Space‐frequency maximal ratio combining for low‐elevation radar target

Abstract

SUMMARYWhen tracking radar is used for tracking a low-altitude target, fading due to multipath propagation consisting of the direct wave and the waves reflected from the sea surface (or the ground) is generated so that tracking becomes difficult. In this paper, as a remedy to this problem, a space-frequency maximum-ratio combining method is proposed that combines frequency hopping with an array antenna. In order to reduce the size of the transmission and reception system, and also to reduce the computational overhead for maximum-ratio combining, a subarray configuration is used for the array antenna and the maximumratio combining is applied to the subarray. By means of computer simulation, the effects of the space-frequency maximum-ratio combining in the full DBF and in the subarray configuration are compared. It is confirmed that a power level higher than that in free space can be obtained by the proposed method under the constraint of a distance of 5000 to 40,000 m for a target at an altitude of 100 m (constant) by letting the frequency hopping range be 20%. It is also confirmed that the diversity gain degradation due to the subarray configuration is small.