Abstract: Aiming at the problems that traditional radio frequency (RF) microassembly systems are large in size and difficult to be applied to small platform payloads, this paper studies an RF microsystem technology based on fan-out wafer-level packaging (FOWLP). It focuses on analyzing the microwave characteristics of the fan-out packaging with a 2-layer polyimide/2-layer metal structure, and integrates multiple functional MMIC chips including filters, amplifiers and power ICs into a single RF system-in-package chip. Simulation research is carried out on the microwave characteristics of the redistribution layers for RF-chip interconnection and chip-to-solder-ball connection in the RF system-in-package. On this basis, a C-band RF transceiver microsystem chip is successfully fabricated, which provides a technical reference for the future design and application of FOWLP technology in RF microsystems. The actual test results show that the performance of the chip is basically consistent with that of the traditional microassembly scheme, and the miniaturization of the RF microassembly system is effectively realized. Through batch production tests and practical product applications, its consistency and reliability are guaranteed, which fully verifies the feasibility of this process technology in the design and manufacture of RF microsystem chips.