Study of H-Band High-Order Overmoded Power Couplers for Sheet Electron Beam Devices

The design of H-band (220-325 GHz) high-order overmoded power couplers for sheet electron beam (SEB) devices is presented in this article. The proposed power coupler was mainly based on the coupling apertures and possessed the functions of both the mode conversion and the beam wave convergence/separation. To compensate for the junction discontinuity and, thus, reduce the port reflection, triangular septa and matching steps were introduced. A rectangular Bragg reflector was used in the SEB tunnel to further improve the performance of the coupler. Two identical rectangular TE₂₀-mode couplers joined back-to-back were fabricated by the nano-computer numerical control (CNC) machining, and the S-parameters were measured by using a vector network analyzer. The measured S-parameters agreed well with the simulated ones that are achieved from the coupler model with measured dimensions when considering the ohmic loss. A 3-dB transmission bandwidth of \sim 56.3 GHz (222.2-278.5 GHz) was measured with a maximum transmission coefficient of -4.4 dB and a port reflection of \sim \!\!-15.0 dB.