Improving Clutter Suppression in Navy Legacy Radars

New Navy missions in littoral regions have accentuated the need for improved radar performance in a heavy clutter environment. While new solid-state phased-array radars, currently under development, are specified to have a much improved clutter suppression capability, a large number of ships using older tube-based transmitters will continue to have a major role in Naval operations for years to come. For many of these radars, the ability to suppress clutter is limited by intra-pulse noise generated in the Crossed-Field Amplifiers CFA used as the final power amplifiers of the transmitter. The cost of replacing such transmitters with more stable and lower-noise alternatives is usually deemed much too costly. In an effort directed at improving clutter suppression in such Navy Legacy radars, without the need for major transmitter modifications, NRL has been pursuing the development of a new signal processing technique, referred to as transmitter noise compensation TNC. This technique compensates for intra-pulse transmitter noise, as well as power supply instabilities, by capturing and processing an accurate replica of each transmitted pulse in real time. Subsequently, through pulse-to-pulse comparisons, the measured transmit errors are used to derive a digital filter, which compensates for the transmitter instabilities in the digital signal processor DSP, thus improving the suppression of returns from strong clutter. A preliminary feasibility study proved that this technique should be capable of providing more than a 10dB improvement in clutter suppression. This paper describes the TNC technique and outlines the results of an experimental study on the ANSPY-1B radar aimed at demonstrating the practical feasibility of the TNC technique.