Phase modulator with low nonlinear distortion

In the paper results of an investigation of a phase modulator with linear segmental approximation of the trigonometric functions are given. Specific features of this modulator are high stability of the carrier frequency, large baseband bandwidth, and very low nonlinear distortion for maximum phase deviation of 90° or 180°. The investigation included computer simulations and experiments with the prototype modulator. The influence of the nonlinearity of the diode characteristics, of the temperature variation, and of the maximum phase deviation-variation is examined. In addition, procedures for the maximum phase deviation enhancement and for the optimisation of the modulator elements for given signal statistics are described.