Communications: radio wave antennas – Antennas – Logarithmically periodic
Reexamination Certificate
1999-11-29
2001-09-25
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Logarithmically periodic
C343S797000, C343S799000
Reexamination Certificate
active
06295035
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to antennas and more particularly to a circular direction finding antenna.
BACKGROUND OF THE INVENTION
A generic Direction Finding (DF) system consists of four major components: the antenna system, the receiver, one or more processors and the control/output system. The antenna system must address the contradictory requirements of both an omnidirectional pattern that permits reception over the widest possible field of view, and a “pencil beam” that permits great accuracy in determining the angle of arrival of an intercepted signal. These conflicting requirements cannot be met with a single static antenna. Resort, therefore, is often made to the use of an antenna array, a spinning narrow-band pattern antenna, or a phased array (an antenna capable of rapidly altering its radiation pattern by electronic means). One major problem with the spinner type of DF antenna is that once it locks onto a target, it is blind to the rest of the field of view. Phased array antennas have the disadvantage of requiring an assortment of expensive electronics to conduct the electronic beam scanning.
The fundamental trade-off between instantaneous field of view and time available for an observation is a design consideration of any DF system. Even an antenna with a modest field of view can be used to provide 360 degree coverage in a direction finder by rotating the antenna. However, rotating the antenna poses problems when dealing with frequency-agile emission or signals of short duration. The mean time required to intercept a signal and the duration of the signal being sampled critically depend upon the coincidence of the transmitting antenna pattern, which may also be turning, and the rotating DF antenna. It is such trade-offs that make the design of an effective DF system a challenge.
Previous attempts at designing such an antenna have all had various problems such as low gain, limited operational bandwidth, excessive size and weight, low angle of arrival (AOA) accuracy, and limited azimuthal field of view once a target is acquired. Some previous antenna designs have used low-gain dipole or spiral antenna elements. These designs offer simultaneous field of view coverage, but suffer from limited bandwidth and low AOA accuracy. Other antenna designs have larger bandwidths, but do not offer simultaneous coverage over the entire field of view.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a high accuracy, high gain, simultaneous track and scan, circular direction finding antenna. The present invention provides a circular direction finding antenna that addresses shortcomings of prior systems.
In accordance with one aspect of the present invention, an antenna system is provided that includes a plurality of mounting plates arranged in a generally circular configuration. Each mounting plate has an inside surface and an outside surface. Each antenna element has a high frequency end and a low frequency end. The low frequency end of each antenna element is mounted to the inside surface of one of the mounting plates such that the high frequency ends of opposed antenna elements face each other. The high frequency ends of opposed antennas are separated by one wavelength of the signal frequency received at the high frequency end. The antenna system also includes a beamforming network having a plurality of input ports equal to the number of antenna elements. Each antenna element is coupled to the beamforming network through a respective input port.
In accordance with another aspect of the present invention, an antenna system is provided that includes a generally circular array of a plurality of antenna elements. The plurality of antenna elements are divided into a plurality of groups. The antenna system also includes a plurality of beamforming networks. Each beamforming network is connected to one antenna element group such that the plurality of antenna elements are interleaved with one another.
Antennas incorporating the present invention provide numerous technical advantages. For example, one embodiment of the invention has exhibited angle of arrival accuracy of 0.5 degrees over a 0.5 to 18 GHz frequency range and a full 360 degrees field of view. This embodiment incorporates elements that are dual polarized, high gain, and light weight as compared to low gain spiral or dipole antenna elements. In addition, the use of certain coaxial cavity antenna elements can extend the frequency range to 0.5 to 40 GHz.
Another technical advantage of the present invention is continuous track and scan DF capability over a field of view of 360 degrees in azimuth and a minimum of ±40 degrees in elevation. The present invention minimizes the problem of blindness once a target has been located. In addition, an antenna in accordance with the present invention has few parts, and is simple to assemble and implement. The capabilities of an antenna in accordance with the present invention are obtained in a small size that is light weight and low cost. Yet another technical advantage of the present invention is an antenna that has a dual use as a polarimeter in the same aperture used for DF capabilities.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.
REFERENCES:
patent: 3731316 (1973-05-01), Sheleg
patent: 4101901 (1978-07-01), Kommrusch
patent: 4594595 (1986-06-01), Struckman
patent: 4962383 (1990-10-01), Tresselt
patent: 5021796 (1991-06-01), Corzine et al.
patent: 5164738 (1992-11-01), Walter et al.
patent: 5276457 (1994-01-01), Agarwal et al.
patent: 5506592 (1996-04-01), MacDonald et al.
patent: 5936588 (1999-08-01), Rao et al.
PCT Written Opinion dated Oct. 19, 2000 for PCT/US99/28127 filed Nov. 30, 1999.
Baker & Botts L.L.P.
Nguyen Hoang
Raytheon Company
Wong Don
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