Superconducting quantum detectors

Abstract:

We present a new type of waveguide to microstrip transition designs for a 700 GHz SIS mixer. The transition comprised a unilateral finline taper and the RF power from the finline slot is coupled through coplanar waveguide to microstrip using two radial stubs. This transition is significantly easier to design and fabricate than the conventional antipodal finline taper since the fins do not overlap at any stage. A key feature of this design is that it can be deposited on Silicon-on-Insulator resulting in a finline mixer chip on approximately 15 µm silicon substrate. This allows the mixer chip to be held in the E-plane of the waveguide without a supporting groove in the waveguide wall, avoiding the excitation of higher order modes. The chip is simply supported by gold leads deposited on the substrate. It should be emphasized that the employment of such substrate will also decrease the loss and allow finline mixers design to be extended to the THz region.

Abstract:

This paper describes a new Heterodyne Array Receiver Program (HARP) and Auto-Correlation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope. The 16-element focal-plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three-dimensional) mapping speeds, along with significant improvements over single-detector counterparts in calibration and image quality. Receiver temperatures are ∼120 K across the whole band, and system temperatures of ∼300 K are reached routinely under good weather conditions. The system includes a single-sideband (SSB) filter so these are SSB values. Used in conjunction with ACSIS, the system can produce large-scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully sampled maps of size can be observed in under 1 h. The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large-scale unbiased surveys of galactic and extra-galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three-dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARPACSIS will provide highly complementary science programmes to wide-field continuum studies and produce the essential preparatory work for submillimetre interferometers such as the Submillimeter Array (SMA) and Atacama Large MillimeterSubmillimeter Array (ALMA). © 2009 RAS.

Abstract:

We describe the design and testing of an easy-tomachine smooth-walled horn which exhibits excellent beam circularity and low cross polarisation over a relatively large bandwidth. The design comprises three coaxial conical sections and two flare discontinuities joining the three sections together. The discontinuities generate appropriate higher order modes which combine to give a circular field distribution at the aperture. The positions and sizes of these discontinuities were calculated using a genetic algorithm. The horn was fabricated either by using the well known electroforming method or simply by a drill tool, shaped into the horn profile, and a standard mill. The measured radiation patterns or the electroformed horns show good excellent circularity and agree well with the calculated curves. They also show that the three-section horn has a substantially wider bandwidth than the conventional Potter horn. Preliminary measurements of the drilled horns patterns are also shown and compared with theory.