Abstract: A microwave plasma chemical vapor deposition device for diamond synthesis. A microwave source generates a microwave signal, and a resonant cavity receives a plurality of process gases. The microwave signal is spread in a first mode at a first waveguide. A mode conversion antenna converts the first mode of the microwave signal into a second mode that is spread at a second waveguide. A coupling conversion cavity receives and transmits the microwave signal in the second mode to the mode conversion antenna thereby converting the second mode of the microwave signal into a third mode. A medium viewport receives the microwave signal in the third mode and transmits to the resonant cavity which enables the microwave signal to excite and discharge the process gases to form spherical plasma, carbon containing groups and atomic hydrogen thereby depositing a diamond film on a seed.