An Adjustable Radar Cross Section Doppler Calibration Target

This paper describes the development of a simple low-cost adjustable radar cross section (RCS) Doppler calibration target. It consists of a small metal sphere attached to the diaphragm of an ultrasound transducer. It is shown that the effective RCS of the target is a function of the physical RCS determined by the size of the sphere, and the magnitude of the displacement introduced by the transducer. A simple Michelson's interferometer was constructed to determine the magnitude of these displacements, and a linear relationship between the applied sinusoidal voltage (at resonance) and the displacement is determined. Measurements made using a sensitive Doppler radar confirm the calculated RCS to an accuracy of better than 2 dB, and show that it can be adjusted over 20 dB by adjusting the transducer excitation voltage through one decade. These low RCS targets are ideal for testing radio acoustic sounding systems and entomological radars.