Ghassan Yassin

Abstract:

In this paper, we describe the design of a planar superconducting on/off switch comprising a high normal resistance nano-bridge deposited across a slotline transmission line. We present preliminary experimental results measured at 220 GHz range, and we discuss in detail the various parameters that affect the performance of the planar on/off switch, including the optimum thickness required for the nano-bridge to achieve high dynamic range and low transmission loss. The analysis is done by combining the accurate superconducting surface impedance description with rigorous electromagnetic simulations, and comparing the simulated results with the measured performance of a previously fabricated on/off switch fed by a backto- back unilateral finline taper. Finally, we propose an improved method to further increase the dynamic range of the switch, by introducing a multi-bridge design to tune out the residual inductance of the nano-bridges.

Abstract:

Modern ground-based radio-telescopes have stringent requirements on the receiver's feed-horn performance. These include a bandwidth covering a full atmospheric window from good sites (∼ 30%), low cross polarization and high beam circularity. In addition the unprecedented sensitivity required by recent proposed experiments requires large format focal plane arrays consisting of a large number of high performance feeds. While these feeds are straightforward to fabricate at microwave frequencies, the tight tolerances required in the THz region makes the realization of a large format array both expensive and time consuming. In this paper we describe feed designs that can be fabricated cheaply and rapidly without compromising the science requirements within the operating bandwidth. We present simulated and measured far-field beam patterns showing low sidelobe levels, good beam circularity and low cross-polarization levels over a fractional bandwidth of 20%. Having demonstrated the efficacy of our horn designs and fabricating technique experimentally, we have designed, fabricated and tested a prototype focal plane array of 37 hexagonally close packed horns milled in a single block of aluminum. Experimental testing of the radiation patterns of the array feeds demonstrated that they were essentially identical to the patterns of the feeds fabricated individually and that cross coupling between adjacent feeds was negligible. © 2013 IEEE.

Abstract:

Here we describe our work designing multiple flare-angle horns, optimised using a genetic algorithm. Several horns designs will be described and experimentally measured beam patterns for horns at 230 GHz will be presented. In addition, we will present new, wide bandwidth horns offering good performance over a ∼30% bandwidth. © 2013 IEEE.