Design and Millimeter-Wave Measurement of a Wideband Power Coupling Structure for Sheet Electron Beam Devices

Two power coupling structures based on a Y-type branch waveguide (YTBW) coupler for sheet electron beam devices are presented in this paper. The YTBW coupler is a good choice for the power coupling due to its broad bandwidth property and compact configuration. However, according to the previous studies, it is difficult for a YTBW coupler to obtain good isolation, small port reflection and, meanwhile, high transmission in a broad frequency band. To address this issue, the following two approaches were proposed: 1) introducing multiple branch slots between branch waveguide 1 and branch waveguide 3 of the YTBW coupler to cancel out the electromagnetic (EM) wave propagating toward the isolation port and 2) enlarging branch waveguide 1 at the junction of the three branch waveguides to achieve a port impedance matching and guide the EM wave to propagate to the port connecting with the slow wave structure. The measured results demonstrated that the bandwidth of port reflection lower than 12.5 dB, isolation coefficient smaller than 12.0 dB, and meanwhile, the transmission higher than 1.0 dB, was 13.5 GHz (50.0-63.5 GHz), corresponding to a fractional bandwidth of 23.8%.