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Abstract:

DC blocks are used frequently in planar circuits to enable separate DC voltage/current biasing of active components inserted along the transmission lines. In this Letter, we present a slotline DC block design where the conductors of the transmission line can be physically broken, while allowing the propagation of the RF signal across the discontinuity with negligible insertion loss. The DC block comprises two break-lines with narrow gaps, patterned on the two ground planes of a slotline with each breakline connected to an RF choke. The RF chokes present open circuit nodes that prevent the RF power from leaking into the break-lines gaps. We have fabricated and tested the DC block, and demonstrated that the measured performance agrees very well with simulated results. The insertion loss was close to – 0.5 dB in the designated range of 12–16 GHz, demonstrating that the RF leakage through the DC block is indeed negligible.

Abstract:

We present a planar Yagi antenna that has an end-fire beam characteristic and broad operational bandwidth. Two dipoles with different lengths are cascaded together to broaden the bandwidth. Printed directors and truncated ground plane are employed to achieve high front-to-back gain ratio. The double-dipole antenna is fed directly with a microstrip, and hence is readily adaptable to most of the millimetre and sub-millimetre detector circuits. In this paper, we present the antenna design in the context of designing a 1.05 THz Superconductor-Insulator-Superconductor (SIS) mixer that is suitable for Atacama Large Millimetre/Sub-millimetre Array (ALMA) Band 11 receiver. Detailed analysis of the antenna design is discussed, and simulated far field beam patterns and bandwidth performance is presented.

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.