Threshold of the Velocity Gate in a Continuous Wave Radar with Conical Scan Tracking

摘要

A study is made of the behavior of the velocity gate in a continuous wave radar with conical scan tracking. Adapting the analysis of the frequency modulation feedback demodulator (FMFB), two linear models are developed for the velocity gate. The first deals with the gate's response to a static doppler frequency offset and the second deals with its response to a varying doppler frequency. The dynamic model also incorporates the presence of narrowband, Gaussian noise at the input to the gate. The phase tracking error of the gate due to noise is determined as a function of the carrier-to noise ratio (CNR) in a bandwidth equal to the closed-loop noise bandwidth. Establishing the performance criterion to be the frequency tracking error, two definitions for the threshold of the gate are established. The first states the threshold occurs at the value of CNR for which the root-mean-square frequency tracking error due to noise exceeds half the 3db bandwidth of the IF filter within the gate. The second bases the threshold on the probability of the frequency error exceeding half the 3db bandwidth of the IF filter. Both definitions are applied to an example in which a second order velocity gate is considered. (Author)