Multiple flare-angle horn feeds for sub-mm astronomy and cosmic microwave background experiments
Astronomy & Astrophysics EDP Sciences 532 (2011) a61
Performance of a 700 GHz unilateral finline sis mixer
22nd International Symposium on Space Terahertz Technology 2011, ISSTT 2011 (2011) 175-178
Abstract:
We present a novel design and the measured performance for a superconductor-insulator-superconductor (SIS) mixer, operating near the superconducting gap of niobium (Nb), in the frequency range of 600-700 GHz. A key feature of the mixer design is the employment of a unilateral finline taper to provide smooth transition from the high-impedance waveguide mode to the low-impedance of planar circuits suitable for the operation of SIS tunnel junction. This geometry of the transition can be electromagnetically modelled and optimised to give a short mixer chip with wide RF bandwidth. The finline taper and all the superconducting transmission lines are integrated on-chip and deposited on a 60 μm thick quartz substrate. This results in an extremely simple mixer block design, comprising a feed horn and a straight waveguide section; no backshort or any mechanical tuning structure is needed. In this paper, we describe the design of the mixer chip, including full electromagnetic simulations of the passive circuits, combined with the heterodyne mixer gain and noise temperature predictions.We have tested the mixer performance from 595 GHz to 702 GHz and measured best receiver noise temperature of 145 K at 600 GHz, corrected for a beam splitter of 75 μm thickness. The need for a thick beam splitter was caused by the lack of sufficient power from the local oscillator (LO) which was optimised between 630-720 GHz and because our mixer was tuned low as a result of larger than designed tunnel junction. Nevertheless, our investigation has demonstrated that superconducting finline mixers work well at high frequencies and have several advantages over other designs, in particular simple mixer block and large substrate for integration of planar circuits.The experimental demonstration of a low-cost 37-horn focal-plane array consisting of smooth-walled multiple flare-angle horns fabricated by direct drilling
22nd International Symposium on Space Terahertz Technology 2011, ISSTT 2011 (2011) 139-142
Abstract:
In previous work, we have described novel smoothwalled multiple flare-angle horns designed using a genetic algorithm. A key feature of these horns is that they can be manufactured very rapidly and cheaply in large numbers, by repeated direct drilling into a single plate of aluminium using a shaped machine tool. The rapid manufacturing technique will enable the construction of very low cost focal-plane arrays, offering an alternative to conventional electroformed corrugated horn arrays. In order to experimentally demonstrate the new technology, we constructed a 230 GHz focal-plane array comprising 37 smooth-walled horns fabricated by direct drilling. We present the measured beam patterns for a large sample of these horns across the array, demonstrating the suitability of our manufacturing techniques for large format arrays. We have measured the cross coupling between adjacent feeds and have shown that it is negligible. We also present high quality beam patterns measured for a much smaller 700 GHz horn, showing the promise of extending this technology to THz frequencies.Designs of broadband unilateral finline sis mixers employing 15 μm silicon-on-insulator substrate at THz frequencies
21st International Symposium on Space Terahertz Technology 2010, ISSTT 2010 (2010) 171-178
Abstract:
We present the design of two niobium singleended Superconductor-Insulator-Superconductor (SIS) mixers optimized to work in the frequency range of 600-700 GHz. A key feature of this new mixer design is the utilization of a unilateral finline taper. This transition is significantly easier to design and simulate than the previously employed antipodal finline, and more importantly it simplifies the chip fabrication considerably since the fins do not overlap at any stage. RF power propagating in the finline is coupled to the microstrip either directly from the slotline to microstrip, or more efficiently via a coplanar waveguide (CPW). Another novel feature of our design is the fabrication of the mixer chip on a very thin silicon substrate which will be achieved using Silicon-On-Insulator (SOI) technology. This will allow easy matching of the incoming signal from the feed horn to the loaded waveguide and allows the lightweight mixer chip to be held in the E-plane of the waveguide using gold beam leads, eliminating the need for a deep groove in the waveguide wall. These new features yield a significantly shorter chip and allow wider RF bandwidth since the excitation of higher order modes in the groove has been avoided. The mixer block is extremely simple, composing a smooth-walled horn and a waveguide section without any complicated mechanical features. In this paper, we present the details of the mixer chip, including various transition sections, tuning circuits and mixer block designs, supported by electromagnetic simulations. We describe the design procedure in detail and predict the full mixer performance using the SuperMix software package.Measured performance of a 230 GHz prototype focal-plane feedhorn array made by direct drilling of smooth-walled horns
21st International Symposium on Space Terahertz Technology 2010, ISSTT 2010 (2010) 91-96