W-band IQ sub-harmonic mixers with low LO power for cryogenic operation in large arrays

This paper presents the design and characterization of W-band IQ sub-harmonic MMIC mixers based on the UMS BES Schottky diode process. The mixers were characterized at 300 K and 20 K physical temperature. They are a key component for the compact heterodyne multi-chip modules to be used in the 16-element Argus focal plane array, which will be deployed at the Green Bank Telescope in late 2014. The RF signal is split in quadrature using a Lange coupler, LO is split in-phase using a Wilkinson divider, and an antiparallel diode pair is used for the design of two sub-harmonically pumped mixer cells. The resulting IF outputs from the two cells are I and Q, which can be combined using an off-chip 90 degree hybrid to obtain LSB and USB. Three mixer designs are fabricated using this topology. A conversion loss between 12 to 18 dB is obtained over 80 to 120 GHz of RF for a fixed IF frequency, and over 10 GHz of IF for a fixed LO frequency. These mixers are designed to operate with low LO power without a significant loss in performance.