Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
1997-06-23
2001-02-06
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S770000, C343S912000
Reexamination Certificate
active
06184839
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to antenna systems and, more particularly, to flat, relatively thin broadband reflectors capable of receiving and transmitting radio frequency waves, particularly in the microwave range.
BACKGROUND OF THE INVENTION
An antenna is a conductor or system of conductors designed to radiate or intercept electromagnetic waves. While being varied in size and shape, all antennas are made up of conducting material and require a feed system to extract or accept energy. An antenna converts guided electric waves into electromagnetic waves in free space. A matching device of some sort is generally employed to facilitate this conversion, and a transmission line is often used to efficiently guide the electric waves from the transmitter to the antenna.
Antennas employing parabolic reflectors have been in widespread use for many years to direct the wave front to the receiver in phase. This is accomplished by the geometry of the parabolic reflector which provides a constant path length from any point on the reference plane to the receiver. Basically, waves arriving at the reflector surface in phase are reflected to the focal point along equi-distant paths, thereby arriving at the focal point in phase.
Because of the resulting high gain, the constant path length parabolic antenna is popular for use at many wavelengths, including microwave and visible. For a satellite receiving station, the diameter of the parabola is a function of the merit factor, G/T, linking the gain G of the parabola and the overall noise temperature (T) desired on the station. Generally, the diameter of the parabola defines its beam width. At the same time, the beam width determines the sensitivity of the system to interference coming from satellites adjacent to the satellite aimed at, which limits the ability to reduce the diameter of the parabola.
The packaging, deployment, size and pointing difficulties for employing a conventional parabola make it impractical for use in space as well as in other applications.
Flat array antennas are being used to overcome the limits imposed by parabolic designs. In an array antenna, an array of receiving elements are arranged in parallel, and the gain is a function of the area of the antenna. However, for flat array antennas employing summing systems, efficiency decreases as area increases because of the loss generated in the summing systems.
An example of a flat array antenna having a summing system is described in U.S. Pat. No. 5,227,808 to Davis. The antenna array is constructed in sub-arrays which are supported in a stacked and folded condition and then expanded when deployed in space. Each sub-array includes a plurality of tapered notch antenna elements, each of which is fed by a section of slotline, which is in turn fed by a coplanar waveguide.
While electronic phasing devices used in conjunction with flat array antennas might be generally workable, they tend to be complicated, fragile and difficult to assemble.
A need exists for antennas having in excess of 10% bandwidth for high quality data transmission, which are light weight for ease of rapid pointing and are capable of high gain, while at the same time being physically thin for ease of storage and deployment and low blockage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a reflector array for an antenna in which the low loss and large bandwidth are simultaneously achieved.
Another object of the present invention is to provide a reflector array in which operation and collimating of the radio frequency (RF) energy is achieved by the phasing of the RF energy that is re-radiated by each aperture of the array when the entire reflector surface is illuminated by the feed line.
Another object of the present invention is to provide a time delay in the elements of the array so that reflected, or transmitted, waves are in phase without the need for electronic summing devices or other electronic means.
Another object of the present invention is to provide a reflector array which is relatively simple in construction and cost effective to produce.
Still another object of the invention is to provide a reflector array which can be folded and stowed in a compact state for subsequent deployment with relative ease in an expanded state.
Yet another object of the invention is to provide very high antenna gain and large frequency bandwidth, such as greater than 45 db gain, in the physically thinnest structure possible that does not exceed, for example, two and one half inches.
These and other objects are met by providing a reflector for an antenna which includes a plurality of reflector elements, each having a transmission line and an aperture at a distal end of the transmission line, each transmission line having a length which varies in accordance with the position of each aperture relative to the antenna.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.
REFERENCES:
patent: 2960693 (1960-11-01), Fry
patent: 4684952 (1987-08-01), Munson et al.
patent: 4862190 (1989-08-01), Palmer et al.
patent: 5227808 (1993-07-01), David
patent: 5268701 (1993-12-01), Smith
patent: 5309165 (1994-05-01), Segal et al.
patent: 5359338 (1994-10-01), Hatcher, Jr. et al.
Butscher Frank D.
Dawley William J.
Loane Joseph T.
Tanner David R.
Lockheed Martin Missiles & Space Company
Swidler Berlin Shereff & Friedman, LLP
Wimer Michael C.
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