Design of Balanced Mixers for ALMA Band-10

摘要

Two variants of balanced mixer employing twin-SIS structure are under development for 787–950 GHz frequency range. Easy-to-use Geometry Transformation method for modeling of superconducting microstrips is developed, compared to referenced methods and used for design of the mixers. Lens-antenna mixer is based on cross-slot antenna; it does not need any intervening optics between its lens and sub-reflector of ALMA telescope; simple yet efficient composition of lens-antenna cartridge is suggested. Compact single-chamber balanced waveguide mixer employs two SIS chips and capacitive probe for LO injection; coupling above $-$3 dB and signal loss below $-$20 dB are expected. Need in shifting of resonance frequency of twin-SIS mixer towards top of the frequency band is predicted using Tucker''''s theory in large-signal approximation. ${rm T}_{rm RX}$ considerably below 200 K (DSB) is simulated using high-quality hybrid SIS junction ${rm NbTiN/Nb-AlO}_{rm x}-{rm Nb/Al}$ for ${rm J}_{rm c}=12 {rm kA/cm}^{2}$.