas can be unduly burdensome to the platform. On the other hand, legacy systems employing a single-element antenna such as a Fixed Reception Pattern Antenna (FRPA) antenna are susceptible to interference.
As mentioned above, beam steering can be generally accomplished with multiple element phased-arrays. Recently, there has been some interest in making active (or beam-steering) radomes using metamaterials. Such radomes take advantage of the phenomena caused by wave interaction due to passing the RF through a thick radome made of metamaterials. However, these techniques can place a strong dependency on the radome material, which imposes certain requirements such as attenuation, frequency response, weight and size. With regard to weight and size in particular, the use of metamaterials for active radome beam steering may be a huge disadvantage for a small airborne platforms such as UAV's.
In view of the above, it is an object of the present invention to provide an active radome that allows for beam steering and nulling, with potentially multiple beams or nulls, with a single element for radiating or receiving radiofrequency (RF) energy, which results in a more agile single-element GPS antenna or other receiving or transmitting antenna. Another object of the present invention is to provide an active radome with the employed switched conducting elements, such that a thick slab for the radome is not required, while still achieving the desired wave changes (beam steering/nulling). Still another object of the present invention is to provide an active radome with conductive switching elements rather than metamaterials, which may result in an improved frequency response for the overall antenna, while significantly reducing the radome attenuation, weight and size properties, which are of great concern on mobile platforms. Another object of the present invention is to provide an active radome that mitigates interference affecting an existing antenna by effectively using minimal resources and without the need to replace the antenna. Still another object of the present invention is to provide a radome for a single-element antenna that provides directionality for that antenna within a confined space. Yet another object of the present invention is to provide an active radome that can be adapted to be back-fit over an existing antenna, along with circuitry that adaptively controls the various elements in the radome. Another object of the present invention is to provide an active radome that is easy to manufacture in a cost-effective manner.
An antenna in accordance with several embodiments of the present invention can include at least one omni-directional element for radiating or receiving radiofrequency (RF) energy and an active radome surrounding the radiating element, with the radome having an internal and an external surface. A plurality of conductive segments can be placed between the radome and the element, or on the inside surface of the radome. A plurality of switches can interconnect the conductive segments to form a network of conductive segments that surrounds the radiating element.
The switches can be MOSFET, JFET, relay, or optical switches, or switches of other types, and the switches can be selectively activated in real time when the element radiates or receives RF energy to establish connectivity between the conductive segments as selected by the user, to thereby establish an effect similar to the“Yagi” effect, thus producing the desired directionality for the antenna. The conductive segments network can surround the element and can have an octagonal, square, polygonal of other order, or circular profile when viewed in top plan. Other geometric profiles are also possible, as long as the conductive segments enclose or surrounding the radiating element. The conductive segments network can also be fixed to the radome and conform to the shape of the radome. The antenna can further include a processor, which can contain non-transitory written directions that selectively activate and deactivate the switches to establish the Yagi-like effect for the possible omni-directional element or elements. The radome can further be manufactured from an RF energy transparent material, or contain metamaterial with customized electric permittivities and/or magnetic permeabilities in various places to enhance the aforementioned directional effect of the antenna.
The novel features of the present invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similarly-referenced characters refer to similarly-referenced parts, and in which:
Referring initially to
Conductive segments 16 and switches 18 can cooperate to define a network 19 for antenna 10. As shown in
In
Referring now to
The geometry of the network 19 can be circular, square or octagonal, or any other shape when viewed in a plan view, according to needs of the user and the results of the computational step 105, as also described above. Finally, the switches can be selectively opened and closed according to a predetermined algorithm (not shown), as indicated by step 110 in
The switches 18 can be connected to the processor 20 with optical fibers or with wires. When wires are used, the wires can have a high resistivity, which is sufficiently high to minimize the effect of the wires on the electromagnetic field patterns and hence on the directionality performance of the antenna 10. In other embodiments, the switches can be controlled by electric or magnetic or RF or optical signals, which can be sent to the switches wirelessly (without wires or optical fibers connected to network 19), and can operate in a manner similar to RFID (Radio Frequency Identification) technology, i.e. by using RFID tags. Or, in a manner similar to RFID, each switch can have a built-in electronic address for use by the control signals, can harvest energy from the control signal energy, and can open or close in response to control signal commands that are directed to it by means of its own address.
Referring now to
In still other embodiments of the antenna 10, multiple networks 19 and optionally radomes 14 can be used to enhance the directionality effect of the device. For these embodiments the multiple network 19 and/or radomes 14 can be arranged concentric to each other, with each radome 14 and network 19 having a surrounding relationship with radiating element 12. Or, if directionality in a particular direction or directions is desired, and the desired of direction(s) will not change, the networks and radomes can be placed to enhance the reflector element and director element function of the Yagi effect in a specific direction or directions when the corresponding switches 18 are closed as described above. Additionally, the radome 14 can be made of metamaterials, either uniformly or in specific portions of the radome 14, in order to further enhance the directionality of the antenna. Metamaterials with electric permittivity and/or magnetic permeability could be used (for purposes of this disclosure a metamaterial is a material whose electric permittivity and/or magnetic permeability has been designed, typically by embedding microscopic or small elements into the radome material to meet desired criteria). Materials that could be used for the conductive segments 16 and 18 are described above, although other materials could be used.
A prior art Yagi antenna achieves directionality by means of one or more reflector elements and one or more director elements. For the present invention according to several embodiments, an antenna 10, or an antenna having an active radome 14, can have elements that function in a similar manner to the reflector and director elements of a Yagi antenna. An active radome can have elements that do not function as reflector or director elements. An active radome can function in a manner similar to a Yagi antenna, and the resemblance has been noted herein. However, in some embodiments an active radome can function differently from a Yagi antenna.
The use of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This invention (Navy Case No. 101154) is assigned to the United States Government and is available for licensing for commercial purposes. Licensing and technical inquires may be directed to the Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif. 92152; voice (619) 553-5118; email ssc_pac_T2@navy.mil.
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