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Slot antenna SIS mixers for submillimeter wavelengthsWe are developing improved versions of a slot antenna SIS mixer which we have previously described. The initial work demonstrated a double sideband noise temperature of 420 K for a 500 GHz quasi-optical SIS mixer employing a twin-slot antenna on a quartz dielectric substrate. A quartz hyperhemispherical lens is used to focus the incoming radiation onto the twin-slot antenna. The advantages of a twin-slot antenna include a low impedance (35 omega) and a clean, symmetric beam pattern into the dielectric with a 70 percent efficiency. In our original mixer, the radiation was coupled from the two slot antennas onto superconducting microstrip lines which fed the SIS junction. By performing an impedance transformation using tapered lines and by feeding the radiation from the two slots to the junction in parallel, the effective (real) impedance seen by the junction was reduced to just 4 omega. This very low impedance allowed a junction area of 2.3 sq micron to be used at 500 GHz, which was manufactured using optical lithography. However, no attempt was made to tune out the junction capacitance. We estimate that this capacitance reduces the impedance coupling efficiency to eta(sub Z) approx. equals 0.23, for our junction with omega R(sub N) C = 5.3 at 500 GHz. The recent development of techniques using electron-beam lithography to manufacture junctions with very small areas (approx. equals 0.1 sq microns) now allows considerably more flexibility in the design of SIS mixer circuits. We have redesigned the slot-antenna mixer to take advantage of this possibility. In particular, we have included a novel circuit which allows the junction capacitance to be tune out over a broad bandwidth. For instance, mixers designed for 800 GHz using NbN/MgO/NbN junctions with realistic parameters achieve a 3 dB impedance bandwidth of nearly 400 GHz. Furthermore, our circuit uses only short lengths of microstrip and should be less sensitive to RF losses than other designs. The improved impedance match should give a large reduction in noise temperature as compared to our previous mixer. The new devices are currently under fabrication. Further details of the design and any available experimental results are discussed.
Document ID
19930018556
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Zmuidzinas, Jonas
(California Inst. of Tech. Pasadena, CA, United States)
Leduc, Henry G.
(Jet Propulsion Lab. California Inst. of Tech., Pasadena., United States)
Stern, J. A.
(Jet Propulsion Lab. California Inst. of Tech., Pasadena., United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1992
Publication Information
Publication: Michigan Univ., The Third International Symposium on Space Terahertz Technology: Symposium Proceedings
Subject Category
Communications And Radar
Accession Number
93N27745
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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