Ghassan Yassin

Abstract:

We present a new method to determine the contribution of the IF-amplifier chain to the overall noise performance of an SIS-based receiver. Using simulated I-V and IF power characteristics, we show that the standard method used to date to evaluate the IF noise can underestimate the contribution because of non-negligible curvature in the post-gap SIS I-V characteristic. We demonstrate that the new method is not susceptible to the post-gap curvature, and discuss its benefits and limitations to the accurate and precise evaluation of IF noise contributions.

Abstract:

Astronomical interest in millimetre and submillimetre wavelengths (f = 300 GHz to 1 THz) has fuelled the development of low noise high sensitivity detectors for these wavelengths. HARP (Heterodyne Array Receiver Project) will be a 16 element focal plane imaging array of heterodyne detectors for the 850 micron (325 - 375 GHz) band. Each element will consist of a mixer employing an SIS (superconductor - insulator - superconductor) tunnel junction as the non linear device. When attached to the James Clerk Maxwell Telescope in Hawaii the array will offer greatly improved mapping speeds of extended objects complementing existing bolometer detectors and planned millimetre wave aperture synthesis telescopes. This presentation will examine aspects of the SIS device physics, quasi-optics, and electromagnetic design for the HARP imaging array. Original results from computer modelling and experiments on a prototype mixer will be presented.

Abstract:

The water content in multilayers made from poly(styrenesulfonate) and poly(diallyldimethylammonium chloride) was determined using infrared spectroscopy and thermal gravimetric analysis. Under ambient conditions the polyelectrolyte multilayer contains 10-20 wt % water, which is removed by heating under dry conditions to 100 °C. FTIR comparison of multilayers with solution-precipitated polyelectrolyte complexes of the same polymers revealed that both the composition and sulfonate group environment were identical.

Abstract:

The authors report the successful operation of an antipodal finline quasi-particle SIS mixer at 230GHz. The mixer is fed by a waveguide diagonal horn and uses planar circuit technology and integrated tuning. The mixer is testd over the frequency range 213-265GHz and a receiver noise temperature of ≃60K DSB over the whole of this range is obtained. This work has shown that superconducting finline mixers have low noise and are easy to manufacture, and are therefore suitable for large-format imaging arrays.