In this letter we present the characterization of the first frequency up-converter using distributed superconducting tunnel junctions. The power of the frequency up-converted signal was large enough to pump an SIS mixer. The efficiency of the distributed superconducting tunnel junction is 11-22 % for a fractional bandwidth of 7% with excellent spectral line purity. The -3 dB line width of the up-converter signal is better than 1 Hz, which was the lowest resolution bandwidth of the spectrum analyzer.
In this letter we present the characterization of the first frequency up-converter using distributed superconducting tunnel junctions. The power of the frequency up-converted signal was large enough to pump an SIS mixer. The efficiency of the distributed superconducting tunnel junction is 11-22 % for a fractional bandwidth of 7% with excellent spectral line purity. The -3 dB line width of the up-converter signal is better than 1 Hz, which was the lowest resolution bandwidth of the spectrum analyzer.
In this paper, we present the analysis, design, and characterization of the first frequency multiplier using distributed superconductor-insulator-superconductor (SIS) junctions. We derived analytical expressions describing the properties of the distributed SIS junction as a frequency multiplier. The modeling of the distributed SIS junctions shows that high conversion efficiency can be achieved when used as the multiplier. The measured output power generated by such multiplier employing the distributed SIS junction at the second harmonic of the input frequency is in good agreement with the model. Furthermore, the frequency multiplier based on the distributed SIS junction for the first time was able to pump an SIS mixer. The multiplication efficiency of the distributed SIS junction is 15-30% for a fractional bandwidth of 10% with excellent spectral line purity. The -3 dB line width of the multiplied signal is 1 Hz, which was limited by the resolution bandwidth of the spectrum analyzer. The results attained in this paper show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-end and multipixel SIS mixer receivers.
We experimentally investigate different mixing regi-mes in Nb/AlOx/Nb and Nb/AlN/NbN tunnel superconductor-insulator-superconductor (SIS) junctions. The SIS mixers were studied with regard to the following modes of operation: in an extremely low-frequency range (0.1-20 GHz) and as high harmonic mixers; n ≈ 20-30 at signal frequencies of about 500 GHz that requires high power of a local oscillator. The quasiparticle and Josephson mixing regimes have been compared. We demonstrate that, in some applications requiring high conversion efficiency, the Josephson regime can be more preferable than the quasiparticle regime due to a larger output signal and better signal-to-noise ratio. As an example of such an application, we consider the phase locking of a THz oscillator using a cryogenic harmonic phase detector, which only ought to realize all of its benefits under the Josephson mixing regime. In addition, we demonstrate that the presence of the Josephson effect results in considerable increase in conversion efficiency at the expense of the dynamic range decrease; it was measured for low-frequency up- and down-convertors, which are promising for cryogenic multiplexing systems.
This chapter discusses the high sensitivity superconducting mixers, i.e. detectors used in heterodyne receivers. Today, there are essentially two very successful concepts of superconducting mixers, or frequency down-converters, the superconductor-insulator-superconductor tunnel junction SIS mixer and the superconducting hot-electron bolometer mixer. Moving up to higher frequencies in the microwave and millimeter wave electromagnetic spectra makes it more and more difficult to retrieve a good signal-to-noise ratio with ordinary solid-state amplifiers. The driving force for using superconducting mixers is their excellent down-conversion efficiency and capability to down-convert RF signals from microwave frequencies up to the terahertz region. The main purpose of a receiver is to pick up and amplify a weak signal, which can then be accurately determined in amplitude and phase. The mixer noise temperature and conversion gain are the most important parameters for the mixing device. The Josephson junction mixer was one of the first suggested devices based on superconducting point contacts and later tunnel junctions.
This thesis focuses on the development of advanced components for the future wideband side band separating and / or multipixel receivers for radio-astronomy with ultimate sensitivity.\nIn this thesis, a novel frequency multiplier based on distributed superconducting tunnel (SIS) junctions has been demonstrated for the first time, taking advantage of the extreme inherent nonlinearity of such device. This practical demonstration is the result of an extensive theoretical exploration and modelling, showing the importance of the reactive quasi-particle tunnel current\nand its impact on the SIS tunnel junction frequency multiplier. In addition, a novel technique\nwas suggested that allows for the first time direct measurement of the reactive quasi-particle tunnel current.\nThis work comprehends the analysis, design and characterisation of the first frequency multiplier using distributed SIS junctions. The measured output power generated by the distributed SIS junction at the second harmonic of the input frequency were in good agreement\nwith the model. Furthermore, the distributed SIS junction as a frequency multiplier were for the first time able to pump an SIS mixer. An efficiency of the distributed SIS junction multiplier of 15-30 % for a fractional bandwidth of 10% with excellent spectral line purity were\ndemonstrated. The -3 dB line width of the multiplied signal is better than 1 Hz, which were the lowest resolution bandwidth of the spectrum analyser. Consequently, the results attained in this work show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-ended and multi-pixel SIS mixer\nlayouts.\nFurthermore, in order to improve the sideband rejection ratio of cryogenically cooled sideband separating receivers for radio astronomy receivers to more than 15 dB over a wide RF and IF bandwidth, novel wideband RF and IF hybrid couplers have been developed and demonstrated\nwith very low imbalances. More specifically, a 4-8 GHz IF assembly comprising a compact 90° hybrid chip, two bias-T circuits and two transmission line circuits was designed and characterised. The compact size of the hybrid chip allows it to be integrated into virtually any sideband separating (2SB) mixer operating at cryogenic temperatures and is furthermore especially advantageous for multi-pixel 2SB receivers or low noise balanced amplifier layouts.\nThe characterisation of the hybrid assembly was performed at a cryogenic temperature of 4 K and sophisticated calibration and fixture de-embedding procedures were used. To further improve the sideband rejection ratio, a novel design for a RF 90° waveguide hybrid with very\nlow amplitude imbalance over a fractional bandwidth of 30% (159-216 GHz) was demonstrated. Both Hybrids are currently implemented in the ALMA Band 5 receivers, which\nrepresent the state-of-the-art for ultra-low noise sideband separated receivers.\nIn order to allow complete characterisation of the ALMA Band 5 cartridge a highly versatile measurement setup has been built. The measurement setup includes all necessary hardware and achieves automatic measurements for the system noise and sideband rejection with in-built\noptimisation procedures. The measurement setup additionally comprises measurements of the receiver saturation, phase and amplitude stability, as well as optical beam characterisation.
We have investigated high-frequency limits of superconducting quasiparticle mixers from experiments on Al/Al-oxide-In/Al (or Ag) tunnel junctions, and from calculations based on Tucker’s quantum theory of mixing (QTM). The small superconducting energy gap of Al enabled us to study mixer performance at around the junction gap frequency, fg =(Δ1+Δ2)/h≊87 GHz, of superconductor-insulator-superconductor (SIS) mixers, and at twice the junction gap frequency for S-I-normal metal (SIN) mixers ( fg =Δ1/h) with available millimeter wave sources. Because of the low transition temperature of Al (Tc ≊1.3 K), a dilution refrigerator was used for providing temperatures below 1 K. The best mixer conversion efficiency was obtained for a low-resistance (∼34 Ω) six-junction array SIS mixer operated at f/fg ≊1 (in this case 73 GHz). The coupled single sideband conversion gain (with no image rejection) was −13.8 dB and the available conversion gain was estimated to −8.4 dB. Complicating nonequilibrium phenomena made it difficult to compare the performance of these relatively high-current-density mixers to the QTM. However, good agreement between calculated and corresponding measured conversion efficiencies and dynamic resistance values was obtained for the low-current-density mixers. Noise due to switching between rf-induced Josephson steps and interference from Josephson mixing could be quenched by a magnetic field. Several high-frequency limits are considered in this paper (such as Josephson switching noise, nonequilibrium phenomena, pair breaking, and energy gap limitations). Our results indicate that submillimeter wave SIS mixer receivers are likely to perform well, at least up to their gap frequencies, i.e., the THz region for large gap superconductors. Our QTM calculations showed that conversion gain larger than unity should be possible up to twice the gap frequency. Above this frequency the conversion loss will increase rapidly.
Large intermediate-frequency (IF) bandwidth is of particular interest for heterodyne mixers, especially for those at THz frequencies. NbN superconductor-insulator-superconductor (SIS) junctions, with a gap frequency twice that of Nb, can be applied to mixers beyond 1 THz. The IF bandwidth of NbN SIS mixers, however, is yet to be fully understood. In this paper, we investigate the IF bandwidth of a 0.5 THz all-NbN SIS mixer. First, its IF bandwidth is numerically simulated in terms of the mixer conversion efficiency and time constant. Second, the mixer noise performance is experimentally characterized in the IF band of 0.5 ~ 12 GHz. Detailed theoretical simulation and experimental results will be presented.