GB1195828A - Improvements in or relating to Variable Phase Shifters - Google Patents

Abstract

1,195,828. Phase shifters. THOMSON CSF. 30 May, 1969 [31 May, 1968], No. 27484/69. Heading H1W. A variable phase-shifter comprises means for dividing an input signal into two components of constant relative phase and variable relative amplitude, and a circulator for vectorially adding the two components. As shown, the input signal is divided by a directional coupler 4 into equal amplitude components which are fed through attenuators 32, 33 and variable amplifiers 6, 11 respectively to ports 1 and 2 of a circulator 7 having an output port 8. Amplifier 11 is mismatched to the circulator 7 so that the signal proceeding in an anticlockwise direction from port 1 to port 8 is reflected at the output terminals of the amplifier. Taking into account the 90-degree phase shift of the coupler 4 and the subsequent difference in path lengths, the components U, U<SP>1</SP> arrive at the port 8 with a constant phase difference # and add to produce a signal R of phase #. It can be seen from the vector diagram that the phase of R varies with the amplitudes of U and U<SP>1</SP>, and that maximum variation occurs when either U or U<SP>1</SP> is reduced to zero. If the control terminals 12, 13 of amplifiers 6, 11 are fed by equal voltages in antiphase then, assuming identical amplifiers with linear response, U + U<SP>1</SP> = B where B is a voltage equal to the maximum value of U and of U<SP>1</SP>, and 9 varies from 0 to #. The amplitude of R does not, however, remain constant. To obtain an output of constant amplitude R, the amplitudes U and U<SP>1</SP> of the components must be equal respectively to Rsin (#-#)/sin # and Rsin#/ sin # (deducible from the vector diagram). To this end, the amplifiers are controlled by a modulator 36 and phase comparator 37. One of the signals fed to the comparator may be reference signal and the other may be derived from the output 8.