Millimeter wave planar transition from plastic rectangular waveguide to 1 mm coax

This paper reports on a planar transition from 1 mm coax to the fundamental mode of a polystyrene rectangular dielectric waveguide (DWG), covering frequencies from 50 GHz to 85 GHz. Two back-to-back transitions connected by a 12 cm piece of waveguide with tapered points were measured, demonstrating an insertion loss between the microstrip line and the dielectric waveguide of about 2 dB, which agrees well with simulated values. The structure consists of a 1 mm coaxial board edge connector feeding a microstrip line on a 4 mil thick liquid crystal polymer (LCP) substrate, followed by a vialess transition from microstrip to slotline patterned on the other side of the substrate. The slotline then tapers out and feeds a tapered DWG that is connected to the LCP board by inserting it into a slit along the center of the waveguide.