Hybrid mitigation of distortion in digital arrays

Abstract

Radars and other RF systems are often used to detect weak signals in the presence of strong interference. Consequently, these systems must be designed to accommodate both (1) high SNR levels, and (2) high instantaneous dynamic range (IDR) levels. Recently, digital beam forming (DBF) techniques have been proposed as a means of improving both SNR and IDR. In a DBF system, high SNR levels can be produced by coherently combining many lower IDR transmit/receive (T/R) channels. However, this does not necessarily result in an equally improved IDR because distortion, which is introduced by the RF electronics within each T/R channel, could also be coherently integrated by the beamformer. The resulting integrated distortion could exceed the noise level at the beamformer's output, thereby limiting IDR improvement. This paper describes an approach to increasing the IDR levels achieved by digital arrays. The approach combines traditional DBF techniques with new IDR enhancement measures. Dynamic range enhancement is achieved through the use of two complementary processes: (1) decorrelation of spurs, phase noise, and various intermodulation products, (2) linearization of selected intermodulation products. This approach provides an efficient means for reducing the broad range of distortion products that typically limit IDR.