V.Ya. Noskov - Dr.Sc. (Eng.), Professor, UFU. E-mail: noskov@oko-ek.ru; evgeny@pavlov.name
K.A. Ignatkov - Post-graduate Student, UFU. E-mail: k.a.ignatkov@gmail.com
S.M. Smolskiy - Dr.Sc. (Eng.), Professor, MPEI. E-mail: smolskiysm@mail.ru

An equivalent circuit of an autodyne oscillator containing the main operating (active) resonator with which a load is connected and the high-Q stabilizing resonator with resistive coupling is considered to develop a mathematical model describing key processes in the system under investigation. An analysis of obtained equations for specified oscillating system showed that its frequency characteristics differ essentially from the typical characteristics realizing in the usual one-circuit oscillator. A presence of the sharp dip on the characteristic of oscillating system-s resistive conductance limits conditions of amplitude-s and phase-s balance in the frequency range and improves excitation conditions of single frequency oscillations. The slope of the reactive conductance function of oscillating system in an interception point of zero value characterizing the oscillator-s stabilizing ability in frequency is much more for stabilized oscillator compared with the single-circuit oscillator. Mentioned features of frequency functions of these oscillating systems - conductivities are taken proper account in main elations obtained in this paper, which describes the autodyne response upon the impact of own emission reflected from the object under investigation with consideration of natural noises of the oscillator. Calculations of phase, amplitude, frequency and amplitude-frequency characteristics of the stabilized autodyne system as well as spectral and noise characteristics are fulfilled under different conditions. Results of such researches, which were compared (during the material presentation) with results obtained for the usual non-stabilized autodyne oscillator, consist in the following. It is determined that main parameters of stabilized oscillators such as coefficients of auto-detection and autodyne amplification, are the same as for usual (non-stabilized) oscillators. Moreover, signal distortions peculiar to them are the same as for usual autodynes but the level of these distortions is significantly lower due to lesser values of autodyne frequency deviation, which widens essentially the dynamic range of the short-range radar. A degree of reduction of the frequency deviation and the distortion parameter of the stabilized oscillator is suggested to characterize by the stabilization factor, which shows how much the autodyne frequency deviation of the oscillator under investigation is less than for the usual oscillator at the same reflected signal-s level. In the autodyne oscillator stabilized by the external high-Q resonator the stabilization action is mainly demonstrated at exact tuning of this resonator to oscillation frequency of the autodyne. The frequency offset presence causes reduction of the stabilizing ability of this resonator, increase both amplitude and frequency sensitivity of the autodyne. In some cases this property of the stabilized autodyne can find application in various radiowave sensors and measuring systems, however, at that, the choice of its operating mode requires some compromise with stability conditions. Nonlinear distortions of the autodyne signal, which are observed at increase of the reflected emission level, in contrast to usual autodynes are caused by the frequency dispersion of the resistive conductance of the oscillating system. A nature of these distortions consists in the fact that at autodyne frequency variations the additional amplitude modulation occurs at each slope of the frequency curve with doubled frequency. This modulation is superimposed onto natural autodyne amplitude variations, which are caused by phase variations of the reflected wave. In the case of small values of the distortion parameter (we call this case "small signal") the function of the root-mean-square level both frequency and amplitude noises with regard to the relative distance to the reflecting object is practically absent. Nevertheless, in the case of the "large signal", when the distortion parameter is commensurable with 1, in the autodyne sensor we can observe the periodic non-stationarity of noise levels multiple to a half of the emission wavelength, which depends on the reflection surface position. At that, in one reflector positions the noise levels may noticeably decrease with regard of the "small signal" case, but at other positions - essentially increase. Thus, the more slope parts of autodyne frequency characteristics corresponds to noise level increase, but the more flats parts - to its reduction. Frequency stabilization of the oscillator facilitates to elimination of this non-stationarity of noise characteristics. We can slightly increase the system potential by introduction of some offset of stabilizing resonator frequency with regard of oscillation frequency since at that amplitude and auto-detection sensitivity of the autodyne to the reflected signal increases and the noise level keeps practically the same. Prospects of further autodyne investigations frequency-stabilized by the external resonator with resistive coupling relate to optimization of oscillator coupling with a resonator and a load for realization the largest energy potential of the system at the specified dynamic range of the reflected impact level as well as noise characteristics, at which analysis we take into consideration of the bias noise source for the active element. Moreover, it is interesting to study peculiarities of autodyne signal-s formation under conditions of the high level of reflected emission, as well as foreign experience in autodyne module development. These investigations are necessary for further improvement of autodyne quality indices and widening of its application area. Expediency of development and manufacture of new types of monolith and hybrid-monolith stabilized autodynes of millimeter-range is shown. We can use not only multi-meza Gunn structures as the active elements of these modules but the field-effect transistors as well, the oscillating frequency of which passed through terahertz boundary and new controllable oscillating devices with intervalley electron transition having, as we may expect, the decreased level of the natural noises. As oscillating systems of such autodynes we may apply structures integrated with high-Q resonance structures, for instance, in the form of distributed Bragg-s reflectors. The operation principle of these reflectors is based on the wave interference inside the waveguide with corrugated walls, which creates in the waveguide the resonant distributed feedback ensuring by this the single-frequency mode of oscillation and high spatial coherency of the emission. This structure widely used now in semiconductor lasers ensures, on the one hand, frequency stabilization due to its high frequency selectivity and, on the other hand, - the possibility of parametric "electronic" frequency control. The last property of Bragg-s reflectors in conformity with UHF oscillators can be used in autodyne modules for short-range radars with frequency modulation. In addition, integration of the autodyne oscillator and an antenna in the single microcircuit package allows creation of the one promising type of oscillating-radiated modules, which (having the decreased cost due to absence of waveguide elements) essentially widen the application area in realization of various short-range radars including with autodyne phased antenna arrays.