Design of a Millimeter Wave Mixer for Downconversion

Abstract

Millimeter wave (mmW) frequency bands 105{116 GHz and 217{231 GHz are dedicated to Earth exploration-satellite services, space research, and radio astronomy. These applications demand high-quality mmW front-ends. Inside these front-ends, mixers play a key role in converting the received signals to lower frequencies before amplification and signal processing. In this project, a subharmonically-pumped (SHP) antiparallel-pair Schottky diode mixer working around 110 GHz is presented. A conversion loss of less than 20 dB with a bandwidth of roughly 10 GHz was achieved in simulation. The estimated downconversion loss from upconversion measurements is around 60 dB over 4 GHz. A metal blocks was designed to support the suspended-microstrip on which the diode pair was placed. An attempt was made to design another subharmonic mixer (SHM) around 220 GHz. To increase the LO power delivered to the diode pair, impedance matching at the local oscillator (LO) frequency was achieved with stepped-impedance sections. Implicit space mapping (ISM) technique was used to optimize the matching network.