A Fixed-Tuned SIS Mixer with Ultra-Wide-Band IF and Quantum-Limited Sensitivity for ALMA Band 3 (84-116 GHz) Receivers

This paper describes an 84-116 GHz Nb/Al-oxide/Nb SIS mixer with multi-octave IF bandwidth and quantum-limited sensitivity. The mixer can be integrated with a three-stage 4-12 GHz HFET preamplifier or fitted with a coaxial connector for operation with an external isolator and IF amplifier. An 84-116 GHz receiver using the mixer with an integrated 4-12 GHz HFET preamplifier has a double sideband noise temperature of 16-20 K (3 to 4 h</kB) over most of the IF band. Analysis of the mixer-preamp using Tucker=s theory shows good agreement with measurements. The mixer is easy to build and is being used as a building block for the Band 3 sideband-separating receivers for the Atacama Large Millimeter Array (ALMA) ** . With minor modifications, this mixer design can be scaled to other ALMA bands. I INTRODUCTION

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