Band-4+5 initial prototype receiver front-end for ALMA2030 wideband sensitivity upgrade
Abstract
The Atacama Large Millimeter/submillimeter Array (ALMA) Band-4+5 receivers are proposed for the upgrade after 2030. The new receiver will cover the RF frequency of the original Band-4 (125–163GHz) and Band-5 (163–211GHz) with continuous frequency tuning over dual polarizations, dual sidebands with instantaneous intermediate frequency (IF) bandwidth up to 16 GHz per sideband and per polarization. The SIS-based receiver scheme is chosen as the baseline design. The niobium-based SIS junctions were fabricated to form mixer chips, and integrated into the mixer blocks with WR-5.44 waveguide 3-dB quadrature hybrid couplers, LO power dividers and 17-dB directional couplers, bias tee, cryogenic IF low-noise amplifiers, and 4-20 GHz coaxial 3-dB quadrature hybrid couplers to form sideband separating down-converters, with the input fed by the ellipsoidal mirror pairs outside the vacuum window, corrugated feedhorn and the orthomode transducer, and the output via stainless steel coaxial cables and the vacuum feedthroughs to form the cold cartridge assembly (CCA). For the warm cartridge assembly, a pair of sideband-separating mixers composed by WR-5.44 waveguide 3-dB quadrature hybrid couplers, subharmonic diode/transistor mixers, and 2–20GHz coaxial 3-dB quadrature hybrid couplers will provide four-channel 16-GHz IF instantaneous bandwidth. To avoid the possible interference between LO and IF signals, considering the possible 16 GHz IF bandwidth over 4–20GHz, the LO fundamental frequency will be chosen in 24–32GHz, followed by an active frequency tripler to form the phase-lock loop with 72 – 96 GHz frequency tuning range. The 72–96GHz signal is then fed into W-band power amplifiers to provide 40mW power to pump the Schottky diode frequency doublers to adequately pump the SIS mixers. The key components with 51.2% relative bandwidth have been developed in-house are (i) Nb SIS mixers, (ii) 3-dB waveguide hybrid couplers with LO divider-coupler, (iii) orthomode transducers, (iv) corrugated horn antenna, (v) optics mirror pairs. Both component and system performance will be reported.