Comparison of measured and predicted performance of a SIS waveguide mixer at 345 GHz

The measured gain and noise of a SIS waveguide mixer at 345 GHz have been compared with theoretical values, calculated from the quantum mixer theory using a three port model. As a mixing element, we use a series array of two Nb-Al2O3-Nb SIS junctions. The area of each junction is 0.8 sq microns and the normal state resistance is 52 omega. The embedding impedance of the mixer has been determined from the pumped DC-IV curves of the junction and is compared to results from scale model measurements (105 x). Good agreement was obtained. The measured mixer gain, however, is a factor of 0.45 plus or minus 0.5 lower than the theoretical predicted gain. The measured mixer noise temperature is a factor of 4-5 higher than the calculated one. These discrepancies are independent on pump power and are valid for a broad range of tuning conditions

A low noise 410-495 heterodyne two tuner mixer, using submicron Nb/Al2O3/Nb tunneljunctions

A 410-495 GHz heterodyne receiver, with an array of two Nb/Al2O3/Nb tunneljunctions as mixing element is described. The noise temperature of this receiver is below 230 K (DSB) over the whole frequency range, and has lowest values of 160 K in the 435-460 GHz range. The calculated DSB mixergain over the whole frequency range varies from -11.9 plus or minus 0.6 dB to -12.6 plus or minus 0.6 dB and the mixer noise is 90 plus or minus 30 K

Photon-assisted Tunneling In Double-barrier Superconducting Tunnel-junctions

Double-barrier Nb/Al2O3/Al/Al2O3/Nb tunnel junctions are used as mixing elements in a 345 GHz waveguide mixer. Noise temperatures (double side band) down to 720 K at 3.0 K are obtained without the need to apply a magnetic field to suppress the Josephson current. It is shown that the composite barrier acts as a single barrier for photon-assisted tunneling. Surprisingly, at these frequencies the capacitance of two stacked tunnel barriers is only determined by one barrier

Extensive test of the three‐port quantum mixer theory on 345 GHz superconductor‐insulator‐superconductor mixers

Predictions of the three-port model of the quantum theory of mixing are compared with measured results on 345 GHz superconductor-insulator-superconductor waveguide mixers. Single Nb-Al2O3-Nb tunnel junctions or two or four identical junctions in series are used as mixing elements. Two different waveguide mixerblocks, one with two tuners and another with one tuner, are used. In addition a single junction with integrated tuning stub is analyzed. Embedding impedances are obtained from fits to the pumped I-V curves for all three types of mixing elements. In all cases the dependence of mixer conversion and mixer noise on bias voltage, pump power, and embedding impedance is well described by the three-port model. The measured mixer gain is lower than the calculated gain by a factor of 0.35-0.65, independent of the type of mixer. The use of an additional integrated tuning element does not change this factor. It is concluded that an excess noise power equivalent with a blackbody source of 40-65 K must be added to the mixer noise to account for the absolute value of the observed noise power

Quantum limited responsivity of a Nb/Al2O3/Nb SIS waveguide mixer at 460 GHz.

The noise and gain behaviour of a Nb/Al2O3/Nb SIS waveguide mixer, with an on chip integrated tuning element, is analyzed at 460 GHz. The receiver sensitivity of the whole system, including the beamsplitter, window and lenses is 116 K DSB. The mixer noise temperature is 35 +/- 20 K. Within the experimental error this is as low as the quantum limit at 460 GHz. This is the first measurement of quantum limited sensitivity above 400 GHz. We compare data of the pumped I-V curves with the Werthamer-Tucker theory and demonstrate an excellent agreement at 460 GHz. A comparison of the measured IF-output noise versus bias voltage with the quantum theory of mixing shows a good agreement, indicating for the first time the applicability of this theory to Nb tunnel junctions up to 500 GHz

Evaluation of niobium transmission lines up to the superconducting gap frequency

The frequency dependence of the coupling of niobium superconducting transmission lines is measured for frequencies up to and above the superconducting gap frequency. For this purpose superconducting microstrips are integrated in log-periodic planar antennas and the spectral response is measured by means of a Fourier transform spectrometer with 1 mum2 Nb/Al2O3/Nb SIS junctions as detectors. Resonances of microstrips are observed up to 650 GHz, the superconducting gap frequency of niobium, but above that frequency no resonances have been detected. The measured resonance frequencies are in good agreement with a dispersive model for superconducting transmission lines based on the Mattis-Bardeen theory. The radiation coupling is lower than calculated, indicating significant dielectric losses

Ein Lehrmodell zur Implantation von Totalendoprothesen des Hueftgelenks nach Charnley

SIGLETIB: RO 148 (12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman