The idea of 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 and Band-5 with continuous frequency tuning over 125 –211 GHz with dual polarizations, dual sidebands capability. The instantaneous intermediate frequency (IF) bandwidth is up to 16 GHz per sideband and per polarization. Both the SIS-based receiver and HEMT-based receiver schemes are considered. For the SIS receiver scheme, the niobium-based SIS junctions will be fabricated to form mixer chips, and integrated into the mixer blocks with broadband waveguide 3-dB quadrature hybrid couplers with LO couplers, cryogenic IF low-noise amplifiers, and 2-20 GHz coaxial 3-dB quadrature hybrid couplers to form sideband separating down-converters. The inputs of the sideband separating down-converters are fed by the ellipsoidal mirror pairs, corrugated feedhorn and the orthomode transducer. For the HEMT-based receiver scheme, using the same optics configuration as the SIS-based receiver, the cryogenic InP HEMT low-noise amplifiers (LNAs) chains cover 125 – 211 GHz operated in 15-K ambient temperature will be the key components of the cold cartridge assembly (CCA). For the warm cartridge assembly, a pair of sideband-separating diode or resistive transistor mixers 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 – 20 GHz, the LO fundamental frequency will be chosen in 24 - 32 GHz, followed by an active frequency tripler to form the phase-lock loop with 72 – 96 GHz frequency tuning range. The key components with 51.2% relative bandwidth to be developed in-house are Nb SIS mixers, RF InP HEMT LNAs, 3-dB waveguide hybrid couplers, orthomode transducers, corrugated horn antenna, and optics mirror pairs.
In pursuit of advancing large array receiver capabilities and enhancing the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT), we have successfully fabricated 230 GHz finline superconductor-insulator-superconductor (SIS) mixers. These mixers are critical for assessing the potential and prospective for the HARP instrument’s upgrade. Unlike the existing HARP’s mixer, we replace the probe antenna with an end-fire unilateral finline as the waveguide to planar circuit transition. This mixer design is expected to operate from about 160–260 GHz (approximately 47% bandwidth), and the mixer chips’ current-voltage (I-V) curves have been characterized, showing promising results with a quality factor (Rsg/Rn) exceeding 9.3. Evaluation of the double-sideband (DSB) receiver noise temperature (Trx) is currently underway. Once successfully characterised, our immediate aim is to scale the mixer to operate at HARP’s frequency range near 345 GHz to achieve similar broad RF bandwidth performance. Ongoing simulations are currently being conducted for the design of the 345 GHz finline mixer. This work marks a crucial step toward enhancing HARP receiver performance with better sensitivity and wider Intermediate Frequency (IF) bandwidth, enabling higher-frequency observations, and expanding the scientific potential of the JCMT and its collaborative partners.
The far infrared instrument SAFARI spectrometer on board the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) provides moderate resolution spectra (R~300) with simultaneous coverage over 34 to 230 μm. With the high sensitivity TES detectors, the SAFARI can reach the sensitivity down to ~7×10-20 W/m2. In order to provide accurate calibration for the TES readout circuit, a calibration source assembly (CSA) is developed to provide a stable and absolute flux radiation to the spectrometer over the whole spectral range. The CSA has a primary function during observations to take periodic reference measurement to correct for drift, subtracting backgrounds, etc from the detector. The CSA is composed of three microlamps and one integrating sphere. The microlamps are made of resistance wires by microlithography to mimic square blackbody sources. By combining an 81K microlamp and a 24K microlamp, a reasonably flat spectrum can be produced at the output of the integrating sphere. The radiation to the transition edge sensor detector pixel is around 1×10-16 W. The integrating sphere can also provide a uniform output to cover the size of SAFARI field of view including the target and sky pixels. In this paper, the CSA design and the prototype results of the microlamp and the integrating sphere are presented.
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