A Terahertz-Band Rectangular TE10 to Circular TE01 Mode Converter

The design, fabrication, and experimental measurement of a broadband and compact TE ^{\Box }_{{10}} -TE ^{\circ }_{{01}} (symbols \Box ^{^{^{}}} and \circ represent the rectangular and circular waveguides, respectively) mode converter is presented in this article. The proposed mode converter consists of three components, including a TE ^{\Box }_{{10}} -TE ^{\Box }_{{20}} mode converter based on a two-way H-T junction power divider, a TE ^{\Box }_{{20}} -TE ^{+}_{{22}} mode converter with variable cross-shaped waveguide, and a TE ^{+}_{{22}} -TE ^{\circ }_{{01}} mode converter. Two distinct design schemes have been employed for the first part of the TE ^{\Box }_{{10}} -TE ^{\circ }_{{01}} mode converter, which are based on two-way H-T junction power dividers with a path difference of odd times half-waveguide wavelength (Scheme 1) and a 180° phase shifter (Scheme 2), respectively. This mode converter is highlighted by the significant advantage of high conversion efficiency over a wide bandwidth with a relatively easy-to-fabricate structure, which is evidenced by the measurement of two identical back-to-back joined mode converters based on Scheme 1. Measurement results matched with simulation ones within reasonable accuracy, which predicted that a 1-dB transmission bandwidth of ~56.7 GHz was obtained. Meanwhile, the reflection coefficient {S} _{{11}} was below −13.2 dB over that bandwidth.