Pulse Doppler Radar 205 17.3 Doppler Ambiguities Doppler ambiguities can occur if the Doppler range is larger than the PRF. The maximum Doppler requirement of a given radar can be estimated. Let's use a military airborne radar example. The fastest closing rates are with approaching targets because speeds of both the radar-bearing aircraft and the target aircraft are summed. This should assume the maximum speed of both aircraft. The highest opening rates might be when a target is flying away from the radar-bearing aircraft. Here, we should assume the radar-bearing aircraft is traveling at minimum speed, and the target aircraft is flying at maximum speed. We should also assume the target aircraft is flying a large angle y from the radar-bearing aircraft flight path, which further reduces the radar-bearing aircraft speed in the direction of the target. Maximum positive Doppler frequency (fastest closing rate) at 10 GHz or 3 cm Radar-bearing aircraft maximum speed: 1200 mph ¼ 536 m/s Target aircraft maximum speed: 1200 mph ¼ 536 m/s Maximum positive Doppler ¼ 2 (1072 m/s) / (0.03 m) ¼ 71.5 kHz Maximum negative Doppler frequency (fastest opening rate) at 10 GHz or 3 cm Radar-bearing aircraft minimum speed: 300 mph ¼ 134 m/s Effective radar-bearing aircraft minimum speed with y ¼ 60-degree angle from target