Tests of a 105 Ghz prototype diplexer-combiner based on square corrugated waveguide

Controllable power combination and distribution of multiple sources into multiple transmission lines may increase efficiency and flexibility of ECRH systems. In this work a narrow band diplexer-combiner is presented: it allows fast independent switching of power from two different gyrotrons in two transmission lines. It is based on a resonator made using suitable lengths of square corrugated waveguides (SCW) as beam splitters/combiners. A 105 GHz prototype was installed and tested in a low power configuration. Three SCW 2.5 m long with four mirrors are used to form two nested resonator loops. Two outputs are available and, depending on frequency, the desired amount of output power can be directed in either. Under ideal conditions, a worst-case 98%-2% power split would be achievable. Beam patterns were measured at the output of the first SCW in order to check similarity with the input beam and alignment. Frequency sweeps were made in order to guarantee that the resonant circuit was working properly. Finally, absolute power measurements were made with a quasi-optical bolometer to verify the simulations. Results of all tests are presented and discussed in this work, together with a feasibility study for insertion of the device in an existing ECRH transmission line.