Short-Range SAR Imaging From GHz to THz Waves

Synthetic aperture radar (SAR) is a well-known imaging technique and most commonly used up to the microwave frequency spectrum (below 30 GHz) which provides spatial resolution in the sub-m range. To enhance the resolution, higher frequency spectra such as millimeter-wave (mmWave) and terahertz (THz) regions are being investigated. The mmWave and THz spectral ranges extend the SAR applications to non-destructive testing (NDT), material characterization, and sub-mm resolution imaging. However, the higher frequency spectrum suffers from higher path loss and potentially higher atmospheric absorption that limits the propagation distance. Nevertheless, the mmWave/THz spectrum is suitable for short-range applications such as indoor room profiling. From theoretical analysis, it can be summarized that the higher frequency spectrum provides better resolution but a comparative study on the impact on the image quality of the frequency spectrum ranging from GHz to THz has not been presented. Besides, as of the hardware complexity of the THz devices, the optimum range of the spectrum is always under investigation. The optimum range is defined where no strong improvements in the image quality are achievable with further increases in the frequency spectrum. Therefore, this paper presents an overview of electronics-based imaging using the SAR technique for the frequency spectrum ranging from GHz to THz with the focus on NDT and high-resolution imaging. Seven frequency bands: 5-10 GHz, 68-92 GHz, 75-110 GHz, 0.122-0.168 THz, 0.22-0.33 THz, 0.325-0.5 THz, and 0.85-1.1 THz are selected for a comparative analysis. The results are presented for 2D and 3D imaging using the backprojection algorithm. Additionally, state-of-the-art imaging based on SAR technique with electronics transceiver modules has only been demonstrated up to the sub-0.75 THz, whereas in this paper the spectrum up to 1.1 THz has been addressed