GB864860A - Improvements in or relating to electrical apparatus for providing a measure of standing wave ratio in a high frequency electrical transmission means - Google Patents

Abstract

864,860. Impedance measurement; voltage measurement. GENERAL ELECTRIC CO. Ltd. July 24, 1957 [April 24, 1956], No. 12606/56. Class 37. Apparatus for indicating the standing wave ratio in a high-frequency transmission system comprises means for deriving a first signal dependent on electromagnetic wave energy in one direction in the system and a second signal corresponding to the reflected energy and means arranged to vary the second signal in dependence upon the first signal but so that the second signal does not vary with variation in energy of the electromagnetic waves, the second signal as varied in dependence on the first signal being a measure of the standing wave ratio. In the embodiment shown, a klystron oscillator 2 modulated by pulses from a modulator 1, sends signals along a waveguide 4, the frequency of oscillation being varied by motor 3. The waveguide is provided with directional couples 9, 10, 11, variable attenuators 7, 8, and is connected to the waveguide 5 to be tested and is terminated by a matched load 6. An incident electromagnetic wave in the forward direction will be propagated in arm 9a to wavemeter 12, in arm 10a to probe 15, and hence to rectifier 16 and amplifier 18 to control the gain of amplifier 23, and be absorbed by a matched load 19 in arm 11a, the reflected wave together with the incident wave setting up standing waves in the waveguide 4. The reflected wave is propagated in arm 11b, to rectifier 21 amplifier 22 and input terminal 23a of amplifier 23, and is absorbed by matched loads 17, 14 in arms 10b, 9b. The signal applied at 23a is thus amplified in depence on that applied to control terminal 23b and the gain of the amplifier 23 is so controlled that the signal appearing at output terminal 23c is independent of the variation of energy of the electromagnetic wave in waveguide 4 in the forward direction and gives a direct indication of the reflection coefficient (and therefore of the modules of the standing wave ratio) of waveguide 5 and varies directly therewith. The output signal is applied to unit 24 e.g. an oscilloscope or meter. An absorption-type wavemeter may replace meter 12. A construction of a controlledgain amplifier is described in detail (Fig. 2, not shown).