M.A. Tarasov

Integrated rf amplifier based on dc SQUID

Integrated radio-frequency amplifiers comprising a 4-loop dc SQUID, seriesly connected input coil turns, a resonant capacitor parallel to the input coil, series capacitors at the input and output ports and bias resistors have been designed, fabricated and experimentally studied. A multiloop dc SQUID with parallel loops and seriesly connected single-turn input coils placed inside each loop and integration with the input resonant matching circuit elements and with elements of dc bias circuit allows one to increase signal frequency and reduce the influence of external noise. The amplifiers with three different capacitors have resonant frequencies 560, 656, 758 MHz and bandwidth about 50 MHz. The noise temperature of such amplifiers below 1.5 K has been measured using cold attenuator and room-temperature noise sources. The layout comprising three pairs of such amplifiers placed on the same 15/spl times/24 mm substrate was designed to increase the bandwidth over the bandwidth of the individual amplifiers.<<ETX>>

Low noise completely quasioptical SIS receiver for radioastronomy at 115 GHZ

Completely quasioptical heterodyne SIS receiver for radioastronomical applications at 115 GHz was designed and tested. Gaussian beam two lens input guide system and open structure SIS mixer with immersion lens were used. Integrated quasioptical structure consists of planar equiangular spiral antenna and superconductor—insulator—superconductor (SIS) tunnel junction as a mixing element connected to the antenna via microstrip impedance transformer. The best SIS mixer noise temperature at hot input and for heterodyne frequency 109.8 GHz with IF central frequency 1.4 GHz (DSB) was 28±7 K at the first quasiparticle step and 8±6 K at the second step.

DC SQUID RF amplifiers

The noise and signal parameters of several types of RF amplifiers based on different SQUIDs with integrated and hybrid input coils were studied. A new type of multiloop DC SQUID with an integrated input coil and extremely low stray capacitances was designed. The inductance of a four-loop SQUID was 100 pH, the input coil inductance 1.3 nH, and mutual inductance 300 pH. The tuned integrated four-loop amplifier at 420 MHz had a noise temperature lower 0.5 K and a power gain of nearly 20 dB in a 60-MHz bandwidth. For the noise calibration of such amplifiers, SIS junctions were used as a shot noise source, or a cooled attenuator and a room temperature semiconductor noise source were used. >

Studies of Josephson Mixing in SIS Junctions

Integrated receiving structure comprising self-Babinet-complementary spiral antenna and two SIS junctions connected in series via two matching microstrip structures has been designed, fabricated and experimentally studied. The calculated microwave responsp for such receiving structure has two maxima at 450 and 900 GHz. Direct detector response of such receiving structures has been measured using Fourier Transform Spectrometer in the frequency range 0.1 ¿1 THz. Microwave mixer performance has been measured with 500 GHz band LO source. The Josephson conversion with noise temperature of about 100 K was observed in the vicinity of the first Shapiro step at about 0.95 mV corresponding to 475 GHz signal frequency and with noise temperature 360 K near the second step at 1.8 mV corresponding to 900 GHz signal frequency. To prove that it was correct frequency down conversion the additional experiment was performed at first Shapiro step using the 4-th harmonic of Gunn oscillator 4×120 GHz instead of hot/cold load signal source.

Integrated receiving structure comprising complementary spiral antenna and tuned parallel biased SIS array

A type of superconducting receiving element comprising a complementary spiral antenna and a series-parallel superconductor-insulator-superconductor (SIS) array with individual tuning of each SIS junction has been designed, fabricated, and experimentally studied. The array was designed for the 80-160 GHz waveband and consists of five SIS junctions, each with a 1.5- mu /sup 2/ area, six inductive short-ended slotlines, and two decoupling capacitances. The effective direct detector bandwidth of this structure with a quantum efficiency equalling unity has been estimated to be as wide as 70 GHz. The noise temperature of the heterodyne mixer has been measured in a three-lens Gaussian beam guide by means of the hot/cold load method, yielding a receiver DSB noise temperature of 80 K. The intermediate-frequency (IF) mixer port load bandwidth and the effect of thermal background radiation on the I-V curve and the saturation of the SIS mixer have been studied.<<ETX>>

Superconducting Tunnel Junction Noise Generator and SIS Mixers Noise Measurements

In this work the output noise calibration of cryogenically cooled low noise SIS mixers, direct detectors and IF amplifiers by means of SIS noise source was studied experimentally. Applying LO power sufficient to linearize IV curve of SIS one may vary noise temperature from 4,2 to 100 K by changing bias current. Shot noise in series arrays of SIS junctions differs from noise in single junction.

DC SQUID RF amplifier with external mm-wave pumping and its testing by SIS junction noise

The power gain and the noise temperature of a DC SQUID RF amplifier at a signal frequency 400 MHz were measured in the presence of external microwave radiation at 2 cm, 8 mm and 4 mm wavelengths. The authors used a four-loop planar DC SQUID with an integrated input coil and very low values of inductances and stray capacitances. In the noise measurements they used an SIS junction as a precise source of input noise at high DC bias voltage Vb>V2 Delta . In such a configuration the studied system is the same as an SIS mm-wave mixer with a SQUID IF amplifier.

Subharmonically pumped SIS mixer

SIS harmonic mixer based on quasioptical structure with equiangular planar spiral antenna was investigated. SIS junction capacitance was resonated out by integrated circuit elements. Conversion losses, saturation power and noise were measured for quantum and nonquantum LO frequency operation. Nb-Al2O3-Nb SIS junctions and 75 GHz, 37.5 GHz, 25 GHz and 9.4 GHz LO frequencies (1, ?, ? and ? of signal frequency 75 GHz) were used.

Performance margins and application area of SQUID amplifiers

A series of dc SQUID radiofrequency amplifiers in the frequency range 0.1-1.1 GHz with noise temperature 0.4-2 K has been designed, fabricated and experimentally studied. For resonant input tank circuit an analytical model of noise temperature has been developed. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coeff 1 cient has been observed experimentally and described analytically and numerically. Application of SQUID amplifiers as IF amplifiers in SIS, Josephson, hot-electron heterodyne detectors as well as in cellular base stations has been discussed.

Hilbert transform spectrometer using shunted SIS junctions

A millimeter-wave spectrometer using the Hilbert transformation of the resistively-shunted SIS junction response has been designed, fabricated and experimentally studied. The SIS junctions have been used as a Josephson sensor placed in the center of complementary logarithmic spiral antenna. The response was studied in 75-150 GHz frequency band. The resolution below 1 GHz and noise equivalent power about 10¿13-10¿14 W has been measured for the 0.7 ¿ junction. The measured spectrum has been obtained by means of the Hilbert transformation via novel deconvolution program based on the maximum likelihood approach. This allows to diminish the measured interval of bias voltage and to avoid contribution of the noisy part of response curve without loss of the spectral resolution.