Electromagnetic compatibility of passive and active channels of integration radar systems

Subject and Purpose. The paper is devoted to the noise immunity problem of the receiving channel of the radiometer as part of an integration passive-active radar system. The aim is to improve the detection of low-contrast radar targets against the background of radio wave reflections from the underlying land or sea.

Methods and Methodology. The study was carried out by computer simulation using the equivalent circuit of the radiometer microwave filters. The suppression of target reflected signals interfering in the radiometer receiving channel was by means of the weighted summation of radiometric signals having passed through the filters of the main and mirror channels of the radiometer. In that case, the center frequencies of the filters were symmetric about the carrier frequency of the radar active part, and the complex transmittances of the filters were picked so (the weighting procedure) that they had equal moduli and opposite phases at that frequency.

Results. The research was conducted at the 8 mm band frequencies for typical parameters of frequency-selective circuits. The focus was on the transmission characteristics of the useful radiometric signal and on the suppression of the probing signal of the radar active part, various values of the center frequency spacing of the main and mirror channels of the radiometer were considered. Effects exerted on the above-mentioned characteristics by deviations of actual parameters of the filters from their design values were estimated.

Conclusion. It has been shown that a deep suppression of the probe signal at the radiometer input can be achieved along with a simultaneous high transmission level of the useful radiometric signal provided that the center frequency spacing regarding the main and mirror filters of the radiometer makes up 3...4 bandwidths of these filters. When the center frequency spacing measures 3...4 values of the filter bandwidth, the effect exerted by the deviation of actual filter parameters from their design values is found to be substantially less than for a smaller spacing.