V.Ya. Noskov1, E.V. Bogatyrev2, R.G. Galeev3, K.A. Ignatkov4, D.S. Vishnyakov5

1,4,5 Ural Federal University (Ekaterinburg, Russia)

2 Siberian Federal University (Krasnoyarsk, Russia)

3 JSC «NPP «Radiosvyaz»; Department of Radiophysics and Special Electronic Equipment of the M.F. Reshetnev SibSU (Krasnoyarsk, Russia)

1 v.y.noskov@urfu.ru, 2 bogatyrev-sfu@mail.ru, 3 krtz@mail.ru, 4 k.a.ignatkov@urfu.ru, 5 daniil.vishniakov.ru@gmail.com

In short-range radar systems (SRRS), autodyne oscillators (AO) are widely used as a transceiver. The principle of operation of these devices is based on the autodyne effect, consisting in changes in the parameters of AO self-oscillations, such as the amplitude and frequency of generation, as well as the voltage or current of auto-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 current or voltage of the AE 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 the autodyne SRRS and improves their tactical and technical characteristics. The article considers the cases of simple pulse modulation (PM) of radiation and the case of more complex modulation, when both pulse and frequency modulation (FM) simultaneously affects the AO. 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 receiving process occurs simultaneously with the transmission of the probing radio pulse. In this case, the emitted and reflected oscillations are coherent and the allocation of a useful signal is based on the registration of 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 the autodyne response of radio pulse AO both at constant and at varying frequency of self–oscillations.

For this purpose, a generalized AO model is proposed that takes into account both the external and internal inertia of the «oscillator – location object» system. The model is obtained 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 oscillations. It takes into account the time constants of changes (relaxation) of the amplitude of AO oscillations, its internal parameters (coefficients of autodyne gain and non-isochronicity), as well as the delay time of reflected radiation. The methodology and results of step-by-step calculation of the process of establishing an autodyne response are presented. The calculations were performed using the MathCAD mathematical software package under various initial conditions. First, we consider the case of AO in the absence of FM and the presence of a fixed reflector, when in the expressions obtained, the delay time has fixed values. At the same time, the influence of the non-isochronous AO, the values of the time constant of the autodyne response and the magnitude of the feedback parameter on the formation of the autodyne response is analyzed. Then the cases of the presence of FM generation of AO with a stationary and moving reflector, when the value is variable, are considered. The next object of analysis was the behavior of the amplitude of autodyne changes in the amplitude and frequency of AO oscillations in conditions of both moving and stationary object location. At the end of the section, the features of signal formation in various zones of reflected radiation exposure are considered and the relationship between the level of nonlinear distortions of the autodyne signal and the number of partial reflection exposure is established.

The results of the experimental studies have confirmed the adequacy of the developed mathematical model of the autodyne system in relation to the analysis of autodyne characteristics both under conditions of quasi-statistically slow and fast movements of location objects.

As a result of the conducted studies of the features of the formation of the autodyne response of radio pulse generators, it was found that the transient process, starting with the first reflected radiation acting on the generator, initially causes changes in frequency and amplitude in accordance with the sinusoidal law. At this step, autodyne radars are similar in their properties to homodyne systems, keeping the linear transformation of their own radiation reflected from various objects. The duration of the transient process and the features of the partial formation of the autodyne response under the influence of subsequent reflected radiation significantly depend on the feedback parameter of the «oscillator – location object» system.

The boundary of the fundamentally different nature of the generated autodyne signals is the equality of the magnitude of the feedback parameter to one. When the value of this parameter is less than one, the oscillatory process of establishing an autodyne response ends with steady-state values of the self-oscillation parameters, and when the feedback parameter is greater than one, the establishment process can be accompanied by abrupt and hysteresis changes in the amplitude and frequency of generation. This phenomenon in the latter case, even with uniform movement of the reflecting object, can cause anharmonic autodyne distortion of signals. To expand the dynamic range of a radio pulse autodyne and reduce the transient process of establishing an autodyne response, it is necessary to use stabilization of the generation frequency using, for example, a frequency-controlled external high-frequency resonator or synchronization from an external low-power source. An additional FM oscillator made on a low-current planar Gann diode can be used as a source of such a signal in a promising hybrid-integral autodyne module.

In the case when the distance between the radio pulse SBRL and the reflecting object is sufficiently large, and the Q-factor of the oscillatory AO system has relatively small values, so that the delay time of the reflected radiation significantly exceeds the characteristic time  of establishing an autodyne response, the influence of inertia of changes in the amplitude of oscillations in the analysis of the features of the formation of an autodyne response can be neglected. The process of forming a response in this case is described with sufficient accuracy for practice by the method of steps using expressions obtained by the quasi-static method.

In the case of small distances between the SRL and the reflecting object and high Q-factor values of the AO oscillatory system, the inverse ratio of the mentioned values is performed:. In this case, the process of establishing the autodyne response is completely determined by the characteristic time constant, and its analysis can be performed on the basis of a system of ordinary differential equations in which all variables are defined at the same time. The problem of analyzing the dynamics of the formation of an autodyne response in the case when the values and are commensurate is solved in the general case according to the methodology developed above.

It should be noted that from the analysis of transients in a radio-pulse autodyne by a quasi-static method, a conclusion was previously made about the expediency of using an external high-quotient resonator in the AO. Such a solution, of course, contributes to the expansion of the dynamic range of radio pulse SRRS, reducing distortion of the output signal and reducing the time to establish instantaneous values of the autodyne response. However, it follows from the results of this work that an increase in the equivalent Q-factor of the oscillatory system delays the transient process of establishing the amplitude values of the autodyne response, that is, the autodyne does not have time to fully «react» to the next radio pulse reflected from the object that has entered the AO resonator. For this reason, in «high-speed»: SRRSs, in which the time to make a decision on target detection is limited, when choosing the type of AO, the method of signal extraction and the algorithm for its processing, it is necessary to resolve this contradiction.

Thus, the performed studies of the dynamics of the establishment of an autodyne response, taking into account the inertia of changes in the amplitude of oscillations, significantly expanded the known ideas about the processes occurring in radio pulse AO with FM when exposed to their own reflected radiation.

Noskov V.Ya., Bogatyrev E.V., Galeev R.G., Ignatkov K.A., Vishnyakov D.S. Modern hybrid-integrated autodyne oscillators of microwave and mm-wave ranges and its applications. Part 17. Transients of radio-pulse autodynes. Achievements of modern radioelectronics. 2023. V. 77. № 11. P. 5–36. DOI: https://doi.org/10.18127/j20700784-202311-01 [in Russian]

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