GB1091941A - Ground clearance warning system - Google Patents

Abstract

1,091,941. Pulse radar. NORTH AMERICAN AVIATION Inc. Dec. 20. 1961, No. 45707/61. Heading H4D. A monopulse radar system is mounted in a low-flying aircraft to provide the pilot with visual warning signals when ground obstacles are approached. An imaginary clearance plane is considered to be positioned at a predetermined distance beneath the craft and signals are produced when obstacles protrude above it. Three separate adjusting signal voltages are applied to the radar receiver; the first is manually controlled and corresponds with the perpendicular distance of the craft from the clearance plane, the second is inversely proportional to the square of the slant range to the obstacle and the third is inversely proportional to the slant range. The second signal voltage is applied to the radar receiver amplifiers to render the gain independent of the range. The third signal is combined with the antenna angle of depression and the clearance height to form a function which is multiplied by the radar receiver sum channel output signal. Ths is then compared with difference channel output to provide the warning C.R.T. signal. The mathematical basis of the system employs the property of a monopulse receiver, in that the ratio of the outputs from the difference and sum channels is proportional to the angle of the reflected signal from the antenna axis. The signals proportional to the inverse range and inverse range squared are derived from a phantastron circuit energized by the transmitter pulses.