Design and Measurement of Terahertz-Band Rectangular TE<sub>10</sub> to Circular TE<sub> <i>n</i>1</sub>/TE<sub>0<i>p</i> </sub>/TE<sub>1<i>q</i> </sub> Mode Converters
Guoxiang Shu, Jingcong He, Jiacai Liao, Junchen Ren, Haoxiang Mai, Jujian Lin, Guangxin Lin, Qi Li, Bentian Liu, Guo Liu, Cunjun Ruan, Wenlong He
Abstract
A novel methodology to perform mode conversion from rectangular fundamental TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode to circular TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{n1}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n $ </tex-math></inline-formula> = 2, 3, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4, \ldots $ </tex-math></inline-formula> )/TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{0p}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p $ </tex-math></inline-formula> = 1, 2, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3, \ldots $ </tex-math></inline-formula> )/TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1q} (q $ </tex-math></inline-formula> = 2, 3, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4, \ldots $ </tex-math></inline-formula> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{m0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m $ </tex-math></inline-formula> = 2, 3, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4, \ldots $ </tex-math></inline-formula> ) mode launcher and a rectangular TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{m0}$ </tex-math></inline-formula> -circular TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{n1}$ </tex-math></inline-formula> /TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{0p}$ </tex-math></inline-formula> /TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1q}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{m\mathrm {0}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {TE}}^{\square}_{10}-{\mathrm {TE}}_{01}^{\circ}/{\mathrm {TE}}_{31}^{\circ}$ </tex-math></inline-formula> mode converter.