Design and characterization of sideband-separating SIS mixer RF hybrids for the Band 3 receiver (84-116 GHz)

The Band3 ALMA front end receiver incorporates sideband-separating (2SB) superconductor-insulator-superconductor (SIS) RF hybrid assemblies to achieve low noise temperatures. The 2SB RF hybrid assembly consists of a feedhorn to direct the RF signals, RF and IF quadrature hybrids for separating the USB and LSB signals, and two SIS mixers to down convert the 100 GHz RF signals to 4-8 GHz IF signals. These assemblies require careful matching of the phase and amplitude of the signals in the USB and LSB pathways to minimize receiver noise. The individual components undergo careful characterization and tests to build suitable 2SB RF hybrids assemblies.