Study on single‐mode transmission in non‐radiative dielectric waveguide

In order to develop millimeter‐wave integrated circuits, low‐loss and compact waveguide devices have been intensively investigated in recent years. Non‐radiative dielectric waveguide (NRD guide) is expected to be a platform for millimeter‐wave and THz‐wave circuits because of its non‐radiative nature. However, conventional NRD guides support and modes simultaneously and mode conversion between these modes often occurs at bends and discontinuities. Therefore, circuit devices have to be carefully designed not to excite unwanted mode. In this paper, we propose a sub‐wavelength grating NRD guide (SWG‐NRD guide) to achieve single‐mode transmission band of mode. SWG structure can easily control dispersion property of transmission modes and cut‐off frequency of mode can be greatly shifted to higher frequency side. The designed SWG‐NRD guide achieves a wide transmission band of 20 GHz with a central frequency of 60 GHz. We also propose a taper waveguide to connect SWG‐NRD guide with the conventional NRD guide with low reflection. Finally, we present the propagation characteristics of the SWG‐NRD guide bend. The proposed SWG‐NRD guide shows high transmission efficiency and overcomes the problems of mode conversion in NRD guides.