V.Ya. Noskov, K.A. Ignatkov, S.M. Smolskiy

The analysis of known calculation methods for autodyne parameters and characteristics fulfilled in the present paper on the basis of developed mathematical model of the single-circuit UHF oscillator being under influence of the own reflected radiation showed that the widely used quasi-static method (of zero approximation) ensures the satisfactory accuracy of engineering calculation of the autodyne response in the frequency range of 20%-order from the cutoff frequency. At that, such features of the autodyne UHF oscillators as frequency dispersion of the autodyne deviation of the oscillation frequency did not take into consideration and, besides, application of this method is limited by condition of time delay smallness of reflected radiation compared with the period of the autodyne response. On the basis of fulfilled analysis, the new improved quasi-static calculation method for dynamic autodyne characteristics having higher accuracy of calculations and taking into account both the external inertia properties related to radiation propagation time to reflecting object and back and its internal inertia property caused by the finite relaxation time of oscillation amplitude. This method, which does not require integration of differential equations of the self-oscillating system, takes into consideration the specific distortions of the autodyne response caused by autodyne variations of oscillation frequency and the frequency dispersion of its deviation. At that, the analysis of external dynamic properties showed that with distance growth to the reflected object at high speed of its movement, when time delay of reflected radiation and the period of the autodyne response become commensurable variables, the degree of signal distortion, which is characterized by the equivalent distortion parameter, decreases. At the same time, the dependence of distortion degree of the signal shape both upon reflected object displacement speed and its movement direction can be determined from the analysis of internal dynamic characteristics of non-isochronous UHF oscillators. Such inherent properties of UHF oscillators as non-isochronous property, non-isodromic property, frequency detection, under conditions of fast reflector displacement influence on additional (dynamic) phase offsets of the autodyne response components. Influence of such inherent properties upon the autodyne response shape at high speeds is demonstrated only in the conditions of large values of equivalent distortion parameters commensurable with 1. Application of the improved quasi-static method provides essential reduction of calculation error of autodyne characteristics at essential widening of the Doppler frequency range as well as takes into account the mentioned dispersion function of the autodyne frequency deviation. The analysis on fine features of autodyne signal generation in devices of its processing with account of stability conditions provides widening of the dynamic range of short-range radar by 10-20 dB as well as increase the measuring accuracy of movement parameters of reflecting objects and functional possibilities of the system, for example, due to determination of object movement direction. Results of dynamic characteristic researches can be used at signal calculation not only the autodyne UHF oscillators but the laser measuring systems for object-s speed as well, which can be characterized by conditions, in which delay time of reflected radiation and the autodyne signal period are commensurable at usual movement speeds and distances to objects [8]. So, for example, at laser wavelength near 900 nm for the object speed about 10 m/s the autodyne signal frequency is about 20 MHz at its output. At that, for distance 10 m only the signal period Ta = 45∙10-9 s is less than delay time of reflected radiation τ = 55,7∙10-9 s. Formation of dynamic modulation characteristics of UHF oscillators is considered for variation of the reflection coefficient, bias modulation on the active element and for influence of the external UHF oscillation from the outside source in the beating mode taking into consideration the inherent properties of these oscillators such as non-isochronous property, non-isodromous properties and the frequency detection at high values of frequency of parameter variations. The analysis of obtained characteristics showed that the characteristic of amplitude modulation only coincides with the amplitude autodyne characteristic of the oscillator and can be used for determination of the time constant of the autodyne response, which characterizes the dynamic properties of the autodyne. At that, frequency and auto-detecting characteristics of the oscillator nave no mutual typical features for application with the mentioned aim. From results of fulfilled analysis it also follows that the process of autodyne response generation in the power source circuit at simultaneous modulation in this circuit depends practically upon all inherent parameters of the UHF oscillator, the operation mode, active element-s properties and external effects. At the same time, when using the external detector for output signal extraction, a number of influencing factors is noticeably less. This circumstance should be taken into account at designing of perspective autodyne modules intending to wide application in various systems. Fulfilled experimental researches of dynamic characteristics of autodyne oscillators - Tigel-08M - by different approaches showed that all of them demonstrate closed results at determination of the time constant of the autodyne response but higher measurement accuracy and simplicity of measuring the characteristics of frequency functions by beating method are additional advantages. This property is especially important during fulfillment laboratory investigations of a great number of various oscillators with the purpose to select of a type and to optimize the oscillation mode of autodyne oscillators. Results of experimental investigations of modulation characteristics allowed estimation of the time constant of the autodyne response of the hybrid-integrated oscillating module - Tigel-08M?. At that, it is shown that autodyne short-range radars of the millimeter range on Gunn diodes can operate successfully in the whole range of realized movement speeds of reflected objects. Results of fulfilled experimental investigations of transistor autodynes of the centimeter range give the positive answer to a question about principal possibility of replacement of super-regenerative receivers-transmitters to autodyne modules in the perspective systems of atmosphere radio-sensing. In these systems the autodyne oscillator together with the fulfilled function of the radio telemetric transmitter for atmosphere condition provides the sufficient operating speed at reception of radio pulses of the enquiry radar to ensure the required accuracy of distance measurement to the ball-probe.