Electronic roll compensation system for a radar antenna

A simplified and reliable system for electronically controlling the angular position relative to an antenna axis of the ground areas from which radar signals are received and processed so that air-to-ground range may be measured accurately regardless of the roll angle of the aircraft in which the radar is mounted. In a radar silent lobing system in which lobing is done on reception of the transmitted signals, the roll compensation system provides direct current signals which are proportional to the sine and cosine of one-half the roll angle and which are selectively applied to the pole pairs of the azimuth and elevation poles of the ferrite modulator that is utilized in the lobing system. During range determining operations, first and second pole pairs each of an azimuth and elevation pole, or group of azimuth and elevation poles, are energized or selected during alternate lobing or pulse repetition frequency intervals. The system functions at any roll angle alpha by positioning the magnetic field of the modulator at alpha /2 degrees so as to shift the components of the modulator input so that the vector sum at the output will be vertical, resulting in a constant output being provided to the radar receiver regardless of the roll angle of the aircraft.