MULTIFREQUENCY CW RADAR WITH RANGE CUTOFF

摘要

This invention is directed to a CW radar system having range cutoff capability to render it insensitive to targets beyond a preselected range. Three frequencies are sequentially transmitted and reflections from a relatively moving target received to produce three doppler frequencies. The doppler shifts on the highest and lowest transmitted frequencies are phase compared to indicate range between the target and the antenna, which is unambiguous out to a preselected range. By noting the leading-lagging relationship of these two doppler frequencies, phase can be used below the ambiguous range to indicate whether the target is approaching or receding from the antenna. The third transmitted frequency lies between the other two, and produces an additional doppler frequency which can be phase compared with either of the other two doppler signals. Since the carrier frequency difference is lower in this latter comparison, the ambiguity in indicated range will occur at a greater distance. The lower difference frequency can accordingly be used to generate an inhibit signal for targets which fall near or beyond the ambiguity point of the first, higher deviation range measurement channel. Alternately, the third doppler can be phase compared with both of the other two and the results averaged for signal-to-noise ratio improvement. The average long range thus obtained is then used to generate the long-range inhibit signal when the average long-range value is beyond the preselected range.