Band-4+5 Receiver Front-End: Idea and Initial Development in East Asia Consortium

We propose an upgrade to the ALMA Wideband Sensitivity Upgrade (WSU) by developing a new receiver with increased RF and IF bandwidth. The new receiver will cover the RF frequency of the original Band-4 and Band-5 with continuous frequency tuning over dual polarizations, dual sidebands with instantaneous intermediate frequency (IF) bandwidth up to 16 GHz per sideband and per polarization. Both the SIS-based receiver and HEMT-based receiver schemes are considered. The SIS-based receiver is considered as the baseline design, a sideband separation downconverter with the input fed by the ellipsoidal mirror pairs, corrugated feedhorn and the orthomode transducer form the cold cartridge assembly (CCA). The niobium-based SIS junctions will be fabricated to form mixer chips, and integrated into the mixer blocks with WR-5.44 waveguide 3-dB quadrature hybrid couplers, cryogenic IF low-noise amplifiers, and 2-20 GHz coaxial 3-dB quadrature hybrid couplers to form sideband separating down-converters. For the HEMT-based receiver scheme, the cryogenic InP HEMT low-noise amplifiers (LNAs) chains cover 125 - 211 GHz operated in 15-K ambient temperature will be the key components, to suppress multiple reflection ripples, cryogenic 2SB mixers are considered. To avoid the possible interference between LO and IF signals, the LO fundamental frequency are chosen in 24 - 32 GHz, followed by a frequency tripler to form the phase-lock loop with 72 - 96 GHz frequency tuning range.