Patent Application
20140009346
The system and techniques described herein relate generally to radio frequency (RF) antennas, more particularly, to scanned RF antennas.
As is known in the art, there is a trend to increase the number of radio frequency (RF) antennas disposed on both commercial and military structures including both airborne and land-based structures and vehicles. Such structures and vehicles may be either stationary or mobile. For example, RF antennas are often disposed on cell towers, missiles, aircraft, and mobile ground based vehicles.
As is also known, there is an increasing trend to place even more RF antennas on such structures. Since there is often a limited amount of space in which to place the antennas, there is a concomittant increase in the value of the space occupied by each antenna. Accordingly, it is desirable to utilize RF antennas which occupy the least amount of space (i.e. occupy the least amount of volume and real estate on the structures) while still providing a desired level of performance. Utilizing compact RF antennas frees up valuable surface area and in structures on which the RF antennas are disposed.
In missile applications, for example, high gain fixed beam antennas (e.g. fuse antennas) typically occupy a relatively large volume in order to provide the antenna having desired gain and antenna pattern characteristics. It would, therefore, be desirable to provide compact antennas which occupy a relatively small volume compared with conventional antennas providing the same function. For example, it would be desirable to provide compact fuse antennas which occupy a relatively small volume compared with conventional fuse antennas having substantially the same desired gain and antenna pattern characteristics.
In accordance with the concepts, systems, circuits and techniques described herein, an antenna includes a single element radiator having a frequency selective surface (FSS) disposed over a first surface thereof and a Fresnel surface disposed over a second opposing surface of the single element radiator.
With this particular arrangement, a compact antenna having a volume which is relatively small compared with similarly functioning conventional antennas is provided. The combination of the single radiator and the FSS provides the antenna having a gain characteristic which is increased over antennas which occupy the same amount of space. Furthermore, the Fresnel surface acts as a reflecting surface which provides beam shaping and scanning. Making use of frequency selective surfaces and reflective ground planes provides the antenna having enhanced gain and scan characteristics while maintaining a relatively small volume. Furthermore, by utilizing a single element radiator and making use of an FSS, a highly efficient, compact radiating conformal antenna is provided.
Benefits of providing an antenna from a single radiator and a frequency selective surface (FSS) include, but are not limited to: simpler construction, reduced antenna volume which frees up volume on the structure on which the antenna is mounted, an enterprise wide solution (i.e. this antenna approach can be used in a wide variety of different applications); reduced costs (due to both ease of construction and commonality of design across a wide number of different applications). Furthermore, the antenna described herein is less complex than other antennas having similar gain and scanning characteristics which results in antennas having a reliability characteristic which is higher than the reliability characteristic of functionally similar antennas.
Referring now to
Antenna 12 includes a single element radiator 14 (
In on embodiment, FSS 16 is provided from a dielectric substrate having conductors patterned or otherwise provided on one or both surfaces thereof. The FSS can be designed in the conventional sense, however, a quarter wavelength thick dielectric substrate may also be used for the reflective surface.
Antenna 12 further includes a Fresnel zone reflecting surface 18 (also sometimes referred to herein as Fresnel reflector 18) disposed about the second surface of single element radiator 14. Fresnel reflector 18 provides antenna 12 having a beam steering function. The Fresnel reflector rings 18 are designed such that the rays of radiation coming from the FSS reflect off the Fresnel zones patterns resulting in collimation at a desired scan angle. In the exemplary embodiment of
Single radiator 14 makes use of both FSS 16 top surface and Fresnel zone reflecting ground portion 18 for beam steering in order to achieve a high gain small aperture scanned radiation.
Referring now to
As shown in
Referring now to
Referring now to
Each antenna element 42a-42c produces a fan beam radiation pattern shape. That is, the main beam is pointed off angle from the forward direction (as designated by reference numeral 44), with partial pattern coverage in the circumferential direction. A frequency selective surface 46 is provided from a plurality, here four, conductive elements 48a-48d. It should be appreciated that the number of rings 48 are selected in accordance with the needs of a particular application. It should also be appreciated that the rings could also be provided as discrete length dipoles. The widths of the rings will determine the amount of reflectivity and therefore enhanced gain from that of a single radiator. It should also be appreciated that the rings (or bonds) need not be continuous. For example, the antenna would still operate as desired if the bands passed across the single antenna element and then stopped. For example, the bands or rings may be provided from a series or segments of conductors (e.g. as in a “dashed” or “dotted” line depending upon the length of each segment). It should be appreciated that since the FSS and Fresnel surface are in the near field of the antenna radiator, some coupling effects may occur and have to be addressed either through commercial three-dimensional modeling or solving the resultant boundary value problem analytically.
Disposed about each antenna element 42a-42c are a Fresnel surface provided by a plurality here two, Fresnel rings 50a, 50b. The number of bands or rings 50a, 50b are selected based, in part, upon the amount of gain enhancement desired and frequency bandwidth, the higher the gain enhancement the lower the frequency bandwidth of operation. It should be noted that bands 48 need not be continuous.
It should be appreciated that while the thickness of the FSS is not important, the thickness of the core material onto which the Fresnel pattern is etched should be about one-quarter wavelength. In one exemplary design, the single element radiator may be provided as one-half wavelength element, the spacing between the FSS and Fresnel patterns is also one-half wavelength. The FSS rings and spacing depends again upon the gain enhancement desired and BW trade.
Referring now to
Having described preferred embodiments which serve to illustrate various concepts, structures and techniques which are the subject of this patent, it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that that scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.
