Dr. Boon Kok Tan

Abstract:

We present a new software package for simulating the performance of Superconductor / Insulator / Superconductor (SIS) mixers. The package is called QMix (“Quasiparticle Mixing”) and it uses multi-tone spectral domain analysis (MTSDA) to calculate the quasiparticle tunneling current through the SIS junction. This technique is very powerful and it allows QMix to simulate multiple strong tones and multiple higher-order harmonics. We have compared this software to the experimental data from a 230 GHz SIS mixer, both to validate the software and to explore the measured results. Overall, we found very good agreement, demonstrating that QMix can accurately simulate the performance of SIS mixers. We believe that QMix will be a useful tool for analyzing experimental data, designing new SIS mixers, and simulating new applications for SIS junctions, such as frequency multiplication.

Abstract:

In this paper, we present preliminary measured performance of an SIS mixer employing a Nb/AIN/NbN tunnel junction in the frequency range of 780–950 GHz range. The mixer design is an upgrade of the Carbon Heterodyne Array of the Max-Planck-Institute Plus (CHAMP+) mixer, coupled with an easy to fabricate smooth-walled horn. The noise temperature of the mixer is measured using the standard Y-factor method, but all the RF optics is enclosed in the cryostat. We use a rotating mirror in the cryostat to switch between a room temperature load and a 4 K blackbody load. With this method, we have measured a noise temperature of 330 K around 850 GHz, corrected for a mismatch between a reduced height rectangular waveguide at the input of the mixer block and a full height waveguide at the output of the horn. To remove this mismatch we now plan to redesign a new mixer chip with a full-height waveguide backpiece. The expected performance of the new mixer chip is also reported.

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 supporting 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.