Abstract :
Under the stimulus of developments in aeronautics, rocketry and spacecraft, radar technology has maintained the momentum of its advance. There is now a need to combine a range discrimination of, say, a few feet with pulse-modulation envelopes equivalent to several miles, and to combine very long unambiguous ranges with accurate Doppler information, good subclutter visibility and freedom from interference. The use of long pulses with wideband, within-pulse modulation permits high range discrimination and low pulse-repetition rates to be combined with high mean powers. Filters matched to these long modulation envelopes can combine the received energy coherently and transform it into an equivalent short pulse. At the same time they can, within a single received pulse, provide a measure of Doppler-selective filtering and of further Doppler measurement. Coherent integration over a succession of such pulses provides more accurate but ambiguous Doppler resolution, and the within-pulse coarse Doppler information can then resolve these ambiguities. The high resolution in the range and Doppler co-ordinates gives a corresponding improvement in the signal/clutter ratio. Various nonlinear operations can also discriminate against strong clutter obliterating part (but not all) of the desired signal. The paper discusses these problems and describes various phase-, frequency- and amplitude-modulation techniques, and the corresponding circuits for stretching short pulses into long, complex transmitter-modulation signals and recompressing the received signals into short pulses. A number of the concepts, techniques and circuits introduced are believed to be original.
