Patent GB-965326-A (GB)
Title: Tactical radio landing system
IPC: G01S1/42
Filed: 1962-10-30
Abstract: 965,326. Aircraft radio landing systems. GENERAL PRECISION Inc. Oct. 30, 1962 [Nov. 29, 1961], No. 40963/62. Heading H4D. An aircraft landing system comprises a ground based radio transmitter with radiating means radiating a signal beam, means for conically rotating the beam about a selected axis at a selected rate of rotation and means for introducing a frequency modulated component into the signal beam, and, on the aircraft, a receiver including an amplitude modulation detector, a frequency modulation detector, phase detector means having the outputs of the amplitude and frequency modulation detectors applied thereto, and indicator means energized by the output of the phase detector means. As particularly described, the transmitter comprises an antenna 13, Fig. 1, rotated at 498 revs./s. by a motor 14 via gears 16 to produce a 1 degree wide beam scanned in a conical path 48, Fig. 5, having a 1 degree apex angle. The motor 14 also drives a potentiometer generator 17 to frequency modulate the output of a 10 kc./s. generator 19 at 498 c/s., the thus frequency-modulated signal is used to amplitude modulate the output of a microwave generator 11, the resulting signal being then radiated by the antenna 13. In the aircraft receiver, Fig. 2, the radiated signal is received and detected to obtain the 10 kc./s. frequency modulated signal. The said signal is also amplitude modulated at 498 c/s due to the rotation of the beam. The phase difference between the 498 c/s. frequency modulation and the 498 c/s. amplitude modulation depends on and determines the angular position of the aircraft with respect to the axis of the conical scanning paths whilst the amplitude of the 498 c/s. amplitude modulation determines the distance of the aircraft from the scanning axis. The amplitude modulation is detected at 26 and passed to an amplifier 29, tuned to 498 c/s. and to an A.G.C. circuit 28, having a time constant long enough to leave the 498 c/s. amplitude modulation unaffected, to control the amplifier 23 to compensate for changes in intensity in the received signal. The frequency modulation is detected in discriminator 33, the amplitude modulation being removed by limiter 32, and the resulting 498 c/s. signal passed to a second tuned amplifier 36. The outputs of the two tuned amplifiers are passed directly to a first phase detector 37 and, with a 90 degrees phase shift introduced in the output of amplifier 36, to a second phase detector 38. The output from amplifier 36 may be represented as being a vector quantity of fixed direction 43-19 and of fixed length, whilst the output from amplifier 29 may be represented as being a vector quantity of variable direction corresponding to the aircraft's angular position and a length representative of the aircraft's distance from the scanning axis 43. The phase detectors 37 and 38 are designed to give outputs representing the projection of the variable vector on the constant vector, the output from detector 37 thus represents the vertical deviation of the aircraft from the scanning axis 43 whilst the output from detector 37 represents the horizontal deviation of the aircraft from the scanning axis. The two outputs are used to respectively energize the movements of a crossed pointer indicator 41, the crossover point of the pointers thus representing the aircraft's position within the scanning circle 48.