Passive microwave direction finding with monobit fourier transformation receiver and matrix coupled antenna

Abstract

A passive instantaneous microwave signal frequency identifying and angle of arrival identifying system employing a beam steering multiple element antenna coupled through a Butler matrix to a plurality of simplified Fourier transformation radio receivers wherein unit value or near unit value magnitudes of the Kernel function ##EQU1## in the receivers' Fourier transformations are used to elude transformation computation complexity and resulting radio receiver size and cost penalties. Limiting amplifiers, a video signal path and direction finding encoding logic are also employed. Airborne military application of the system in electronic warfare direction finding, radar frequency determination and other activities is included.

Description

BACKGROUND OF THE INVENTIONWhen a military aircraft flying in unknown or hostile air space is discovered by a distant radar apparatus it is often beneficial for the crew of the aircraft to not only be made aware of the occurrence of this radar discovery but to also be appraised of as much information regarding the discovering radar as is possible. Two significant portions of this discovering radar information are the physical location of and the operating frequency of the distant radar apparatus. In addition to the fundamental act of receiving such information concerning the discovering radar apparatus it is desirable that this information become available to the aircraft crew as quickly as is possible and that the information be obtained from as little as one pulse of energy received from a threat signal source. The obtaining of this and other information such as pulse duration and signal strength data in a passive non-signal radiating manner from a distant threat signal is the rol...

AI Technical Summary

Benefits of technology

The present invention provides a simplified, small size, passive, instantaneous- opera

Problems solved by technology

Although radio receivers technically capable of performing in this direction finding and frequency identification environment have existed for some time the cost, technical complexity and physical size of each such existing receivers and related problems such as relatively short intervals of mean time between receiver failure events have limited the practicality of direction finding apparatus using existing electronic warfare receivers.

This limitation is especially notable with respect to locating such apparatus within the confines of and within the weight limitations of a host aircraft such as a tactical or fighter aircraft.

When the cost, technical complexity and physical size associated with each of these previous receiver types is considered, the limited utility of the resulting Cohen FIG. 1 system, particularly in a small aircraft, begins to emerge however.

A significant part of the difficulty with the previous digital FFT receivers heretofore potentially used in monopulse frequency and direction-finding applications relates to the algorithm used to embody the Fourier transformation operation in the receiver.

Both the number of and the size of each individual of these multiplications contributes to the complexity of rigorously implementing the Fourier transformation in either hardware or software form and especially to the difficulty of implementing this operation in real time.

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