A SINGLE-CHIP BALANCED SIS MIXER FOR 200-300 GHz

The balanced mixer is fabricated on a 2 x 1 mm quartz substrate which contains an RF quadrature hybrid and two SIS mixers. These components are realized in capacitively-loaded coplanar waveguide, which minimizes stray coupling between adjacent components and coupling to undesired modes in the thick quartz substrate. Signal and LO waveguides are coupled to separate ports of the main substrate via suspended striplines. The mixers were fabricated using the UVA Nb/Al-oxide /Nb process. Over the 225-300 GHz band, the mixer noise temperature was 37-48 K and the overall receiver noise temperature was 46-78 K DSB, both referred to outside the cryostat. The LO-to-RF isolation was >12 dB, which we hope to improve by reducing leakage of power under the substrate between the LO and signal ports.