Relationship of Signal and Noise Characteristics of Autodynes with Frequency Modulation as Function of Distance to Location Object

摘要

Abstract The paper presents the results of analysis of signal and noise characteristics of autodynes with frequency modulation. The mathematical model of autodyne is presented in the form of a self-oscillator with single-loop oscillation system that is frequency-tuned using the varicap. This model takes into account the impact of intrinsic radiation reflected from location object and the impact of generator internal noises on the oscillator. The paper investigates the relationship of the distortion degree of signal characteristics and the periodic nonstationarity of the root-mean-square value of the level of frequency and amplitude noises as a function of the distance to the location object and the value of external feedback parameter of the autodyne “generator–location object” system. It has been shown that at a small value of the parameter of external feedback, the signal characteristics are quasi-harmonic similar to homodyne type systems, while noises represent a stationary random process. If the value of external feedback parameter is comparable to unity, anharmonic distortions are observed in signal characteristics, while the periodic nonstationarity is observed in noise characteristics. It was established that with an increase of distance to the location object, when the delay time of reflected radiation became comparable or larger than the period of autodyne response, the degree of anharmonic distortions of signal characteristics and the height of peaks of root-mean-square noise level were significantly reduced. The results of experimental investigations have been obtained using the prototype of autodyne sensor with frequency modulation built on the 8-mm band Gunn diode.