Echo frequency controller for airborne Doppler radar - comprises calculator to adjust transmission frequency as function of apparent speed to predetermine echo frequency

摘要

The system utilises a calculator which determines the ground doppler frequency as a function of the aircraft speed and the inclination of the antenna. The calculator provides an estimate of the apparent speed of points on the ground in the principle lobe of the antenna. This produces a signal whose frequency is equal to the Doppler shift corresponding to this apparent speed and is used to control a frequency controlled oscillator to control the transmission of pulses on a carrier frequency. The ground echos are received by the antenna and are applied to a mixer. A frequency discriminator produces a frequency difference signal which is filtered and applied to a summator for correction of the calculated ground Doppler frequency from the calculator. This correction thus closes the loop.