As the Atacama Large Millimeter/submillimeter Array (ALMA) nears completion, 73 dual-polarization receivers have been delivered for each of Bands 3 (84-116 GHz) and 6 (211-275 GHz). The receivers use sideband-separating superconducting Nb/Al-AlOx/Nb tunnel-junction (SIS) mixers, developed for ALMA to suppress atmospheric noise in the image band. The mixers were designed taking into account dynamic range, input return loss, and signal-to-image conversion (which can be significant in SIS mixers). Typical SSB receiver noise temperatures in Bands 3 and 6 are 30 and 60 K, respectively, and the image rejection is typically 15 dB.

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Fig. 1. Phasing type of sideband-separating mixer as used in the ALMA Band-3 and -6 SIS receivers. Fig. 2. For a typical Band-6 SIS receiver, contours of (a) mixer gain dB (solid orange lines) and (b) receiver noise temperature (solid blue lines), plotted on a Smith chart of the RF source impedance normalized to the optimum source impedance R opt . The gray contours are the IF output resistance of the mixer normalized to R opt : solid gray lines indicate positive output resistance and dashed gray lines indicate negative output resistance. The squiggly gray line indicates the transition from positive to negative output resistance. The dashed gray circle at |ȡ| = 0.4 indicates the desirable operating region.Abstract -As ALMA nears completion, 73 dual-polarization receivers have been delivered for each of Bands 3 (84-116 GHz) and 6 (211-275 GHz). The receivers use sideband-separating superconducting tunnel-junction (SIS) mixers, developed for ALMA to suppress atmospheric noise in the image band. The mixers were designed taking into account input return loss, dynamic range and signal-to-image conversion (which can degrade the image rejection). Results are given for typical production receivers.

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