Prediction of cold-test and hot-test characteristics of a high efficiency linear C-band helix TWT using HFSS, CTLSS, Christine 1-D/3-D

A C-band helix traveling-wave tube (TWT) was modeled using HFSS/CTLSS (3-D electromagnetic codes) to predict the dispersion and impedance characteristics of different sections of the device. This particular TWT consists of two RF sections separated by a sever. As can be seen the input section has distributed loss along the entire length, with a tip loss in the middle; whereas the output section has distributed loss in part of the circuit, with no loss toward the end. The input section has a uniform pitch, whereas the output section has a velocity tapering with a reduction in pitch at the end to improve efficiency. This device operates in the linear region yet producing the desired RF power.