360° Varactor Linear Phase Modulator

Theory is presented which 1) derives the circuit impedance requirements to match the nonlinearity of the varactor reactance-versus-voltage curve to the tangent θ curve to obtain 180° linear phase modulation from one diode; 2) gives the value and position of a resistor to make insertion loss invariant with phase; and 3) derives the circuit requirements for combining two 180° diode phase moduIators in an admittance adding network to obtain 360° phase modulation. Experiments are disclosed rising series tuning at 1 GHz providing 360° phase modulation within ± 3.0 percent of linearity, and using shunt tuning at 5 GHz providing 360° phase modulation within ± 3.3 percent of linearity. A discussion is given of the application of the modulators to the serrodyne function.