Design of a 240GHz on-chip dual-polarization receiver for SIS mixer arrays
Abstract:
We report the design of a compact dual-polarization on-chip superconductor–insulator–superconductor receiver for array applications. The planar-circuit receiver chip is comprised of the entire radio frequency (RF) signal processing chain with three main circuit components alongside some auxiliary circuits: (1) a polarization splitting 4-probe orthomode transducer (OMT) that couples the RF and local oscillator signal from free space to the chip via a drilled feedhorn; (2) two hybrids that recombine the power of each polarization from the two sets of orthogonal OMT probes; and (3) twin-junction Nb/AlOx/Nb mixers that downconvert the recombined signals to the intermediate frequency. We ensure that the four side walls of each pixel are free from obscuration, using only the top and bottom of the pixel for various connections. Consequently, the design is extendable to a large format array. In this paper, we present the detailed design of the on-chip receiver, including extensive heterodyne simulations and its potential extension into a large format array.Design of a 350 GHz circular waveguide superconductor-insulator-superconductor mixer for array applications
Abstract:
We present the design of a superconductor-insulatorsuperconductor (SIS) mixer fed with a 2-probe antenna mounted in a circular waveguide, hence avoiding the need for a rectangular waveguide that is often difficult to machine at high millimetre and sub-millimetre frequencies. The mixer is designed to operate from 275–375 GHz, covering a similar frequency range to the HARP-B receiver of the James Clerk Maxwell Telescope. Each antenna probe is connected to a separate but identical mixer circuit comprising three SIS junctions connected in series to reduce the parasitic capacitance, and the relevant tuning circuits and RF chokes. The down-converted IF power at the output of each mixer branch is expected to be combined using either a microwave Wilkinson power combiner or a 180◦ hybrid, to recover the full signal strength. In this paper, we present in the detail the electromagnetic simulations of each RF component making up the mixer chip, as well as the performance of the entire 2-probe mixer including the RF and IF performance predicted using SuperMix, a software package developed based on Tucker’s theory of quantum mixing. Finally, we show how such circular waveguide SIS mixers can be easily populated onto a simple split-block to form a 16-pixel array.Design of an on-chip integrated 230 GHz dual-polarization balanced SIS receiver for multi-pixel array applications
Abstract:
We report the design of a 230 GHz dual-polarization (2-pol) balanced Superconductor-Insulator-Superconductor (SIS) receiver that can be easily extended for large array applications. We achieve this by integrating all of the required radio frequency (RF) and local oscillator (LO) components on-chip using planar superconducting circuit technology, therefore simplifying the architecture of the receiver block substantially. One major feature of our design is the planar LO injection scheme, which couples the LO with a single on-chip antenna and distributes the LO power via a series of microstrip couplers to the balanced mixers of each polarization of each pixel. In this paper, we describe in detail the design and layout of the individual planar circuit components of our receiver, as well as how they are integrated to form a full receiver. We then conclude the paper with the design of a 2-pixel array demonstrator, illustrating how the balanced SIS mixer and the LO distribution network can be extended to form an even larger array.A closed-cycle miniature dilution refrigerator for a fast-cooldown 100 MK detector wafer test cryostat
Abstract:
The forthcoming generation of cosmic microwave background polarization observatories is developing large format detector arrays which will operate at 100 mK. Given the volume of detector wafers that will be required, fast-cooldown 100 mK test cryostats are increasingly needed. A miniature dilution refrigerator (MDR) has been developed for this purpose and is reported. The MDR is precooled by a doublestage 3He–4He Chase Research Cryogenics sorption refrigerator. The test cryostat based on this MDR will enable fast cooldown to 100 mK to support rapid feedback testing of detector wafers fabricated for the Simons Observatory. The MDR has been designed to provide a 100 mK stage to be retrocompatible with existing CRC10 sorption coolers, reducing the base temperature from 250 mK for the new generation of detectors. Other 250 mK cryostats can be retroftted in the same way. This confguration will meet the cryogenic requirements for single-wafer testing, providing 5–10 μW of cooling power at 100 mk for over 8 h. The system operates in a closed cycle, thereby avoiding external gas connections and cold o-rings. No moving parts are required, with the system operated entirely by heaters.
A dual-polarization receiver for multi-beam interferometry
Abstract:
Superconductor/Insulator/Superconductor (SIS) mixers are today the best heterodyne receivers for detecting astronomical signals in the range from 100 GHz to 1 THz. Existing receivers have noise performance approaching the fundamental quantum limit, but large format arrays have not yet been realised. Developing large format arrays is, therefore, the most efficient method for increasing the observational speed.
In this thesis, we describe the development of a planar dual-polarisation SIS receiver. The integration of the receiver circuit on the chip with the SIS mixers for both polarisations simplifies the receiver architecture. Upon this more compact receiver design, extending to a large focal plane array with a high pixel count is simplified. The cost of this simplified receiver is the need for the development of more complicated on-chip circuits. We demonstrate this technology development in the frequency band of the wideband Submillimetre Array (wSMA) low band from 190 GHz to 290 GHz. The dual-polarisation receiver chip with a size of 4.0 mm by 4.1 mm comprises a polarisation splitting 4-probe orthomode transducer (OMT) and the mixers for each polarisation. All planar circuits are fabricated on the same quartz chip alongside some auxiliary circuits needed to connect the OMT with the mixers. We use the twin junction tuning scheme because it offers a compact and robust way of matching the highly capacitive SIS junctions.
As part of this development, we investigate the twin-junction tuning to improve the matching to the feeding RF circuit during the design phase. Furthermore, we extended existing techniques of embedding impedance recovery to apply to twin junction mixers to have a reliable tool to test our integrated receiver experimentally.
Based on these ideas, we designed an on-chip dual polarisation receiver, deployed it in a test setup and finally characterised the receiver. We describe in detail the test setup, including the 40 mm by 40 mm mixer block, which reserves margins on the size for the IF board and the magnetic bias options, and allows the extension into a 2x2-pixel 70 mm by 70 mm array. The preliminary experimental results we obtained with a single receiver chip demonstrate that sufficient local oscillator (LO) power can be coupled on the receiver chip, and it lines out a procedure for testing and characterising the receiver.
In addition, we present the design of a two-pixel balanced dual-polarisation receiver with an on-chip LO distribution. The design uses the same method we employed for the receiver chip described above but has the capability of rejecting LO noise. This design allows the construction of large format SIS receiver arrays with an improved noise temperature performance.