Abstract
A quasi-optical mixer containing two Nb/Al/AlOx/Nb superconducting tunnel junctions integrated into a NbTiN/SiO2/Al microstrip line is studied experimentally in the 800–1000 GHz frequency range. The mixer is developed as an optional front end of the heterodyne receiver operating in frequency band 3 or 4 and incorporated into the HIFI module of the Herschel space-borne telescope. The double-dipole antenna of the mixer is made of NbTiN and Al films; the quarter-wavelength reflector, of a Nb film. The mixer is optimized for the IF band of 4–8 GHz. The double-sideband noise temperature TRX measured at 935 GHz is 250 K at a mixer temperature of 2 K and an IF of 1.5 GHz. Within 850–1000 GHz, TRX remains below 350 K. The antenna pattern is symmetrical with a sidelobe level below −16 dB.
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