| 摘要 |
945,548. Radar altimeters. UNITED AIRCRAFT CORPORATION. March 15, 1960 [May 11, 1959], No. 9044/60. Heading H4D. Relates to a pulse radar altimeter comprising a transmitter 18 and receiver 32 coupled through a duplexer 20 and switch 22 to a directional aerial 14 producing a beam directed downwards towards the ground ahead of of the aircraft, Fig. 1 (not shown), in which a voltage proportional to the intensity of the echo signal is subtracted in a comparator 64 from a voltage representing a predetermined fraction of the intensity of the transmitted signal to give a command signal representing the deviation of the aircraft from a predetermined altitude relative to the terrain ahead of the aircraft, said predetermined fraction being determined by the manual setting of a potentiometer 58; the command signal may be applied to automatically control the altitude of the aircraft. According to the present invention errors due to variations in the reflectivity of the terrain are compensated by automatically controlling the potentiometer 58 by a control signal representing the deviation of the aircraft from a predetermined altitude as measured relative to the terrain directly beneath the aircraft by a conventional radio altimeter 68 whose operation is independent of the reflectivity of the terrain. As shown, the control signal is derived in a comparator 76 as the difference between the voltage from a manually set potentiometer 80 representing the predetermined altitude and the output from the radio altimeter 68, the control signal being fed to a servomotor 90 controlling the potentiometer 58. The voltages representing the intensities of the transmitted and echo signals produced by the radar 18, 32 are obtained by alternately coupling the output from the receiver 32 to two integrators 44, 46 by means of a switch 34, the output from the transmitter 18 being alternately coupled to the aerial 14 and an echo box 30 by a switch 24 synchronized with the switch 34. Switches 24 and 34 may be waveguide switches. |
