Design and Microwave Measurement of a Broadband Compact Power Coupler for Sheet Beam Traveling Wave Tubes

Novel compact input and output couplers for broadband operation of sheet beam traveling wave tubes are analyzed, designed, and cold tested. Multistage stepped waveguide and cascaded Bragg resonators are proposed and applied to improve the performance and extend the operating bandwidth. Optimized curve-Bragg resonators are studied to correct the phase between the reflector and H-bend waveguide, which bring about a further enhancement of the coupler behavior. HFSS simulations predict a -3 dB transmission bandwidth about 38% and 34% are achieved, respectively, in Ku and Q band. Besides, the large beam tunnel property of this kind of coupler benefit the beam transport of sheet beam devices. Different components as the input and output couplers for Kuand Q-band SB-TWT are manufactured and cold tested. Results of vector network analyzer measurement and simulation present an excellent agreement.