SAR scattering and imaging with focusing by an extended target modeL

Abstract

SAR is a complex system that integrates two major parts: data collector and image formatter [1-2]. In the phase of data collection, radar transmits electromagnetic waves toward the target and receives the scattered waves. The transmitted signal can be modulated into certain types, commonly linearly frequency modulated with pulse or continuous waveform. The process involves signal transmission from generator, through various types of guided device, to antenna, by which the signal is radiated into free space, and then undergoes propagation. The measured scattered signal been made in bistatic or monostatic configurations is essentially in time-frequency (delay time - Doppler frequency) domain. The role of image formatter is then to map the time-frequency data into spatial domain where the targets are located. The mapping from the data domain to image domain, and eventually, into target or object domain must minimize both geometric and radiometric distortions. Essentially, two models that define the SAR operational process: physical model and system model. This paper concentrates on the physical process of a SAR system from wave scattering to imaging. System simulation based on the stationary (frequency modulation continuous wave) FMCW is developed and implemented for both point target and extended target. To further validate the simulation and thus our physical understanding of the imaging chain, measurements at aniconic chamber with two mental spheres and two dielectric spheres displaced with varying spacing were conducted. Good agreement between the simulated by extend target model and real measured SAR images is obtained.