A study on the output beam profile of a ring resonator type diplexer

A ring resonator type diplexer was tested for fast switching device for ECCD system. The ring resonator was composed by circular corrugated waveguides with 63.5 mm diameter. Four in/output ports were separated from the resonator by half mirrors. The resonance frequency and its interval were designed as 170 GHz and 460 MHz, respectively. The mock-up diplexer which utilizes slotted planes with 2 mm period or sapphire disk with 1 mm thickness as half mirrors were examined at using 170 GHz-band low power oscillator. RF beam with 95% of the fundamental mode (LP01 mode) was provided into the input port of the diplexer using a mode generator. Beam profiles from output ports were measured and mode contents in output ports were deduced. When the slotted mirrors were utilized, the LP01 mode purity was decreased as 85% at the resonance frequency, 170 GHz. This was because higher order modes were induced by the higher order diffraction beams from the slotted half mirror. On the other hand, mode purity was increased higher than 98% at 170 GHz when sapphire mirrors were utilized.