Micromachined Low-Loss Transition from Waveguide-to-Microstrip Line for Large MMIC Integration and Packaging at 250 GHz

Paper in proceeding, 2026

This paper presents two novel transitions; a vertical transition and an inline transition between a rectangular waveguide (WG) and a microstrip line placed in a large substrate. The transitions are suitable to integrate MMICs of arbitrary size. An electromagnetic bandgap (EBG) surface is placed over the transition and the microstrip line to facilitate the coupling of electromagnetic energy from the waveguide to the microstrip line, and to suppress the unwanted waveguide modes. Considering the requirement of fabrication accuracy at sub millimeter-wave (sub-mmWave) frequency the pins constituting a perfect magnetic conductor (PMC) were fabricated by using SUEX dry film photoresist (DFR). A 50 μm thin quartz substrate was also fabricated to pattern the microstrip line with high fabrication accuracy. The vertical transition uses an extra section of E-plane waveguide split blocks for connecting the waveguide section to the flange, and the measured back-to-back transition works over the frequency band of 220-285 GHz (fractional bandwidth of 26%) with a minimum return loss of -12 dB and insertion loss of ~0.9 dB to 1.05 dB per transition. The inline transition uses metal blocks split in the H-plane and introduces some additional leakage loss to the measured insertion loss. The designed transition works over the frequency band of 220-310 GHz with a minimum return loss of -10 dB and insertion loss of ~0.9 dB to 1.2 dB per transition after calibrating out the loss of the metal block.