Orthogonally coded array for high-speed synthetic aperture radar (SAR) imaging

Abstract

Synthetic aperture radar (SAR) imaging, for nondestructive testing (NDT) purposes, has been applied to a wide range of applications. Within the SAR family, many different imaging systems have been designed and developed to optimize the tradeoffs between image quality, resolution, image production speed, and system hardware complexity. For certain imaging applications, in which weakly scattering targets are of interest, image noise may distort or hide important and desirous features. For such applications, image production speed may be sacrificed in order to achieve the necessary image quality through longer imaging data collection time and averaging. This work implements a method with which an improved tradeoff between image signal-to-noise ratio (SNR) and imaging data collection time is achieved by simultaneously transmitting and receiving from many antennas in an imaging array. In this approach, the transmitted signals are encoded with unique, orthogonal codes, and the received signals are subsequently decoded using the knowledge of the transmitted codes associated with each antenna. Consequently, a new synthetic aperture radar (SAR) imaging system was designed to illustrate the implementation of this approach. The RF system and antenna designs, and system control were specifically implemented for this purpose. The improvement in image SNR was investigated by simulating the system characteristics, as well as measurement of point and distributed targets using the implemented SAR imaging system. The improvement in image SNR was shown by both simulation and measurement to be equal to the length of the codes being transmitted. Additionally, due to the simultaneous transmission and collection of imaging data from many antennas, the improved image SNR is achieved without a proportional increase in data collection time.