A Two-Step Sequential Procedure for Improving the Cumulative Probability of Detection in Radars

Sequential detection procedures, which may be used with phased-array radars, can provide a significant improvement in search capability as compared to uniform scanning. This paper discusses the improvement in cumulative detection probability (the probability that an approaching target is detected before it reaches a given range) which can be obtained with the two-step sequential test, first described by Finn [6]. In this test, a first pulse is transmitted in each beam position. If a threshold crossing is observed in any range cell, a second pulse of higher energy is transmitted and the returns compared with a higher threshold. A target is declared present if and only if threshold crossings are observed on both pulses in the same range cell. Curves of cumnulative detection probability vs. range are given for a nonfluctuating target and for two of the target fluctuation models considered by Swerling [7]. Results are given for three values of range resolution, and the radar parameters that optimize performance are tabulated in each case. In practical cases where the range resolution is from one to ten percent of the range, the sequential test considered here yields an energy saving of 3 to 4 dB as compared with uniform scanning.