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On Connection between Nonlinear Distortions and Autodyne Response Transients in UHF Oscillators


V.Ya. Noskov, S.M. Smolskiy

This paper is devoted to the investigation results for autodyne response’s transient at oscillator switching-on, and dynamics of the signal nonlinear distortion variation in a radio-pulse autodyne. A small-signal autodyne model is used at the analysis on the basis of which a phase delay of the reflected radiation is assumed having much less amplitude compared to the steady-state oscillator amplitude. At this model application, we also assumed that the steady-state oscillation transient takes place during the negligibly small time period compared to the time delay value. These assumptions allow the application of quasi-static approach for finding out the solution of the given equation system, and for obtaining (by means of the step-by-step calculation) the final expressions in the closed form for the autodyne response phase, for oscillation frequency as well as for normalized amplitude and frequency characteristics of radio-pulse autodyne. It is found out from the analysis of the main autodyne characteristics that the steady-state oscillation mode of the radio-pulse oscillator is established after a series of the spasmodic oscillated variations of the oscillation’s frequency and amplitude. The duration of this process as well as its character depends first of all upon the value of a distortion parameter, a phase distance to the reflector, and the oscillator parameters. Furthermore, it follows from the analysis of the main autodyne characteristics that the degree of autodyne signal nonlinear distortion caused by the deformation of a phase response due to the autodyne frequency variations is changing during the autodyne response transient. At that, this process begins from the first reflected radiation influence where the nonlinear distortion is absent and the formation of the sine autodyne variations of frequency and amplitude take place. At this section of the transfer characteristic, the emitted and radiated oscillations of radio-pulse autodyne loose the mutual dependence which is caused at the further regions be the autodyne frequency variations. It follows from the fulfilled calculations that it is very important for the radio-pulse autodyne especially in millimeter band to ensure the stabilized frequency of an autodyne oscillator, for example, by means of external high-Q cavity or by the radio-pulse oscillator’s synchronization from the external low-power oscillator, as an example, on the basis of low-current Gunn diode. The experimental results in the form of oscilloscope patterns or the spectrograms of the autodyne signals for different influence zones of the reflected radiation influence confirm qualitatively the theoretically predicted waveforms and spectra of the autodyne signals. The research fulfilled for the autodyne response transients at switching-on the radio-pulse oscillator as well as the dynamics of nonlinear distortion (form and spectral structure variations) of the autodyne response allow the establishment of interaction of these phenomena and to find out the main laws of autodyne output formation. The results obtained can be used at determination oа requirements to the autodyne oscillator parameters and characteristics and at choice of signal processing algorithm of the promising radio-pulse short-range radar.

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