Low current vector modulator

A low current vector modulator for modulating the amplitude and polarity of a radio frequency (RF) signal, comprising:

• first and second hybrid couplers, each having an input port, an output port, a 0.degree. phase port and a 90.degree. phase port, and each having approximately equal characteristic impedances, where the input ports of the first and second hybrid couplers are each electrically coupled to an RF signal source generating an RF signal to be modulated, the impedance of the RF signal source being approximately equal to half the impedance of the first and second hybrid couplers;
• first, second, third and fourth variable resistance terminations, the first, second, third and fourth variable resistance terminations being electrically coupled to the 0.degree. phase port of the first hybrid coupler, the 90.degree. phase port of the first hybrid coupler, the 0.degree. phase port of the second hybrid coupler and the 90.degree. phase port of the second hybrid coupler, respectively;
• wherein the first and second hybrid couplers generate first and second output signals on respective output ports, which output signals vary in amplitude and phase with respect to the RF signal in response to changes in resistance of the variable resistance terminations;
• a third hybrid coupler, the third hybrid coupler having a first input port, a second input port, a 0.degree. phase output port and a 90.degree. phase output port, the third hybrid coupler being responsive to the first and second output signals and generating a third output signal which varies in phase and amplitude in response to changes in resistance of the first, second, third and fourth variable resistance terminations;
• and
• resistance varying means electrically coupled to the first, second, third and fourth variable resistance terminations for varying the resistance of the terminations.