The loss in output signal-to-noise ratio (SNR) due to amplitude limiting is obtained for a radar circuit consisting of a bandpass limiter, coherent demodulator, matched filter, and moving-target-indicator (MTI) filter. The circuit is used in scanning MTI radars. The tandem connection of the limiter and coherent demodulator is a model for the saturation of the intermediate-frequency (IF) demodulator of an MTI radar. Results on special functions are used to obtain simple formulas for the loss in output SNR relative to a linear IF demodulator when the input SNR is less than -15 dB and the number of hits per 3-dB beamwidth exceeds 15.

Performance Degradation of MTI Circuits Due to Amplitude Limiting

Computer simulations are used to study the effect of envelope limiting on the performance of pulse-compression moving-target-indicator (m.t.i.) radar in the presence of clutter produced by stationary reflectors and nonstationary reflectors. It is shown that the use of pre-envelope concepts to deal with bandpass processes as complex lowpass envelopes enables efficient use to be made of high-speed fixed-point-computer fast-Fourier-transform (f.f.t.) techniques to investigate difficult nonlinear-radar-system problems.

Effect of envelope limiting in pulse-compression moving-target-indicator radar systems

A decision-directed delay-lock loop is described using the fast Fourier transform (f.f.t.) for cross-correlation, together with decisions based on maximum likelihood. The f.f.t. produces a complete set of lagged products of the received echo and the delayed replica of the transmitted signal. This enables the loop to realise a wide dynamic range. Another useful feature of the loop is that it has the ability to detect unlocking and to switch automatically between the modes of acquisition, tracking, and detection of unlocking and reacquisition.

C.M. Thorsteinson

Papers

Effect of envelope limiting in pulse-compression moving-target-indicator radar systems

Decision-directed delay-lock loop using fast Fourier-transform crosscorrelation