Transmission Line Theory and Thermal Analysis of Coaxial Coupler for TWTs

This paper presents the transmission line analysis, thermal and structural analysis of a multi-section coaxial coupler (MSCC) used in traveling-wave tubes (TWTs) to handle high average power over a wide frequency range. Power transmission through coupler from the device demands very good matching between load and source impedances such that low voltage standing wave ratio (VSWR) is achieved. Modeling of the MSCC for wideband TWTs in commercially software packages takes very long iteration time even in high-end computers. An analytical approach has been developed to model MSCC which takes less iteration time even in ordinary computer. Analytical results have been compared to those obtained from CST microwave studio. Finally, thermal and structural analysis has been carried out to study the thermal aspects for handling high average RF power.