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Abstract:

We present the design of an 8-pixel Superconductor-Insulator-Superconductor (SIS) array centred at 650 GHz, which comprises two nearly identical 1×4 planar array chips, stacked together to form a 2×4 focal plane array. The array is fed by a single local oscillator (LO) source, and the array size is extendable by either increasing the number of mixing elements in the array chip or the number of stacking. The LO and RF signals for each mixer in the array are combined on-chip via a microstrip-coplanar waveguide (CPW) crossover which allows control of the RF/LO coupling level for each mixing element. The use of this planar beam splitter enables us to simplify greatly the design of the array mixer chip, as well as the design of the mixer block, which is important for future large pixel arrays. In this paper, we describe the design of the various components of the array chip, and the design of the mixer array block including the simplified LO distribution network.

Abstract:

In this paper, we present the design of a resonance phase-matched Josephson travelling-wave parametric amplifier that have a 12GHz 3 dB-bandwidth centred near 10 GHz. Our design utilises a unilateral planar circuit structure which requires only a single layer of thin superconductor film deposited on a 91̽»¨ing substrate to reduce the fabrication complexity. The nonlinear medium of the device is provided by a series of Josephson junctions embedded in a coplanar waveguide with integrated shunt capacitor, and the dispersion of the transmission line is controlled by quarter wavelength resonators coupled capacitively to the feedline. Here, we describe in detail the electromagnetic designs of the various components of the amplifier, and the coupled-mode equations model that governs the three-wave mixing process. We extract the required circuit parameters of the amplifier through electromagnetic modelling, and determine the parametric gain-bandwidth product of the amplifier using an analytical model. Finally, we discuss the various design aspects that affect the overall performance of the amplifier.

Abstract:

We present the design of an integrated dual-polarisation superconductor-insulator-superconductor (SIS) mixer operating at ALMA Band 10 frequency range. All the RF components, including the orthomode transducer (OMT), the quadrature hybrid and the SIS mixer circuits, are designed as superconducting planar circuits to form a single planar mixer chip. The mixer circuits will be fabricated using standard thin film deposition technology on an ultra-thin silicon-on-insulator (SoI) substrate. In this paper, we discuss in detail the design of the various RF components that make up the complete dual-polarisation SIS mixer chip, and provide the predicted performance using rigorous electromagnetic modelling. The optimised designs of these components are then integrated in a superconducting quantum mixer circuit modelling (SuperMix) environment for assessing the performance of the heterodyne parameters of the mixer such as mixer gain and noise temperature.

Abstract:

We present the design of a four-port planar circuit beam splitter comprising a microstrip and a coplanar waveguide (CPW) crossing each other. The CPW is fabricated in the ground plane (bottom layer) and the microstrip is deposited on top of the dielectric layer. A small section of the microstrip line is bent and aligned parallel to the central conductor of the bottom CPW, allowing the level of power coupling to be easily controlled by changing the length of the aligned section. The simple layout of the planar beam splitter makes it easy to fabricate in a wide frequency range from microwave to submillimetre (sub-mm) wavelengths. In this paper, we describe in details the electromagnetic design of the planar beam splitter and its predicted performances in the frequency range of 600– 700 GHz. We discuss the potential usage of the planar beam splitter as a replacement to the free-space beam splitter in receivers, in particular those using superconductor-insulatorsuperconductor (SIS) mixer arrays. To investigate the integrity of our design in a controlled way we scaled the design to operate in the Ku-band and measured the performance of several prototypes experimentally. Our tests showed good agreement between the measured performance and simulations.

Abstract:

We have developed anSIS receiver with a wide intermediate-frequency (IF) bandwidth.This is important for reducing image integration time and simultaneously measuring multiple spectral lines. The receiver is a finline mixer-based design, which allows for ultra-wide radio-frequency (RF) bandwidth and has lower mechanical requirements compared to radial stub designs. Simulations of this receiver showed quantum limited noise in the RF frequency range of 140 to 260 GHzand from DC to 10GHz in the IF spectrum.We measured the noise temperature by comparing the receiver's response to hot and cold loads. The best noise temperature was 37.9 K at 231.0 GHz, and all of the results were below 100 K from 213 to 257 GHz (the bandwidth of our local-oscillator). We measured the IF bandwidth using a spectrum analyser, and found good results from around 3-10 GHz. The lower frequency was restricted by our IF amplifier's bandwidth but the higher frequency limit was lower than we expected from simulations. We believe that this discrepancywas due to the inductance of the bondwires that we used to connect the mixer chip to the IF board. We are currently investigating techniques to reduce and compensate for this inductance.