Adaptive beamforming of multifunction radars in realistic multipath environment

Abstract

The ship-borne radar system has been faced with increasing demands for reacting against the evolved threats such as supersonic anti-ship missiles, low flying targets, and low radar cross section targets. As a consequence, modern radar systems require numerous functionalities and great flexibility in order to support dedicated missions and to protect ship from these threats, thereby employing a phased array multifunction radar. Regarding ship self-defense, detection and tracking of low altitude fast threats are of the greatest importance. However, since target tracking over the sea surface is seriously affected by multipath, it is important to find efficient method to resolve the problem. In this dissertation, three subjects will be considered to be involved in the enhancement of performance for a phased array multifunction radar system. The subjects have close correlation among them and are aimed at estimating the angle of arrival of a target and maintaining stable communication link of a guided missile based on a phased array radar in realistic multipath environments. The difficulty in angle estimation of a low altitude target over the sea comes from highly correlated multipath signal which distorts wavefront of the target signal at the antenna face. This problem also appears in the form of intersymbol interference when a multifunction radar system establishes communication link for missile guidance. We shall, therefore, place more emphasis on these problems and aim at proposing the solutions to the problems. In the first part, wave propagation in the atmosphere is presented and analyzed to understand atmospheric effects in angle estimation. Regarding radar problem, the atmospheric conditions cause electromagnetic wave bending, thereby introducing erroneous target position measurement. So it is critical to consider the atmospheric effects to correct the erroneous results. The normal and anomalous propagation conditions are considered and those effects on the a...