Spectral Characteristics of Radar Echoes from Aircraft-Dispensed Chaff

Experimental amplitude and phase measurements of radar echoes from chaff both in the wake of the dispensing aircraft (new chaff) and after the aircraft has left the area (mature chaff) are described. UHF and X-band coherent radars are used to obtain experimental data for both continuously-dispensed chaff and discrete chaff units. The mean radial velocity V0 and the velocity standard deviation Ov, of the chaff cloud are estimated from complex-envelope spectral density estimates. For mature chaff, Ov ranges from 0.3 to 1.2 ms-1. For new chaff, both Ov, and V0 depend on the position in the wake. At 150 m behind the aircraft, Ov varies from 2.0 to 2.7 ms-1 and at 450 m, Ov, varies from 0.8 to 1.5 ms-1. No apparent correlation between the magnitude of Ov and either radar frequency or chaff type is found. An expression is derived which shows the effect of conical scanning on the complex envelope spectral density.