Two types of double confocal waveguide $TE_{06}<^>{anti} $ -mode input couplers operating at 140 and 220 GHz are theoretically and experimentally investigated in this article, respectively. The 140 GHz input coupler is based on a power division network structure, while the 220 GHz input coupler is based on a coaxial resonant cavity structure. The field pattern of these two input couplers are analyzed and discussed. The prototypes were fabricated and tested. Back-to-back transmission experimental results agree well with the results of the theoretical simulations. The experimental results show that the 3 dB bandwidth of the power division input coupler at 140 GHz is about 9 GHz and the maximum transmission is -1.4 dB. The 3 dB bandwidth of the coaxial cavity input coupler at 220 GHz is about 3.5 GHz and the maximum transmission is -0.9 dB. It means that a wider bandwidth can be obtained from the power division input coupler, while a higher conversion efficiency can be obtained from\unboldmath the coaxial cavity input coupler. The proposed methodology can be applied to the design of an arbitrary $TE_{0n}<^>{anti} $ (n >= 2) mode input coupler for a double confocal structure gyro-amplifier.

Couplers; Couplings; Bandwidth; Optical waveguides; Apertures; Periodic structures; Waveguide theory; Converter; coupler; double confocal gyro-amplifier; mode purity; terahertz

University of Electronic Science and Technology of China