A novel 94-GHz MHEMT resistive mixer using a micromachined ring coupler

In this letter, we present a high performance 94-GHz millimeter-wave monolithic integrated circuit resistive mixer using a 70-nm metamorphic high electron mobility transistor (MHEMT) and micromachined ring coupler. A novel three-dimensional structure of a resistive mixer was proposed in this work, and the ring coupler with the surface micromachined dielectric-supported air-gap microstrip line structure was used for high local oscillator/radio frequency (LO-RF) isolation. Also, the LO-RF isolation was optimized through the simulation. The fabricated mixer has excellent LO-RF isolation, greater than 29 dB, in 2-GHz bandwidth of 93-95 GHz. The good conversion loss of 8.9 dB was measured at 94 GHz. To our knowledge, compared to previously reported W-band mixers, the proposed MHEMT-based resistive mixer using a micromachined ring coupler has shown superior LO-RF isolation and conversion loss.