Abstract: An unbalanced quadrature phase-shift keyed UQPSK modulator modulates two information signals onto mutually quadrature components of a carrier. If the carrier components differ from an exact quadrature relationship by an error angle, crosstalk orr distortion is introduced. The effects of such an error are ameliorated by a limiter following the modulator.

Abstract: An unbalanced quarternary phase-shift keying modulator provides relatively higher signal power for one of two signal information channels. The carrier to be modulated is split into two equal-amplitude, equal-phase portions, each of which is applied to a biphase modulator. Each of the information signals is also applied to one of the biphase modulators, for producing two equal-amplitude, phase modulated carriers, each biphase modulated by one of the information signals. The modulated carriers are applied to the ports of a quadrature hybrid coupler which is other than a 3 dB (equal-amplitude) coupler. In one embodiment, the coupler is a 7 dB coupler. The modulated carrier applied to the through port of the coupler appears with reference amplitude and phase at the output of the hybrid. The modulated carrier applied to the other or coupled port appears at the output with relatively reduced amplitude and a relative phase shift. In one embodiment, the phase shift is 90.degree..

Abstract: A predistortion circuit of the reflective type uses antiparallel-connected diodes for the desired amplitude and phase nonlinearity. If the signal applied to the diodes is of not of the correct magnitude, the desired nonlinearity will not be obtained. The magnitude of the signal applied to the diodes is increased or decreased as required by an impedance transforming circuit. The impedance transforming circuit is tuned for the frequencies of interest. The overall distortion is reduced by applying a direct bias to the diode pair.