D-Band GCPW-to-Waveguide Transition Using Silicon Micromachined Technology for Planar Integrated MMIC and Aperture Antenna

This letter proposes a D-band transversal transition from a ground coplanar waveguide (GCPW) to an air waveguide. Such design is critical to the radio frequency (RF) front end between the monolithic microwave integration circuit (MMIC) and aperture antenna especially in sub-terahertz frequency due to the high loss in dielectric substrate. Silicon micromachined technology, as an advanced packaging technology, not only features a multilayer arrangement similar to the printed circuit board (PCB) technology, but also supports the development of air cavities inside it, such as the rectangular waveguide. Adopting this technology, a WR-6 waveguide with a reduced height of 150 µm is developed within silicon substrates. Moreover, inspired by the classical aperture-coupled antenna, a magnetic coupling structure comprising a short-circuit end and a same-layer coupling aperture are proposed to facilitate the mode transformation from quasi-TEM to TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub>. Benefiting from this structure, the signal from GCPW is effectively transmitted to the waveguide. Measurements of two back-to-back prototypes indicate that the average insertion loss of one proposed transition is 0.355 dB within D band, and the 1 mm-length waveguide induces loss of 0.075 dB, respectively. The transition is with low profile of 400 µm and a wide bandwidth of 42.9%, which is promising for planar sub-terahertz system.