Radar system for terrain avoidance

Claim 1

AN AIRBORNE RADAR SYSTEM COMPRISING: (A) AN UPPER AND A LOWER BEAM-FORMING ANTENNA, THE AXES OF THE BEAMS FORMED BY SUCH ANTENNAS DEFINING, IN A VERTICAL PLANE, AN ACUTE ANGLE SUCH THAT THE TWO BEAMS INTERSECT EACH OTHER; (B) MEANS FOR SCANNING SUCH ANTENNAS IN AZIMUTH; (C) MEANS FOR TRANSMITTING, ON A FIXED DUTY CYCLE, PULSES OF ELONTROMAGNETIC ENERGY FROM THE UPPER BEAMFORMING ANTENNA; (D) MEANS FOR SEPARATELY PROCESSING REFLECTED ENERGY RECEIVED BY THE UPPER AND THE LOWER BEAM-FORMING ANTENNAS TO PRODUCE SIGNALS, INDICATIVE, RESPECTIVELY, OF THE AMPLITUDE OF THE REFLECTED ENERGY RECEIVED BY THE UPPER AND THE LOWER BEAM-FORMING ANTENNAS AND TO COMPARE THE AMPLITUDE OF SUCH SIGNALS; (E) MEANS FOR SIMULTANEOUSLY VARYING THE ELEVATION ANGLE OF THE UPPER AND THE LOWER BEAM-FORMING ANTENNAS UNTIL THE AMPLITUDES OF THE SIGNALS RECEIVED THEREBY ARE EQUAL; AND, (F) MEANS FOR INDICATING AS A FUNCTION OF THE AZIMUTH POSITION OF SUCH ANTENNAS, THE ELEVATION ANGLE AT WHICH THE AMPLITUDES OF THE SIGNALS RECEIVED BY SUCH ANTENNAS ARE EQUAL.