A Terahertz Band TE20□ Mode Input/Output Coupling Structure for Dual-Sheet-Beam Traveling-Wave Tubes

This article presents the design, microfab- rication, and measurement of a terahertz band
${\mathrm {TE}}^{\Box }_{20}$
mode input–output coupling structure for dual-sheet-beam traveling-wave tubes (TWTs). The proposed coupling structure is based on an
$E$
-plane Riblet slot coupler with one shorted port and a
${\mathrm {TE}}^{\Box }_{10}$
–
${\mathrm {TE}}^{\Box }_{20}$
mode converter. Compared to the previously reported high-order mode (HOM) coupling structures, the proposed structure possesses superior electrical and mechanical performance, including better reflection/transmission properties and relatively easy-to-fabricate configuration with features insensitive to fabrication tolerances. For verification, two
$H$
-band (220–325 GHz) identical
${\mathrm {TE}}^{\Box }_{20}$
mode coupling structures joined back-to-back were manufactured and measured. Good agreement between the experimental results and the simulated responses is observed. The fabricated prototype of the coupling structure exhibits good electromagnetic (EM) performance over a bandwidth of 52.1 GHz (243.2–295.3 GHz) with a transmission coefficient better than −1.5 dB and a port reflection lower than −15.0 dB.