Optical processing of radar signals with fresnel diffraction masks.

A simple real-time coherent optical processor is investigated. The processor uses a filter mask upon which is recorded the Fresnel field of the signal replica. Target range-Doppler information is obtained by observing the time and position of the output. A distinguishing feature of the processor is that for the ordinary PCW pulse, these output quantities are correlated, albeit weakly, in much the same fashion as the range-Doppler estimates associated with the output of the linear FM correlator. This interesting property is shown to depend on a single optical parameter. A modified optical configuration that enables a greater practical exploitation of this property is suggested. To obtain unbiased target range estimates, two output terms must be observed, but the range estimate thus obtained has a lower variance than the estimate obtained from either output.