Hughes Aircraft Company

Preben B Jensen

Robert W Klatt

Edward L Arnn

A chirped backscatter filter 10 compares a received signal (RSIG) to a reference signal related to a transmitted signal (TSIG) and removes from RSIG the frequency component which is equal to TSIG in frequency. This removed frequency component corresponds to the frequency of the transmitter backscatter radiation. The filter of the invention adds a frequency offset (f.sub.n) to both RSIG and TSIG in mixers 12 and 14 before substracting one from the other in mixer 22. Thus, equal frequency components in both RSIG and TSIG, such as the backscatter radiation frequency component of RSIG, will equal f.sub.n. The frequencies resulting from this subtraction are thereafter passed through a notch filter 24 which is centered on f.sub.n and which passes all frequency components except f.sub.n. The output of the notch filter thus no longer has a frequency component associated with the backscatter frequency component. The loss of the RSIG phase reference due to the phase reference between the RSIG and TSIG modulation envelopes being destroyed during the backscatter filtering process is therafter compensated for by adding TSIG to the filtered difference frequency component, thereby reestablishing the phase relationship of the original RSIG frequency components minus the backscatter frequency component.

Chirped backscatter filter

An enhanced quadrature notch filter which is capable of rejecting an undesired signal component of an input signal, generally comprising a quadrature phase splitter for producing first and second reference signals which have substantially the same frequency as the undesired signal component but which are 90.degree. out of phase with each other, a pair of amplitude control loops for adding the first and second reference signals to the input signal in amplitudes which will cancel the undesired signal component, and a phase locked loop circuit for maintaining a predetermined phase relationship between the undesired signal component and one of the first and second reference signals.

Enhanced quadrature notch filter

A system for generating a serial video signal from a plurality of parallel channels particularly useful in thermal imaging systems incorporating bi-directional scanning. Signals on parallel input lines are simultaneously sampled and held by individual sample and hold circuits in each channel. A first multiplex level having a plurality of slow multiplexers is arranged so that each slow multiplexer selects a subset of the total number of analog inputs to generate a serial output from each slow multiplexer. Each such single output is coupled to a high speed gate in a fast multiplexer to generate a serial output from a single output channel. The fast multiplexers operate at a rate determined by the output scan time divided by the number of parallel input channels. The slow multiplexers operate at a fraction of this speed where the fraction is equivalent to one over the number of slow multiplexers generating an input to the fast multiplexer.

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Rancho Palos Verdes, CA, United States of America

Preben B Jensen