Ghassan Yassin

Abstract:

A theoretical technique was developed for simulating the quantum-mechanical multitone behavior of superconducting tunnel junction circuits. The procedure was based on a full quantum-mechanical description of photon-assisted tunneling. It was expected to be used to model saturation in submillimeter-wave SIS mixers. SIS mixers were used extensively in submillimeter-wave astronomy.

Abstract:

The feasibility of making single-chip, superconducting detectors for submillimetre-wave astronomical inteferometry is demonstrated. An experimental device based on back-to-back corrugated horns, and back-to-back finline transitions, was fabricated. The detector was illuminated at 350 GHz, using a coherent laboratory source, and 0.6° fringes were measured.

Abstract:

We describe a waveguide to thin-film microstrip transition for high-performance submillimetre wave and teraherz applications. The proposed constant-radius probe couples thin-film microstrip line, to full-height rectangular waveguide with better than 99% efficiency (VSWR ≤ 1.20) and 45% fractional bandwidth. Extensive HFSS simulations, backed by scale-model measurements, are presented in the paper. By selecting the substrate material and probe radius, any real impedance between ≈ 15-60 Ω can be achieved. The radial probe gives significantly improved performance over other designs discussed in the literature. Although our primary application is submillimetre wave superconducting mixers, we show that membrane techniques should allow broad-band waveguide components to be constructed for the THz frequency range.

Abstract:

We report the successful operation of a 700 GHz SIS finline mixer employing a Nb tunnel junction and Nb transmission lines. In particular, we discuss the properties of a new mixer feed and the influence of-tuning on the mixer performance. Experimental and simulation work shows that the performance of the mixer below the superconducting gap is strongly dependent on the electrical properties of the tuning stub, while at frequencies above the gap the mixer performance is dominated by both tuning and transmission lines losses.

Abstract:

We describe a procedure for modelling the optical behaviour of planar, bolometric imaging arrays. Arrays of this kind axe being developed for the next generation of ground-based and space-borne, submillimetre-wave and far-infrared, astronomical telescopes. A unique feature of the scheme is that the partially coherent vector fields associated with the individual pixels are traced through the optical system simultaneously. Simultaneous tracing is achieved by propagating the second-order statistical properties of the total field. In the paper, we describe the theoretical basis of our method, and present the results of a number of illustrative simulations.