Active phase and amplitude modulator

DETAILED DESCRIPTION These and other objects are obtained by replacing the variable resistor-reflective hybrid modulators with four amplifiers each amplifying one quarter of the input carrier, but with a phase that is in quadrature with two of the other amplifiers.
One phase of the four phases of the quadrant is supplied to each amplifier input.
A quadrature hybrid divides the input carrier into two outputs and differentially phase shifts the two outputs by 90 degrees.
These outputs are in turn divided in two by 180 degrees hybrids.
Four phases of the carrier are thus available to drive the amplifiers.
The gain of each amplifier is controlled by an independent modulating signal (MV).
The outputs of all four amplifiers are summed together.
The phase and amplitude of the resulting output is dependent on the contribution of each of the amplifiers.
No more than two amplifiers need be in use at the same time.
As a further refinement each amplifier consists of a push-pull pair of FET amplifiers, providing cancellation of even order distortion products.
Control of the gain of each of the four amplifiers is exerted by varying the gate bias voltage of each pair of FETS.