S.M. Smolskiy – Dr.Sc. (Eng.), Professor, National Research University «MPEI»; 

Deputy Director of the Institute of Radioengineering and Electronics, Moscow Power Engineering Institute E-mail: smolskiysm@mail.ru

K.A. Ignatkov – Ph.D. (Eng.), Associate Professor, 

Ural Federal University

E-mail: k.a.ignatkov@gmail.com

A.P. Chupahin – Post-graduate Student, 

Ural Federal University

E-mail: ccaapp1992@gmail.com

This review generalizes results of investigations of signals characteristics features’ formations which were performed during last years for the practically interesting  case of strong reflected signal, when its’ amplitude is commensurable with the amplitude of the proper oscillations. Such a situation can be met in the short-range radar (SRR) systems at small and very small distances to the reflecting object.

The point reflector model was considered as a radar object. The autodyne equivalent circuit is presented by the parallel connection of the single-circuit oscillating system and an active element with negative conductance. The equation system is obtained describing the autodyne signal formation in the vase both weak and strong reflected emission.

At a choice of initial analysis data we take only those from them, which provide the smoothness conditions preservation of response formation. Such the conditions are provided at short ranges to the reflector, where the usually great level of reflected emission is observed. The analysis of such a case is fulfilled with involving of numerical methods based on the developed autodyne mathematical model. At the end of this review, as an example of the hybrid-integrated oscillator of the 8mm-range Gunn diode, we describe experimental investigations, which results qualitatively confirm the theoretical conclusions. These main results consist in the following. From the analysis fulfilled of the dependence of oscillator load conductance upon the phase of the reflection factor we state that the main reason of anharmonic distortions of the autodyne response is the load «nonlinearity». In the case of small signal, when the reflection factor modulus is significantly less than 1, the load variations are practically sinusoidal, and the deterministic role in formation distorted signals belongs to processes related to irregularity of the phase incursion in reflected emission.

As a result of the numerical analysis of the autodyne nonlinear model, it is shown dependences of harmonic coefficients, amplitude levels of harmonic components of the spectrum and the mean values of the autodyne response upon the reflection factor modulus and the distance of the radar object, as well as the inherent autodyne properties. Also, we investigated a behavior of autodyne system feedback parameter depending on the level of the reflected emission and a distance to the radar object. At that, we discovered that at strong reflected emission, the boundary value of the feedback parameter, at which the jumps in the autodyne signal occur, is less than 1.

The reasons of such deviation from the known condition are related with features of the nonlinear behavior of the load reverberation factor. This phenomenon must be considered at calculation of the maximal action range and the dynamic range of the autodyne SRR. Our results are represented as useful for interpretation of autodyne signal formation features and experimental results, at calculations and their optimization of their parameters and characteristics.

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