Design and Measurement of Terahertz-Band Rectangular TE10 to Circular TEn1/TE0p/TE1q Mode Converters

A novel methodology to perform mode conversion from rectangular fundamental TE₁₀ mode to circular TE $_{n1}$ ( $n $ = 2, 3, $4, \ldots $ )/TE $_{0p}$ ( $p $ = 1, 2, $3, \ldots $ )/TE $_{1q} (q $ = 2, 3, $4, \ldots $ ) modes with similar topologies is presented in this article. The mode converter consists of two sections: a novel H-plane T-junction-based rectangular TE $_{m0}$ ( $m $ = 2, 3, $4, \ldots $ ) mode launcher and a rectangular TE $_{m0}$ -circular TE $_{n1}$ /TE $_{0p}$ /TE $_{1q}$ mode converter. This kind of mode converter possesses good comprehensive performance and is highlighted by three primary advantages: 1) it is flexible to produce various circular TE modes and rectangular TE $_{m\mathrm {0}}$ modes; 2) the mode converter has a relatively simple and easy-to-fabricate geometry, making it especially suitable for the terahertz-band operation; and 3) it possesses a high mode conversion efficiency over a wide bandwidth, which is adequate to satisfy most of the application requirements. The analysis of mode conversion principle, numerical simulations, microfabrication, and experimental measurement of two H-band (220–325 GHz) prototypes are described. Back-to-back measurement results exhibited good agreement with simulation predictions having considered the conductor loss. A 3-dB transmission bandwidth of 56.7 GHz (231.4–288.1 GHz)/42.1 GHz (244.0–286.1 GHz) was experimentally obtained for the ${\mathrm {TE}}^{\square}_{10}-{\mathrm {TE}}_{01}^{\circ}/{\mathrm {TE}}_{31}^{\circ}$ mode converter.