Superconducting quantum detectors

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:

In this letter, we present a new E-plane rectangular waveguide bend that can be micromachined using split-block fabrication. The 90° bend is created by machining two linear channels with a notch left in the outside corner. This notch significantly improves the return loss and the insertion loss of the bend. The primary advantage of this technique is that it produces a compact waveguide bend, minimizing both the size and the conduction loss of the waveguide circuit. Another advantage is that this technique only requires linear channels to be machined, thus it can be fabricated without requiring a computer numerically controlled (CNC) milling machine. The performance of this waveguide bend was optimized using electromagnetic simulation software, and the optimal reflection coefficient was found to be below -28 dB across the entire operational bandwidth of the waveguide. The simulated design was then validated using two experimental prototypes that were tested at microwave (12-18 GHz) and millimeter frequencies (140-220 GHz).

Abstract:

A new 1x4 focal plane array centered around 230 GHz is presented in this paper. The size of the array was limited to 4 pixels due to the space available in the test cryostat; however, we can expand the design in the future. On the front of the array block there are 4 waveguides flanges for the RF feed horns, while the local-oscillator signal enters through a separate waveguide on the side. The local-oscillator power is multiplexed using cascaded E-plane power dividers and then combined with the RF signals using directional couplers. Preliminary tests of the array block have now been completed. They show reasonable local-oscillator distribution and excellent RF signal isolation. Future work will involve testing the noise properties of the array block and improving the local-oscillator distribution.

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.