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Autodyne Effect in Oscillators with Amplitude Modulation


V.Ya. Noskov, S.M. Smolskiy

The general equations for the autodyne effect analysis are suggested for oscillators with an amplitude modulation (АМ) at the arbitrary modulation function law an at the arbitrary delay time of the reflected signal. Here the autodyne model developed earlier by the authors in the form of the single-circuit oscillator on the active element with the negative conductance and with the single-order auto-bias circuit is considered. To describe the autodyne effect which can be examined as the additional variations of the oscillation amplitude and frequency as well as a auto-bias voltage under influence of the own reflected oscillation, the system of the linearized differential equations with the retarded argument is used which is correct for the AM autodyne as well. The solution of this system is obtained in the quasi-static approximation when the processes of the oscillation parameter variations at simultaneous modulation and the reflected oscillation influence pass rather slowly and therefore, we can neglect the derivatives in the left parts of the differential equations. The first items in the obtained expressions for the autodyne variations of oscillation amplitude, frequency and auto-bias voltage represent the formation the parasitic components in the response at the output of the autodyne oscillator which repeat the modulation function, but the second items represent the useful components of the autodyne response in which there is a useful information about the distance and the velocity of the reflected object. Thanks to expansion of the delayed influence functions into Taylor series of the small parameter of the delay time, these equations describing the dynamics of the autodyne variations of the reflection factor with account of the simultaneous variations of amplitude and frequency of the radiated and reflected oscillations, become solvable with respect of all variables included. On the basis of the equations obtained, the numerical analysis is fulfilled for the peculiarities of autodyne AM oscillator’s behavior for the sine modulation function. To fulfil there examinations, the additional approximation was supposed concerning the real functioning conditions of the autodyne systems. The families of the normalized patterns for the characteristics of the target selection functions, the phase characteristics, the time and spectral diagrams of the autodyne response, and the generalized amplitude-frequency characteristics of the AM autodyne for various values of AM deepness, time delay, and oscillator parameters are considered. Experimental investigations conducted on hybrid-integrated oscillators TIGEL-08M on the double-meza Gunn diode confirmed completely the theoretical conclusions. As a result of the researchers fulfilled, it is shown that in the autodyne AM oscillator the autodyne response has the distortions due to the autodyne variations of oscillation frequency, which is similar to the usual (without modulation) autodynes. The presence of the autodyne signal distortion requires its own account at choice of the autodyne oscillator parameters and of the signal processing devices. The distinctive peculiarities of the AM autodynes consist in the fact that the autodyne response can be transferred as well to the modulation frequency harmonics in which connetion the effectiveness of such transfer is increased for the modulation deep growth and depends on the distance to the reflected object. Thanks to it, the AM autodynes on the modulation frequency harmonics have the property of the amplitude selectivity of the reflected objects at definite distance, which increases the noise immunity of the short-range radar on its basis.

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