To address the limitations of conventional radar systems in complex terrains, this paper focuses on two critical challenges. The first challenge is that traditional Synthetic Aperture Radar (SAR) inherently struggles with persistent monitoring due to discontinuous observation patterns and rigid imaging geometries. The second challenge is that fixed phased-array radars lack dynamic adaptability to irregular terrain surfaces despite their beam steering capability. To overcome these constraints, we propose a distributed phased-array radar system using collaborative Unmanned Aerial Vehicle (UAV) swarms. By deploying Frequency-Modulated Continuous Wave Multiple-Input Multiple-Output (FMCW-MIMO) radar modules on autonomous UAVs, the system constructs a reconfigurable virtual array that enables adaptive 3D aperture synthesis. The core innovation lies in the synergistic integration of motion compensation algorithms and distributed synchronization mechanisms, which resolves the inherent conflict between platform mobility and observation stability in conventional radar architectures. Experimental validation confirms enhanced performance in complex terrains, achieving superior angular resolution and coverage efficiency compared to fixed-phased arrays.