Telecommunications and Radio Engineering

SYSTEM OF AUTOMATIC FREQUENCY CONTROL OF HETERODYNE OF THE RADAR RECEIVER WITH MAGNETRON TRANSMITTER

RESUMO

At present, pulsed magnetrons are leaders in the use in the radar transmitters which is caused by the need to generate powerful high-frequency oscillations and to provide a given coverage range. The disadvantages of magnetrons include a significant level of noise and difficulties in implementing frequency control. For this reason, when using automatic frequency control (AFC), problems arise in controlling the frequency of the pulsed magnetron. In view of this, the AFC of heterodyne of the receiver rather than the one of the magnetron is most often used. The heterodyne frequency is maintained such that the receiver is always tuned to the frequency of the received signal. The objective of this paper is to analyze the existing methods for tuning the heterodyne frequency of pulsed radars with a magnetron transmitter, to develop a concept for building a functional layout and its practical implementation. The functional layout of the automatic frequency tuning system of heterodyne in radar receiver with a magnetron transmitter is developed and described in the paper. A frequency discriminator is used in AFC. The frequency discriminator combines the advantages of a single-cycle circuit (simplicity of design and tuning) and a two-cycle circuit (an output voltage equal to zero at the given magnetron frequency, as well as compensation of variations in the amplitude of the input voltage and interference). The practical implementation of the developed system is presented upon the example of millimeter-wave band radar (40 GHz), where a Gunn diode oscillator with varactor frequency tuning is used as the receiver heterodyne oscillator. In this paper, the electric scheme of a new frequency discriminator and its amplitude-frequency characteristic are shown. An intuitive method was used to develop an electrical schematic diagram. The analysis of the developed scheme was carried out using the method of mathematical modeling. Conclusions are drawn about the novelty of the proposed concept of constructing the AFC of heterodyne radar receivers with a magnetron transmitter and its advantages in comparison with known solutions.