Design of a 3.7 GHz TE10-TE30 mode converter using stepped impedance transformer for CW applications

This paper presents the design and simulation of a novel TE10 to TE30 mode converter operating at 3.7 GHz and is subjected to high RF power of 500 kW in Continuous Wave (CW) regime. The design incorporates a stepped impedance transformer as opposed to the conventional capacitive button to improve the return loss and power handling capacity of the converter. A rigorous RF, breakdown and multiphysics analysis including thermal, fluid dynamics and stress physics is performed on the mode converter to ascertain its viability and usefulness as a power dividing network in the Passive Active Multijunction launcher for Lower Hybrid Current Drive systems of tokamaks. The proposed mode converter exhibits a return loss of similar to 50 dB, mode conversion efficiency of similar to 97% and a peak E-field of 685 kV/m is obtained as compared to that of 4.2 MV/m obtained in the conventional mode converter. Thus, the power handling capacity of the proposed mode converter design is found to be 97.3% higher than the conventional mode converter.