A Study on Drone-borne Multistatic Synthetic Aperture Radar Configuration and Signal Processing

Abstract

Drone-borne synthetic aperture radar (D-SAR) has been attracting significant attention owing to its cost-effectiveness compared to airborne and space-borne synthetic aperture radar (SAR), as well as its ease of adapting to changes in observation scenarios. Thanks to the advancements in drone swarm control techniques, it has become possible to mount SAR modules on multiple drones, allows for simultaneous earth surface and target observations. Furthermore, by separating the transmitters and receivers, research on bistatic and multistatic SAR systems has become feasible, allowing for these SAR systems to serve as test-beds for airborne and space-borne multistatic SAR system. However, drone platforms have limitations due to their lower maximum allowable payload compared to other heavy platforms, which prevent them from carrying complex and bulky hardware. Additionally, they are constrained by battery limitations, preventing them from using power-consuming hardware. For these reasons, D-SAR system primarily employs frequency-modulated continuous wave (FMCW) radar modules to lightweight and lower power consumption of the radar system. Despite the adoption of FMCW radar, SAR image quality degradation, such as range resolution, can arise, and the use of FMCW radar systems necessitates different signal processing techniques compared to traditional pulse-based SAR image signal processing. Therefore, new technologies are required to address these challenges. In this dissertation, considering the challenges associated with D-SAR system, the design of bistatic and multistatic SAR configurations, signal processing to enhance SAR image quality, and bistatic D-SAR configuration design for digital elevation model (DEM) were proposed. First, the SAR system performance parameters were analyzed in a D-SAR environment to confirm the suitability of the designed D-SAR system and operational scenario. Second, a new perspective and signal processing method were proposed to apply the range resolution improvement (RRI) technique, utilizing the cross-track interferometry, to FMCW radar, resulting in improved range resolution of D-SAR images. Third, a bistatic SAR configuration design method and signal processing method were proposed to enable the formation of D-SAR images in the case of specular-reflection bistatic SAR geometry, a capability previously considered nearly impossible in existing SAR studies. Fourth, a multistatic drone-borne SAR scenario was designed, introducing azimuth resolution improvement techniques and combining them with RRI technique to propose a two-dimensional resolution improvement using design of bistatic D-SAR configuration and signal processing. Fifth, a study, covering bistatic FMCW radar synchronization using an external control module and reconstruction method of radar signal corrupted by the asynchronization were introduced. Finally, bistatic FMCW D-SAR configurations to generate appropriate DEM were analyzed and the challenges, associated with it, were presented. All of the studies have been validated for their effectiveness through simulations or real experiments.