X-Band circular TM02-mode launcher realized by monolithic metal 3D printing

Higher power microwave sources tend to produce circularly symmetric modes utilizing over-moded circular waveguides. Recent advances in such microwave tubes, the TM02 output mode, have been used for its high-power handling. However, there are currently no TM02 mode launchers to characterize waveguide components operating with the TM02 mode. Thus, this paper investigates a TM02 circular waveguide mode launcher from a standard rectangular waveguide input, allowing for interfacing to standard equipment such as a Vector Network Analyzer for measurement. The mode launcher is realized using a metal 3D printing fabrication technique in one whole piece without the need for waveguide flange interfacing or conductive gaskets. The use of metal additive manufacturing allows the monolithic realization of the waveguide component, reducing potential RF losses resulting from waveguide misalignment, flange interfacing losses, or even RF leakage between seams of interconnected parts. The result is a one-piece part fabrication of the TM02 circular waveguide mode launcher, achieving 93.32% efficiency in design. Thus, there is now a means to measure the RF characteristics of the highly over-moded TM02 circular waveguide components using standard equipment.