Demonstration of a Wideband and Compact Input-Output Coupling Structure for Subterahertz Sheet-Beam Traveling Wave Amplifiers

A novel methodology for the beam-wave division/combination in a sheet beam traveling wave amplifier (SB-TWT) is proposed. The design, microfabrication, and measurement of an H-band (220-325 GHz) input-output coupling structures, which originates from an E-plane Riblet coupler with one shorted port, are presented in this article. To experimentally validate the proposed methodology, the designed input-output coupling structure was manufactured by using nanocomputer numerical control milling and measured by using a vector network analyzer. A 3-dB transmission bandwidth of ∼94.0 GHz (231.0-325.0 GHz, 33.8% fractional bandwidth) was measured, over which the measured reflection and isolation coefficients were smaller than -15.3 dB and -11.6 dB, respectively. Compared with other previously reported input-output coupling structures for SB-TWTs, this structure is highlighted by its superior comprehensive performance, including compact geometry, insensitive to the manufacturing tolerance, and good electrical performance over a wide frequency bandwidth, which makes it especially applicable in the terahertz-band operation.