RADIO PHYSICS AND RADIO ASTRONOMY

Subject and Purpose. Proceeding from a mathematical model of the electronically tunable autodyne oscillator (Part І of this paper), essential features of the signal formation / signal processing procedure are considered, as implementable in an autodyne radar that may reveal nonlinearity in its modulation characteristic. The work is aimed at suggesting a digital technique to enable introduction of corrections to the frequency modulation law of the sounding signal and effectuate processing of the data from the close-range autodyne radar (improving its spatial resolution and accuracy of target range measurements).

Methods and Methodology. The present analysis of the radiated signal formation and processing of the data from the autodyne radar has been carried out as numerical modeling of spectral, frequency and amplitude characteristics of the radar signals expected,  as well as spectral processing of the experimental data from the frequency modulated autodyne radar.

Results. An eff ective law of temporal variations has been suggested for the corrective control voltage of the Gunn diode-based Ka-band autodyne transceiver with a linear law of frequency modulation. The correspondent experimental studies were conducted with an autodyne close-range radar system of Ka-band employing an asymmetric linear frequency modulation with a 500 MHz band of frequency tuning. The use of digital methods for correcting the frequency modulation law has permitted improving the accuracy of target ranging and range resolution up to 0.3 ÷ 0.6 m, which figures correspond to the theoretical limit for the close-range homodyne radar with a 500 MHz tuning band.

Conclusion. By linearizing the modulation characteristic of the oscillator and applying digital processing to the autodyne signal in the close-range radar system with a linear frequency modulation law it proves possible to reach ultimately high estimates for the accuracy and resolution of target range measurements. The results obtained can be helpful for developing radar sensors and radiofrequency meters with enhanced parameters and characteristics.

Keywords: autodyne, autodyne signal, frequency modulation, non-linearity of modulation characteristic, close-range radar, Gunn-diode oscillator

Manuscript submitted 15.12.2021

Radio phys. radio astron. 2022, 27(2): 121-128

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