Hughes Aircraft Company

Hughes Electronics Corporation

Henry L McCord

David A Whelan

A passive imaging system that uses an antenna having two antenna elements. The system cross-correlates received signals with a reference function to achieve high resolution. The antenna elements are rectangular with their long dimensions oriented normal to the longitudinal axis of a carrying vehicle and the elements are separated by a distance consistent with image resolution requirements. Additionally, the antenna elements are frequency scanned in the cross-track dimension. The channel for the forward antenna element has a time delay relative to that of the rear antenna element. This time delay achieves pointing of the antenna at a particular forward angle relative to the normal to the velocity vector. Outputs of IF filters of the antenna elements are synchronously detected to provide in-phase and quadrature (I/Q) components of their phase modulated product. These I/Q components are processed by an analog-to-digital converter and digitally filtered to select a phase modulation frequency band about the chosen forward angle. The real pan of the output of the digital filter is stored and is the cross-track channel signal is cross-correlated with the reference function. The output of this cross-correlation provides high along-track resolution with suppressed along-track sidelobe responses. The reference function is a weighted, limited-extent, replica of the real pan of the phase of a small-area signal as such signal passes through the forward angle. The reference function weighting suppresses correlation function sidelobes and is adjusted to include a component introduced by the bandwidths of the IF receivers, the angle extent that is used, and the separation between the antenna elements. A separate set of processing circuits is provided in parallel for each cross-track image channel at the output of the intermediate frequency (IF) amplifiers of both antenna elements. A fixed bandwidth is provided in each cross-track image channel, but the center frequency is different in order to point the beams of the antenna elements at a chosen cross-track position.

Correlation radiometer imaging system

A synthetic array processing system which simultaneously develops a plurality of parallel synthetic beams, each beam being spaced in time along a flight path and having different effective phase centers. Means are provided for storing and reading out a plurality of doppler history signals from each of a plurality of range positions and in one embodiment of the subject invention the read out sweep lengths are programmed as a function of the square root of range to allow use of a constant slope focusing oscillator. The center frequency of the doppler histories are offset as a predetermined function of range and applied through a focusing mixer to a time compression filter circuit. A plurality of compressed pulses provided at the output terminal of the compression filter circuit, each represent a doppler history of a point reflector and a synthetic beam and these signals are applied to a display which may be controlled as a function of the square root of range.

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Los Angeles, CA, United States of America

Henry L McCord