Patent GB-928130-A (GB)
Title: Phase measuring apparatus
IPC: G01S3/48
Filed: 1962-01-05
Abstract: 928,130. Radio direction finding; automatic phase control; frequency and phase discriminators. ELECTRONIC SPECIALITY CO. Jan. 5, 1962 [June 15, 1961], No. 610/62. Classes 40 (5) and 40 (7). A microwave phase measuring device comprises a pair of signal inputs feeding voltage dependent phase shifters whose outputs are respectively divided into first and second signals in quadrature one with the other, a pair of detectors producing outputs in accordance with the envelopes of input signals respectively receiving the vector sum of a first signal from a corresponding phase shifter and a second signal from the other phase shifter, a differencing circuit receiving the detector outputs to produce a signal representing the difference between the amplitudes of the vector sums, which after amplification is applied differentially to control the phase shifters, and phase adjusting means in one or other input channel to zeroize the control signal when in-phase signals of a given frequency are applied to the device; the overall loop gain of the retroactive system being large so that the central voltage represents the input signal phase difference. In Fig. 1 microwave signal inputs 11, 12 are applied to phase variable travelling wave tube amplifiers 21, 30 respectively energizing through phase adjuster 17 and directly the hybrid junction 40 so that for input at terminal 41 the output at 43 lags 90 degrees on that from 44 while for input at 42 the output at 44 lags 90 degrees on that from 43, without direct intercoupling of inputs 41, 42. The vectorially combined quadrature signals at 43, 44 are rectified at opposed crystal diode video detectors 51, 53 and the rectified envelope signals are applied in opposite senses to a resistance adding circuit 60 (Fig. 2, not shown) whose output is amplified and applied to a phase splitter 80 (Fig. 2, not shown) applying opposed control voltages to the helices of the travelling wave tubes. Phase adjuster 17 is set for zero control voltage for in-phase input signals, and it is shown that the control voltage represents the input phase difference in magnitude and sense. A voltage measuring instrument may be connected to terminal 86, and a cathode-ray oscillograph may monitor the control voltages at 84 superimposed on the helix supply voltage. The device may be applied to radio direction finding by coupling the inputs respectively to a two-antenna directional array, and it is shown (Fig. 3, not shown) that the phase difference is proportional to the cosine of the angle of arrival of a radio wave, independently of frequency. For frequency measurement (Fig. 4, not shown) an input signal is split by a hybrid network into two in-phase signals of which one is fed direct to an input while the other is fed to the other input over a delay line introducing a phase shift of an integral number of half wavelengths at the centre frequency of the measuring band, at which the phase adjuster 17 of Fig. 1 is set for zero output voltage at terminal 86. It is shown that deviations of frequency are then indicated in magnitude and sign by the output voltage.