Broadband Microstrip-to-Waveguide Inline Transition Using Vivaldi Antenna Excitation

In MMW and THz bands, the transition from the microstrip line to the waveguide is of great significance for packaging integrated circuits in rectangular waveguides. This study presents a novel technique for crafting a broadband microstrip-to-waveguide inline transition using Vivaldi antenna excitation for MMW and THz applications. A tapered-slot converter is employed to achieve wideband mode conversion and impedance matching between the slotline and the open-ended waveguide without the additional quarter-wavelength shorted plane. Moreover, the transition from the microstrip line to slotline is achieved through direct electromagnetic coupling across the quartz substrate. Using the proposed approach, a 0.2-THz inline transition from the microstrip line to the rectangular waveguide is designed and simulated as an example. Promisingly, the transition yields a return loss of better than 15 dB in the frequency range of 170-260 GHz (41.8% bandwidth) with a low insertion loss ranging from 0.6-1.1 dB.