Homodyne and autodyne configurations of short-range radar systems

The processes of useful signal formation in the short-range radar systems constructed on the heterodyne, homodyne and autodyne principles are considered. The mathematical fundamentals of the fulfilled analysis are described in brief. It is shown that the autodyne configuration is much more complicated for the examination compared to the heterodyne and homodyne configurations due to the necessity of taking into account its own re-reflected signal. To simplify the theoretical analysis, the examination of the autodyne effect is performed under an assumption of reflected signal smallness. The comparison results of the considered configurations, which show that the homodyne and autodyne signal processing in the usual Doppler short-range radar turns out similar, are given. However, the autodyne short-range radar configuration itself has its own specific peculiarities, which should be taken into consideration in practice. It is proved that in the autodyne configuration one can meet the accompanying frequency modulation of the probing oscillation. It appears even at the absence of the forced frequency modulation, which is widely used to improve the short-range radar noise immunity. It is found out that this accompanying frequency modulation at weak reflected signals does not affect noticeably on the autodyne converter operation. The main theoretical conclusions of this paper are in the good conformity with the published results

Theory of stabilized autodyne oscillators at the large reflected signal

Research results on autodyne oscillator stabilized by an external high-Q cavity are presented for the case of the large reflected signal, when amplitude of the reflected wave is commensurable with amplitude of natural oscillations. Expressions describing an autodyne response of the oscillator on the influence of the proper radiation reflected from a target are obtained. Calculations of amplitude, frequency and spectral characteristics of the autodyne system are performed. Conditions of exact tuning of the stabilized cavity are determined. Investigations of stabilized autodyne parameters at small distance to the reflected object are provided. It is shown that to expand the dynamic range of the autodyne system it is expedient to use the large coupling between cavities. Recommendations concerning practical application of the obtained results in the short-range radar are given

Modulation characteristics of microwave autodyne oscillators

General relations for the analysis of autodyne and modulation characteristics are obtained in the form of differential equations with the retarded argument. Solutions for characteristics of frequency response of autodyne variations of the oscillation amplitude and phase as well as the auto-detecting signal of UHF oscillator under influence of the proper reflected radiation are derived. The solution of the same equation system is given for frequency responses of the modulation deepness of oscillation amplitude and frequency as well as the auto-detecting signal in the case of the reflection factor modulation by the high-frequency signal. Calculations of autodyne and modulation characteristics are fulfilled at different values of inherent parameters of UHF oscillators. Non-isochronous and non-isodromous properties of autodyne oscillators are investigated. Phenomena of frequency auto-detecting are considered. A method for dynamic properties determination is substantiated according to its modulation characteristics at the oscillation amplitude registration. The results of theoretical analysis are confirmed by experimental data obtained on the example of hybrid-integrated oscillator of 8mm-range on the Gunn diode

Analysis of signals of stabilized autodynes

Results of the autodyne signal analysis of the self-oscillating systems stabilized in frequency by the external high-quality cavity are given. The coupling between the main and stabilizing cavities is realized on the basis of a pass-reflective filter with a resistive link. Mathematical equations are obtained describing an autodyne response onto impact of the own radiated signal reflected from a target. The analysis of phase, amplitude, frequency and amplitude-frequency characteristics of the autodyne system is fulfilled. The calculation of an autodyne signal spectrum is discussed. A new type of nonlinear distortions of an autodyne signal is examined, which is caused by a frequency dispersion of an oscillating system of the stabilized autodyne. Advantages of the stabilized autodyne compared to the usual single-tuned autodyne oscillator are shown

Determination of autodyne oscillator parameters by the beating method

The research results of oscillator internal parameters influence the features of dynamic autodyne characteristics formation in the case of external oscillator signal influence are presented. The equivalent circuit with a single-circuit oscillating system is considered as a model of the autodyne oscillator. Abbreviated equations are obtained by an averaging method and then they are linearized for small disturbances in a vicinity of the steady-state mode. The obtained characteristics for the beating mode are compared with characteristics of autodynes for short-range radar technology. The essential differences in behavior of the oscillator with acting the external oscillator and the oscillator with acting the own reflected signal have been found. The physical sense of the frequency dispersion phenomenon for the autodyne frequency deviation in the vicinity of hypothetical “zero” beating is discovered. The research results of dynamic autodyne characteristics in the frequency conversion mode of signals modulated on amplitude or frequency are given. It is shown that to suppress the spurious harmonics of the beating frequency, it is advisable to take additional measures for generated frequency stabilization in autodyne frequency converters, for instance, using the external feedback in the oscillator or using the external high-Q resonator. The adequacy of theoretical conclusions is confirmed by results of experimental investigations of the hybrid-integrated module of 8 mm-range made on the basis of the planar two-meza Gunn diode. Oscillator characteristics obtained by the beating method are compared with results of investigation fulfilled with the help of modulation characteristics. It is shown that errors in experimental determination of dynamic characteristics of autodyne oscillators caused by frequency limitations of a pin-diode typical for the modulation characteristic method can be eliminated. Problems of practical application of obtained results in real radar systems using autodyne oscillators are discussed

Opto-Electronic Oscillator with Mach-Zender Modulator

The non-standard opto-electronic oscillator (OEO) operation is discussed in the generation mode of a single-side optical harmonic on the base of external and internal modulation of the laser signal. The OEO mathematical model is formed basing on laser differential equations for the closed radiofrequency network. With the help of the model offered, the phase noise of OEO radiofrequency oscillations is analyzed. It is shown that phase noise reduction in the circuit with external modulation depends not only on the increased laser power and growth of the geometric length of the optical fiber, but on reduction of the laser phase noise

Synthesis and Analysis Non-recursive Rejection Filters in the Transient Mode

The non-recursive rejection filter (RF), which is improved with the purpose of transient acceleration at arriving of the passive interference edge caused by disturbing reflections from fixed or slow-moving objects, is synthesized by the state-variables method. The structural diagram is offered of the tunable RF in the transient with the purpose of improvement of signal extraction effectiveness from moving targets on the background of the passive interference edge. The comparative analysis is performed of RF effectiveness for fixed and tunable structure in the transient according to the criterion of the normalized interference suppression coefficient and the improvement coefficient of the signal-to-interference ratio. The essential increase of the signal extraction effectiveness from the moving objects on the background on the interference edge for the wide class of the spectral-correlation characteristics at RF structure modification

The Processing Algorithm for Wideband Signals Propagating in Media with Frequency Dispersion

The new processing algorithm for wideband signals, which are propagating in frequency dispersion media, is developed in the context of the ground penetrating radar technology. The mathematical substantiation of offered method is presented on the base of linear functional spaces. The method is described for calculation acceleration on the base of the recursive approach. Results of numerical modeling of this method are presented for electromagnetic waves propagating in frequency dispersion media at utilization of chirp pulse signals. The Debye model is used as the model of electrical medium properties. The frequency dispersion of losses in the medium is taken into consideration at modeling. Results of operation modeling of the ground penetrating radar are described. Results of this paper will be useful for the ground penetrating radar technology and the ultrasonic flaw detection