A Wideband Contactless and Bondwire-Free MMIC to Waveguide Transition

A contactless transition from a high-permittivity microstrip line (€
_r
= 9.9) to an air-filled waveguide (WG) has been impedance-matched over a large simulated relative bandwidth of 38% (W-band, 75-110 GHz). The transition couples the electromagnetic fields directly from the Monolithic Microwave Integrated Circuit (MMIC's) microstrip line via an Substrate Integrated Waveguide and an off-chip stub section to a ridge WG section. The novel structure is low loss and suits pick-and-place assembly techniques of mm-wave MMICs inside metal WGs. The design process is detailed and manufacturing tolerances of the alumina prototype printed circuit board are discussed. The measured back-to-back structure retains an appreciable insertion loss smaller than 0.8 dB for a single transition and a fractional bandwidth of 28% (72-95 GHz) over which the return loss is greater than 10 dB.