Patent GB-803520-A (GB)
Title: Improvements in and relating to means for determining the relative speed and direction of travel between the earth's surface and any arbitrary reference on a vehicle
Inventor: BERGER FRANCE BARNET
IPC: G01S13/60
Filed: 1953-09-14
Abstract: 803,520. Radar; aerials. GENERAL PRECISION LABORATORY, Inc. Sept. 14, 1953, No. 25391/53. Class 40 (7). An aircraft is navigated by comparing the frequencies of reflected radar signals from areas (e.g. of the earth's surface) spaced transversely to determine direction and from areas spaced in the direction of relative movement to determine speed. Microwave signals are radiated as three hollow conical beams, each of the antennae 12 being as described in Specification 803,519, and comprising a slotted waveguide 3a with dipoles 3 coupled to the slots, with the slots located in the underside of the waveguide so that the latter acts as a partial shield for the unwanted upper part of the radiation pattern. The radiation is produced by a combination of end-fire and broadside propagation, with one element directed aft and two elements directed forwards and to either side, the antennae 12 being stabilized by a gyro- 40 and corrected for drift by alignment with the true relative velocity vector. Figure 16 gives the outline of the system, with a pulse-modulated transmitter 11, ATR and TR tubes, antennµ 12 and crystal mixers 21 wherein the reflected signals are mixed with the output of a local oscillator 19. The resultant beat frequency signals from one forward-looking antenna and one aft antenna are mixed at 22, 23 to provide spectra of intermediate frequencies. Frequency trackers 24, 26 measure the centres of these spectra and convert them to square wave D.C. pulses which are compared in a servo amplifier 27 to control a motor 14 orienting the antenna assembly. Bearing may thus be indicated at 15 and an indication of true speed derived from the output of either of the trackers 24, 26. In the modulator transmitter, Figure 17, the 50 kc. output from a freerunning multivibrator 50. is fed through a delay network 51, a cathode follower 52, and a pulse forming network 53 to effect the pulsed output from a magnetron oscillator 54. The output from the oscillator 54 is coupled to the waveguides feeding the antennµ 72, 73, 74 by a magic-T waveguide coupler 67. The received signals are mixed at 90, 94, 95 with the output from a local oscillator 81, having a frequency controlled to differ from that of 54 by 30 megacycles per second, and detected and amplified for feeding to the frequency trackers. Figure 18 shows one of the frequency trackers, wherein the Doppler frequency input 130 is normally mixed at 140 with the output of an oscillator 141 to provide a 20 kc. output which is compared in a 20 kc. discriminator 143 to provide an error signal adjusting the oscillator 141. A second oscillator 158 is similarly adjusted to have the same frequency as the input 130, and is periodically substituted for the input 130 for a few seconds. An integrating network 145b, 145c, serves as a memory circuit for instants when there is no appreciable signal at 130, 145 being an amplifier. The frequency tracking circuits are shown in detail in Figures 19, 19b, 20, 21, wherein the local oscillator 141 is represented by a multivibrator circuit 200, 201, with control tubes 203, 204 to ensure starting. The output from this oscillator is amplified at 243, 244, and applied to a mixermodulator 271 and transformer 277, to which the input 130 is also applied through a mixer 291. The modulated output from a centre tap 281 is applied to the frequency discriminator 143 comprising a parallel tuning circuit, with maximum impedance at 20 kc., and an impedance-matching tube 312 to provide potentials at 322a, 322b differing by 90 degrees with the phase angle varying in sense and magnitude in accordance with departure from the resonant frequency. The signal thus appearing at 322a, 322b is amplified in cascade-connected amplifiers 326, 328 and 327, 329 and rectified at 342, 344 to control the servomotor 148 or 149. The second local oscillator, 158, Figure 19b, comprises a multivibrator 421 with control tubes 422, 423. In this Figure the circuit for switching the oscillator 158 alternatively the signal at 130 on to the mixer 140 is shown, comprising a multivibrator 470 and relay solenoids 409, 480, energized therefrom. Tubes 411, 412 and associated circuits disconnect the servomotors 148, 149 when the energy in the echo wave is unusable. The two frequency trackers 24, 26, have limiting amplifiers 420, 520, each comprising a double-diode clipper, 496, 497. The outputs L, R from these amplifiers are fed to a frequency comparator, Figure 21, at 523, 530, to diodes 526, 527; 528, 529 and a resultant rectified signal is applied to a differential amplifier 541 to actuate the servomotor 14.