Gap Waveguide-Based MMIC Packaging Solutions for Compact RF Front-End Modules at 100 GHz

Journal article, 2025

This paper presents two innovative packaging techniques for Monolithic Microwave Integrated Circuits (MMICs) designed for multilayer waveguide-based antennas operating near 100 GHz. The first technique involves a transition from a high-permittivity Gallium Arsenide (GaAs) MMIC to a rectangular waveguide using conventional bondwires as the coupling structure within the W-band. This approach enables seamless integration of any off-the-shelf RF chip into waveguide antenna modules without modifying the ground-signal-ground (GSG) pads or adding passive transition substrates. An electromagnetic bandgap (EBG) structure, implemented using metallic pins, effectively suppresses unwanted field propagation. Measurements of a back-to-back (B2B) prototype indicate a reflection coefficient below -10 dB and an average insertion loss of 0.12 dB for a single transition across a bandwidth from 90 to 97 GHz (10.5% relative bandwidth). The second technique introduces a contactless vertical transition from a high-permittivity Alumina (Al2O3) based microstrip line to a waveguide, targeting F-band applications. This proposed concept employs a patch-shaped probe placed on the substrate to couple electromagnetic waves to an H-shaped waveguide aperture positioned above the probe. Experimental results demonstrate a reflection coefficient below -10 dB and an average insertion loss of 0.17 dB over a frequency range of 102 to 120 GHz (15.3% relative bandwidth). In addition, the impact of manufacturing and assembly tolerances on the performance of both transitions is analyzed.