V.Ya. Noskov, K.A. Ignatkov, S.M. Smolskiy
From positions of a general approach, the analysis of autodyne characteristic dependence upon the inherent properties of the UHF oscillator such as their non-isochronism, non-isodromic as well as the phenomenon of the “frequency detection” is fulfilled. For this, the generalized model of the single-tuned autodyne oscillator is considered, in which the action of a reflected wave is represented in the form of the variable load. For the case of small disturbances of a steady-state mode by the reflected radiation the linearized equation system is obtained for determination the relative variations of amplitude and frequency as well as the output auto-detecting signal.
This system solution allowed the fulfillment of calculations of key parameters such as coefficients of auto-detecting and amplification, the autodyne frequency deviation, distortion parameter of the autodyne signal and to draw the volumetric diagrams depending on non-isochronism and non-isodromic coefficients. Moreover, equations for the phase offset angles of the autodyne variations of amplitude and frequency of oscillations are obtained as well as the auto-detection signal under condition of the uniform reflector motion.
After normalization of the mentioned solutions, equations of autodyne characteristics are obtained such as phase, frequency, amplitude and bias voltage, calculations of which is fulfilled in accordance with the computer program in the environment of the mathematical package «Mathcad». Results of these calculations are presented in the form of graphs showing the form of the autodyne response at reflector displacement and the spectral analysis is executed. Also the harmonic coefficients, amplitudes of harmonic components of the spectrum and levels of averaged values of the autodyne response dependent on the reflection coefficient modulus at different distance from the reflected object and at inherent oscillator parameters.
Experimental investigations for inspection of the key conclusions of the theoretical analysis were fulfilled on the example of the modified oscillator module «Tigel-8M» of 8-mm range produced on the hybrid-integrated technology on the basis of the two-mesa Gunn diode. From comparison of the experimental data obtained with the appropriate calculations we may conclude that there is the qualitative correspondence between theoretical and experimental results.
As a result of the fulfilled investigations, it is stated that in result of the analysis of peculiarities of the autodyne characteristic formation at different levels of the reflected radiation there is a possibility of estimation of the inherent properties and parameters of an oscillator such as their non-isochronism and non-isodromic coefficients as well as the frequency detection.
It is stated also that in a case of the different sign of non-isochronism and non-isodromic coefficients the dynamic range of the autodyne can be increased by several dB compared with the isochronous oscillator. For more essential extension of the dynamic range, as it is shown in  it is expedient to use the frequency stabilization with the help of additional high-Q resonator. It is especially relevant for the millimeter and sub-millimeter waves.
Results of this paper are useful at interpretation the experimental results of autodyne oscillators, at examination of the autodyne signal formation as well as at parameter optimization of UHF oscillators intended for short-range radar systems.