<title>Low-Loss Constant-False-Alarm Rate Processors</title>

Abstract

Constant-False-Alarm Rate (CFAR) processors are used when the interference characteristics are not known a priori or change with time. When the unknown characteristic is only the level of the interference, a common CFAR implementation is the normalizer. This processor obtains an estimate of the interference level by arithmetically averaging the outputs of the resolution cells adjacent to the test cell. The test cell output is divided by the average and the normalized output is independent of the interference level. Therefore, a CFAR action is obtained. The penalty associated with the need to estimate the interference level is that the signal-to-interference ratio (SIR) required for target detection increases over the SIR value required for a known level noise background. Conventional normalizing C FAR circuits use the same configurations when detecting targets in interference regions and in clear regions. The CFAR penalty incurred in the clear region can be reduced by using processors that recognize the region is clear so that normalization is not necessary. An analysis of the target detection performance for a particular modified CFAR processor is given. It is shown that the decreased CFAR penalty in the clear is coupled with an increase of false alarm rate in the clutter regions.