Abstract-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.

We propose the design of a dual-anode electron gun, so named due to the presence of an additional electrode, namely, the control anode in the vicinity of the cathode in addition to the ion-barrier anode and the ground anode. We found the potential of the control anode to play an important role in enhancing the life of a space traveling-wave tube. By a telemetric command, one could control the control anode potential with a view to enhancing the cathode current that would otherwise deteriorate with the progress of time. Further, due care was taken in the thermal design by providing a heat shielding of the cathode of the proposed dual-anode gun to ensure that the cathode, which is operated at a lower temperature for a longer cathode life, does not further suffer a decrease in temperatures due to heat dissipation. Furthermore, to compensate for the deterioration of the cathode current with the progress of time, we propose the application of a nominal change in the control anode potential by a telemetric command. The electrostatic and thermal simulations of the proposed dual-anode gun were carried out by the commercial simulation codes EGUN and ANSYS, respectively. The paper presents the effect of heat shield thickness and material property on the cathode temperature as well as the effect of the structural deformation caused by the axial and radial expansion of the cathode on electron beam optics, a demountable dual-anode gun was set up for validating the cathode temperature against simulation.