Design and Measurement of Terahertz Broadband Vertically Coupled High-Order TE □ n0 Mode Converters

The theoretical analysis, simulation, fabrication and measurement of a novel TE□10-TE□n0mode converter is described in this paper. In the existing research work, although a significant portion of mode converters have the expansibility to higher-order modes, the performance of the mode converters will deteriorate when the mode index increases. As we know, no mode converters operating higher than TE□70mode have ever been reported. To address this issue, a novel vertically coupled mode converter for converting the TE□10mode to higher-order TE□n0mode is proposed in this article. As examples, the TE□10-TE□80and TE□10-TE□70mode converters are designed. Simulated results show that the 1 dB transmission bandwidths of the TE□10-TE□80and the TE□10-TE□70mode converters are 56.1 GHz (228.7-284.8 GHz) and 50.0 GHz (232.3-282.3 GHz), respectively. Within the operating bandwidth, the reflection coefficientsS11of both mode converters are less than -15 dB and the conversion efficienciesS21of the targeted TE□80mode and TE□70mode are higher than 99% and 92%, respectively. Additionally, two back-to-back connected TE□10-TE□80mode converters are fabricated and measured to verify the design. The measured S-parameters align well with the simulated results and exhibit a flat response, which confirms the feasibility of the proposed mode converter and shows that it can achieve good performance at much higher-order modes.