Abstract: Enhancing the output power of high-power microwave (HPM) systems remains a central challenge in HPM research. Power synthesis technology serves as a critical method to increase the output power while breaking through the performance improvement of a single high-power microwave source. This paper presents a beat-wave synthesizer based on mode-conversion filters, configured as a dual-channel device. Each channel incorporates a circular-to-rectangular waveguide TM01-TE10 mode converter integrated with sidewall coupling structures and short-circuited waveguide sections to achieve simultaneous mode conversion and beat-wave synthesis. The prototype demonstrates 95% synthesis efficiency with gigawatt-level power handling capacity. Its compact configuration and low manufacturing complexity enable effective mode transition and wave synthesis, offering enhanced feasibility for miniaturized system integration.