April 1, 2004 1CW Radar Simple CW Radar Gunnplexer Schematic 0 0.05 0.1 0. 15 0.2 0.25-1.5-1-0.500. 511. 5TimeAmplitudeTransmittedReceived0 0.05 0.1 0. 15 0.2 0.25-1.5-1-0.500. 511. 5TimeAmplitude of ft*ftTranmitted*R eceivedAverageApril 1, 2004 2 Applications Police radars, baseball speed gun, artillery-projectile muzzle velocity measurement, docking radars (ships, cars), airborne Doppler navigator, vibration measurement, flow measurement, ground speed of vehicles, monitoring of respiration in humans and animals. Characteristics • More sensitive to clutter – can’t use gating to ignore clutter • Direction of target with simple CW radar unambiguous • Matched filter considerations • FM-CW Radar for range measurement • Much lower peak power that equivalent pulse radar – hard for hostile electronic warfare receiver to intercept • Multiple antennas are often required (no circulator) Range detection with CW-FM radar In the figure, (a) is the frequency-time relationship of an FM-CW radar with triangular modulation. The received signal (dashed line) from a target at range R is delayed a time T=2R/c. ∆f is the frequency excursion and fm is the modulation frequency. In (b) is the difference (beat) frequency between the transmitted and received signals. One can show that for a stationary target: cfRffmr/4 ∆= If the target moves there is a Doppler shift fd the difference frequency is fr + fd during the first half and the fr-fd the second half of the modulation period. One can average over a modulation period and get the
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