Dr. Boon Kok Tan

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.

Abstract:

We present the first, complete 230 GHz feedhorn array manufactured by direct drilling of smooth-walled horns into a single plate of aluminium. The horn design process, based on a genetic algorithm, is described and the fabrication process, via direct drilling using shaped drill bits, is presented. We present cross coupling and beam pattern measurements of a close-packed pair of the smooth-walled horns fabricated in a single block of aluminium. We also present a prototype 37 horn array, again fabricated by drilling into a single block. Our measurements show that our designs and fabrication techniques will be robust when applied to large focal arrays of horns consisting of hundreds or thousands of feedhorns. We expect our smooth-walled horn designs and novel manufacturing techniques will offer an attractive, low-cost alternate to traditional horn arrays consisting of electroformed corrugated horns.