On the design of coaxial coupler having multi-section short transformer for compact sized power helix travelling wave tubes

Summary form only given. A coaxial coupler, used for the extraction of microwave power from broadband compact power helix traveling wave tubes (TWTs) consists of a multi-section short transformer and a rf window assembly. For such tubes multi-section /spl lambda//4 (/spl lambda/: wavelength) transformers are not feasible and in place multi-section short transformers (section length less than /spl lambda//4) have to be used, whose design is not well established. Also rf power absorption in the window ceramic becomes considerable at X-band and beyond. The tiny size of the ceramic window disc results in a substantial rise of window temperatures and needs be considered. Therefore, the thermal considerations in the design of couplers becomes necessary especially for space TWTs to ensure reliability. This work deals with the development of a design approach for the above miniature couplers. The whole coupler assembly has been considered as a cascade of multi-section transmission line of arbitrary lengths. A helix slow wave structure (SWS) is taken as the load to which one end of the transformer is terminated.