8 - Air-to-Air Detection

Abstract

Air-to-air detection is the most difficult mission radar has to perform, especially when target is flying at low altitude and is mixed with strong ground clutter returns. The chapter discusses the three generations of radars that are range-unambiguous. Noncoherent radar is composed of the following: an antenna, a transmitter, a microwave signal mixer, a local oscillator, an IF receiver and the matched filter, an envelope detector, a constant-false alarm rate (CFAR), a post-detection integration, and a detection device. The purpose of CFAR device is to normalize the noise superimposed on clutter signals to independently determine the detection threshold of characteristics of this noise. In modern radars—that can process a large amount of data by digital techniques—the post-detection integration is performed by a sampled filter that performs a true integration from one interpulse period to the next, for each range cell. Target detection is obtained by comparing the output signal from the post-detection integration with the threshold fixed by the imposed false alarm probability. Low pulse repetition frequency (PRF) and noncoherent radar gives good results as long as clutter level is low with respect to the targets.