E.V. Bogatyrev1, D.S. Vishnyakov2, K.A. Ignatkov3, O.A. Kuvshinov4, V.Ya. Noskov5

1 Siberian Federal University (Krasnoyarsk, Russia)
1 JSC «NPP «Radiosvyaz» (Krasnoyarsk, Russia)
2-5 Ural Federal University (Yekaterinburg, Russia)
1 bogatyrev-sfu@mail.ru; ²daniil.vishniakov.ru@gmail.com; 3 k.a.ignatkov@urfu.ru; 4 o.a.kuvshinov@urfu.ru; 5 v.y.noskov@urfu.ru

Autodyne oscillators (AO) are widely used as a transceiver in short-range radar systems (SRRS). The principle of operation of these devices is based on the autodyne effect, which consists in changes in the parameters of AO self-oscillations, such as the amplitude and frequency of oscillation, as well as the voltage or current of self-displacement on the active element (AE), under the influence of its own reflected radiation. As a useful signal, they use any of these changes in the form of low-frequency components of the autodyne response, which can be isolated in the AO power supply circuit by changing the AE current or voltage or by means of an amplitude detector connected to the resonant AO system.

The use of various types of radiation modulation (amplitude, frequency, or phase) significantly expands the functionality of autodyne SRRS and improves their performance characteristics. The article discusses the features of the formation of signal and noise characteristics of autodynes with pulse modulation (PM) of millimeter-wave radiation. In the case of PM, when the delay time of the radiation reflected from the target is less than the duration of the radio pulse, the reception process occurs simultaneously with the transmission of the probing radio pulse. In this case, the radiated and reflected vibrations are coherent and the allocation of a useful signal is based on recording changes in the pattern of their interference in the oscillator itself, that is, on its autodyne effect.

The purpose of this article is to present the results of the performed studies of the features of the formation of signal and noise characteristics of radio pulse AO. For this purpose, a generalized AO model is proposed in the form of a set of linearized differential equations in the vicinity of a stationary AO regime with a single-circuit oscillatory system for small relative changes in the amplitude and frequency of vibrations. It takes into account the time constants of changes (relaxation) of the amplitude of AO oscillations, its internal parameters (coefficients of autodyne amplification, non-isochronism and non-isodromity), as well as the delay time of reflected radiation. The methodology and results of a step-by-step calculation of the process of establishing an autodyne response and noise characteristics are presented. The process of forming a response is described with sufficient accuracy for practice by the method of steps using expressions obtained by the quasi-static method. The calculations were performed using the MathCAD software package under various initial conditions. First, the case of AO of a stationary reflector is considered, when in the expressions obtained, the delay time has fixed values. At the same time, the influence of the non-isochronous and non-isodromous AO, as well as the magnitude of the feedback parameter, on the formation of signal and noise characteristics is taken into account. Then the features of the formation of signals and noises in various areas of reflected radiation exposure are considered. The results of the performed experimental studies have confirmed the adequacy of the developed mathematical model of the autodyne system.

As a result of the performed studies of the radio pulse autodyne microwave oscillator, it was found that the transient process of establishing an autodyne response, starting with the effect on the oscillator of the first partial reflection of its own radiation from the location object, causes changes in the parameters of self-oscillations (frequency and amplitude) in accordance with the sinusoidal law. At the same time, the noise level at the output of the autodyne retains a constant value, determined by the intrinsic noise of the stationary mode of the autonomous microwave oscillator. At this step, pulse modulated autodyne SRRS maintain the linearity of the transformation of their own radiation reflected from the objects of the location. In terms of their properties, radio pulse autodynes at the first reception step are similar to homodyne systems in which the transmitter and receiver are decoupled from each other. This property is quite important for the practice of using radio pulse autodynes, since in this case the widest dynamic range of SRRS is also provided.

Subsequent reflections of electromagnetic radiation from the location object, when the feedback parameter is commensurate with unity, cause anharmonic distortion of the shape of the autodyne signal, as well as the appearance of periodic instability of the RMS noise level at the signal output of the autodyne microwave oscillator. This instability, which begins with the second exposure to reflected radiation, manifests itself in the growth and exacerbation of noise peaks, which correspond to the region of the greatest positive steepness of the frequency response of the autodyne.

The duration of the transient process of partial establishment of the autodyne response and noise characteristics when exposed to reflected radiation significantly depends on the value of the feedback parameter of the “oscillator – target” system. In the case when the value of the feedback parameter is significantly less than one, the formation of steady-state values of the autodyne signals and noise characteristics occurs immediately upon the arrival of the first reflection, and the signals have a harmonic shape, and the noise level is constant. In cases where the feedback parameter is commensurate with unity, the greater the value of this parameter, the longer the step-by-step process of establishing an autodyne response takes. In the case when the parameter value is greater than unity, partial reflections, starting from the second one, cause significant complications of the autodyne characteristics with loss of their periodicity, as well as an increase in unsteadiness and noise level.

The obtained research results, which significantly expand the known concepts of noise processes in radio-pulse autodynes, must be taken into account when developing signal processing algorithms and using radio-pulse autodynes in newly created millimeter-wave SRRS. We associate the prospects for further development of this area with the study of the possibility of using frequency-stabilized microwave oscillators as radio pulse autodynes, for example, with a high-quotient additional resonator or signal synchronization from an external low-power oscillator.

Bogatyrev E.V., Vishnyakov D.S., Ignatkov K.A., Kuvshinov O.A., Noskov V.Ya. Features of the signal and noise characteristics of radio pulse autodynes in the millimeter range. Achievements of modern radioelectronics. 2026. V. 80. № 3. P. 74–93. DOI: https://doi.org/10.18127/j20700784-202603-10 [in Russian]

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