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

A novel methodology for the beam-wave division/combination in a sheet beam traveling wave amplifier is proposed. The design, microfabrication, and measurement of H-band (220-325 GHz) input/output coupling structures are presented in this article. This geometry is based on an E-plane Riblet coupler with one shorted port. A rectangular single capacitive step, gradual geometries, and a rectangular septum are introduced to improve electrical performance. To experimentally validate the proposed methodology, the designed input/output coupling structure was manufactured by using nano computer 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), corresponding to a fractional bandwidth of 33.8%, was measured with a maximum transmission coefficient of -2.3 dB. The measured port reflection and isolation coefficients were smaller than -15.3 dB and -11.6 dB within the 3-dB transmission bandwidth, respectively. Compared with other previously reported input/output coupling structures for sheet beam traveling wave amplifiers, this structure has two significant advantages: compact configuration and wide frequency bandwidth, which make it superior and more applicable.