Estimation of Direction-of-Arrival by an Active Array

Recently, MIMO techniques have been using in active radars,and become a hot topic in radar field, where they improve the performance of detection and parameters estimation greatly. On estimates of direction-of-arrival (DOA) in active radars, generally elements of the receive array were closely spaced to enable direction finding measurements. However, in order to obtain angular diversity, all elements of active radars need to be sufficiently separated, and so targets are in the near field of the array. Therefore, estimates of DOA in the active radars are near-field problems in fact. This paper tries to study direction finding of active radars from near-field principle, and establishes near-field estimates of DOA model of active array systems. The near-field model needs only 1-D searches, and decreases the burden of calculation in comparison with the traditional near-field estimates of DOA, which generally need 2-D searches. From the Cramer Rao bound (CRB) analysis, we find that there is great improvement on the performance of DOA estimates.