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.