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.
Initial results are presented for a 200-300 GHz SIS mixer/preamplifier with an IF bandwidth of 8 GHz. The mixer uses Nb/Al-oxide/Nb tunnel junctions in a circuit with low IF capacitance and inductance. The mixer block mounts directly on the body of a three-stage 4-12 GHz preamplifier which uses discrete InP HFET devices. Mixer bias is provided through the input circuit of the preamplifier. At a LO frequency of 230 GHz, the measured mixer-preamp gain is 30-35 dB, and the DSB receiver noise temperature is 45-57 K across the whole IF band. The preamp alone has 40 dB of gain, and dissipates 7.7 mW. With four amplifiers required in each ALMA cartridge, there is concern that the cooling capacity currently planned for ALMA receivers will be marginal. This mixer/preamplifier has demonstrated that an IF bandwidth of 8 GHz is indeed achievable for ALMA Band 6.
The Atacama Large Millimeter/submillimeter Array(ALMA) Band 1 receiver covers the 35-50 GHz frequency band. Development of prototype receivers, including the key components and subsystems has been completed and two sets of prototype receivers were fully tested. We will provide an overview of the ALMA Band 1 science goals, and its requirements and design for use on the ALMA. The receiver development status will also be discussed and the infrastructure, integration, evaluation of fully-assembled band 1 receiver system will be covered. Finally, a discussion of the technical and management challenges encountered will be presented.
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