Transition of 94-GHz coplanar waveguide to rectangular waveguide on flip-chip bonding compatible substrate

We demonstrate a 94-GHz coplanar waveguide (CPW) to rectangular waveguide transition on high permittivity sapphire substrate. Monolithically fabricated uniplanar transition is composed of the fin-line taper and the open-type CPW to slotline transition that can be fully integrated with the flip-chip bonded monolithic microwave integrated circuits (MMICs) on single rigid sapphire substrate. From an optimized design of a low-loss single-section transition, we fabricate the back-toback transition for the characterization. The measurements show an insertion loss of ∼1.7 dB at 94 GHz from a single-section transition, and the performance is successfully verified from a 94-GHz mixer module assembled with a flip-chip bonded MMIC mixer.