FMCW SAR System for Near-Distance Imaging Applications—Practical Considerations and Calibrations

A combination of frequency-modulated continuous-wave (FMCW) technology with a synthetic aperture radar (SAR) technique is a highly sought after method, which leads to a compact and cost-effective imaging system, for near-distance target imaging. One of the limiting factors of FMCW radars is that the ramp signal modulates the received signal, which limits the minimum achievable range resolution. In addition, the voltage-controlled oscillator (VCO) adds a certain degree of phase noise and nonlinearity to the transmitted signal that degrades the signal-to-noise ratio, range accuracy, and image resolution. This paper presents a signal processing procedure with system calibration methods to mitigate the effect of deramp, phase noise, and nonlinearity of the VCO on the beat spectrum. Additionally, the effect of phase noise of the received signal on the SAR image resolution in both range and cross-range directions is comprehensively studied. To improve the range accuracy, different calibration methods are proposed. An S-band homodyne FMCW radar system, using off-the-shelf components, is designed for near-distance target imaging using linear and circular SAR techniques. The reconstructed images show the improvement of image quality and accuracy in target position.