(A) study on the performance optimization in high resolution active phased array SAR system

Abstract

Modern synthetic aperture radar system requires a variety of operational modes based on the mission requirements. An active phased array synthetic aperture radar (SAR) system needs to synthesize various antenna patterns to meet the system performance measures such as the range-to-ambiguity ratio (RAR), the noise equivalent sigma zero (NESZ), the swath width and the radiometric accuracy (RA). And also to achieve high resolution impulse response function (IRF), the frequency modulation linearity of a wideband linear frequency modulated waveform is one of the critical requirements in the synthetic aperture radar. In this dissertation, we focus on two aspects among various design problems of the SAR system. One is SAR instrument error compensation and the other is antenna mask design and its pattern synthesis. First, in order to compensate for IRF degradation effect due to the nonlinear characteristic induced from the SAR hardware, the nonlinear characteristic of a SAR instrument is modeled as a polynomial for amplitude and phase error consisting of linear, quadratic and random components, respectively. We propose the waveform compensation method using the system predistortion technique. This method emphasizes on the phase coefficients extraction based on the measurement and analysis of the changing rates of the period of beat frequencies at a specific section within the transmit pulse width. By extracting the amplitude and phase errors from the SAR instrument, the nonlinear effect has been compensated. As a result, IRF is improved and the compensation method is experimentally verified. Second, the primary contribution of this study is the design guidelines for SAR antenna mask based on the SAR performance measures have been presented to help effectively synthesize the various antenna patterns. We also present the quantative equations of the antenna mask template for the mainlobe and sidelobes from the definition of the NESZ, swath width and RAR. The si...