ISSTT Proceedings

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Quasi-Optical SIS Mixer with a Silicon Lens for Submillimeter Astronomy

Authors:
N.G. Ugras, J. Zmuidzinas, H.G. LeDuc
Abstract:
We have designed and tested a quasi-optical low-noise SIS receiver for the submillimeter band. The radiation is focused onto a twin slot antenna by a hyperhemispherical silicon lens. The forward coupling efficiency for silicon ([epsilon]r=11.7) is 91% compared to 70% in quartz ([epsilon]r=4.5). However the relatively high dielectric constant of silicon would cause a reflection loss of [approx. equal to]30% at the front surface of the lens compared to [approx. equal to]15% in quartz. We have eliminated this reflection loss by antireflection coating the lens with an alumina loaded epoxy ([epsilon]r=4.0). A uniform epoxy thickness of 68µm (=[lambda]/4 at 550 GHz) over the hemispherical lens is obtained by diamond machining the surface. The twin slot antenna has good directivity and a low impedance which is well matched to the rf impedance of the SIS junctions. The mixer circuit consists of two SIS junctions separated by a superconducting microstripline acting as the tuning inductance. The area of the tunnel junctions ranges between 0.56-1.56 µm², with a current density of 10,000A/cm², and Rsg/Rn[approx. equal to]15. Preliminary results indicate typical receiver noise temperatures ranging from 130 K to 160 K in the 500 to 600 GHz band. The spectral response of the mixer agrees well with the direct detector response obtained by a Fourier transform spectrometer. The measured input beam pattern is well collimated and has a Gaussian distribution. This receiver is being used for radioastronomical observations aboard NASA's Kuiper Airborne Observatory.
Categories:
SIS Receivers
Year:
1994
Session:
1
Full-text:
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Page Number(s):
125