超导隧道结亚谐波混频器的研究

本文探讨了新型的超导隧道结亚谐波混频器。其混频作用是通过由超导体—隔离体—超导体(SIS)构成的隧道结完成。在性能上可同通常的Schottky二极管亚谐波混频器媲美,基于Tucker量子混频理论,对这种新型混频器进行了噪声和变频效率的分析研究。     

Performance of Arrays of SIS Junctions in Heterodyne Mixers

We have made a systematic experimental study of the performance of millimeter-wave quasiparticle heterodyne mixers which use arrays of SIS tunnel junctions. Sets of arrays with N =1, 5, 10, 25, and 50 junctions in series were fabricated by photolithography. All of the arrays in a given set were made on a single silicon wafer so that their response time parameter omega/sub S/R/sub N/C would be the same. Junction areas were scaled so that the total impedance was the same for each array in a set. Sets of arrays from four wafers with values of omega/sub S/R/sub N/C ranging from 2.6 to 13 were evaluated in mixers at 33 and 36 GHz. These measurements showed that the signal power required to saturate the mixers varies as N/sup 2/ and that the conversion efficiency is nearly independent of N for all values of omega/sub S/R/sub N/C. The mixer noise temperature is independent of N for large values of omega/sub S/R/sub N/C. Therefore, the dynamic range of an SIS quasiparticle mixer can increase in proportion to N/sup 2/. For small values of as omega/sub S/R/sub N/C, however, the mixer noise increases systematically with N. This correlation suggests that the junction capacitance affects the coupling between junctions that can contribute to the noise.     

A Tuning Circuit with Two Half-Wave Distributed Junctions for All-NbN SIS Mixers

A novel broadband tuning circuit composed of two low-current-density half-wave NbN/MgO/NbN tunnel junctions connected by a half-wave NbN/MgO/NbN microstrip line has been successfully tested in a quasi-optical mixer at frequencies above 700 GHz. The circuit had a designed center frequency of 870 GHz, was integrated in a center-fed twin-slot antenna, and was fed via a quarter-wave impedance transformer. Heterodyne measurments showed double-side-band receiver noise temperatures equivalent to 6-9 quanta from 675 to 810 GHz for a mixer with a current density of 6.7 kA/cm². The RF bandwidth was broader than that of a conventional mixer using a full-wave junction with the same current density.     

Magnetic Tunnel Junctions for Spintronic Memories and Beyond

In this paper, recent developments in magnetic tunnel junctions (MTJs) are reported with their potential impacts on integrated circuits. MTJs consist of two metal ferromagnets separated by a thin insulator and exhibit two resistances, low (R_p) or high (R_ap) depending on the relative direction of ferromagnet magnetizations, parallel (P) or antiparallel (AP), respectively. Tunnel magnetoresistance (TMR) ratios, defined as (R_ap $R_p)/R_p as high as 361%, have been obtained in MTJs with Co₄₀Fe₄₀B₂₀ fixed and free layers made by sputtering with an industry-standard exchange-bias structure and post deposition annealing at Ta = 400 degC. The corresponding output voltage swing DeltaV is over 500 mV, which is five times greater than that of the conventional amorphous Al-O-barrier MTJs. The highest TMR ratio obtained so far is 500% in a pseudospin-valve MTJ annealed at Ta = 475 degC, showing a high potential of the current material system. In addition to this high-output voltage swing, current-induced magnetization switching (CIMS) takes place at the critical current densities (J_CO) on the order of 10⁶ A/cm² in these MgO-barrier MTJs. Furthermore, high antiferromagnetic coupling between the two CoFeB layers in a synthetic ferrimagnetic free layer has been shown to result in a high thermal-stability factor with a reduced J_CO compared to single free-layer MTJs. The high TMR ratio enabled by the MgO-barrier MTJs, together with the demonstration of CIMS at a low J_CO, allows development of not only scalable magnetoresistive random-access memory with feature sizes below 90 nm but also new memory-in-logic CMOS circuits that can overcome a number of bottlenecks in the current integrated-circuit architecture     

Deterministic modelling of indoor radio propagation at 40–60 Ghz

Factors that influence the accuracy of high frequency models for indoor radio propagation at 40–60 GHz are identified and discussed. Simulation results obtained on the basis of Geometrical Optics are presented. The reliability of these results is examined by comparing them with those obtained from empirical measurements.     

A Superconducting Tunnel Junction Receiver for 230 GHz

The performance of superconducting tunnel junctions as high-frequency receivers is discussed. Low-noise mixing in superconductor insulator-superconductor (SIS) quasi-particle tunnel junctions has been seen for frequencies up to 400 GHz. Such mixers have the significant advantage of small local-oscillator power requirements. A receiver has been constructed which has a single-sideband (SSB) receiver noise temperature of 305 K at 241 GHz.     

Scattering at Circular-to-Rectangular Waveguide Junctions

A formally exact solution is given for the problem of scattering at a circular-to-rectangular waveguide junction and at a thick diaphragm, with a centered circular aperture, in a rectangular waveguide. The method uses normal TE and TM mode expansions of the waveguide fields and traditional mode matching of the transverse electric and magnetic fields at the junction boundary. Exact closed-form expressions are obtained for the electric field mode-matching coefficients which couple the TE(TM) modes in the rectangular guide to the TE(TM) and TM(TE) modes in the circular guide. Numerical results are presented for the case of TE/sub 10/ mode propagation in the larger rectangular guide with all other modes cutoff. Convergent numerical results for the equivalent shunt susceptances of such junctions are obtained when about 12 modes (eight TE and four TM) are retained in the circular waveguide or in the circular aperture of the diaphragm. The results are graphically compared with formulas and curves due to the quasi-static theory of Bethe and the variational theory given in the Waveguide Handbook [2].     

Performance of GaAs MESFET Mixers at X Band

A theoretical analysis and experimental verification of the signal properties of the GaAs MESFET mixer are presented. Experimental techniques for evaluating some of the mixer parameters are described. Experiments performed on GaAs MESFET mixers at X band show that good noise performance and large dynamic range can be achieved with conversion gain. A conversion gain over 6 dB is measured at 7.8 GHz. Noise figures as low as 7.4 dB and output third-order intermodulation intercepts of +18 dBm have heen obtained at 8 GHz with a balanced MESFET mixer.     

双势垒隧道发光结的结构特点及其性能分析

成功地制备了Cu-Al2O3-MgF2-Au及Si-SiO2-Al-Al2O3-Au两种结构双势垒隧道发光结。由于双势垒结中第二栅存在着不同的分立能级,电子存在共振隧穿效应,使双势垒隧道结发光光谱的波长范围及谱峰位置比普通单势垒隧道结均向短波方向发生了移动。对双势垒隧道发光结的I-V特性测试表明,I-V曲线中存在着明显的负阻区,分析表明,负阻现象与电子的隧穿特性、表面等离极化激元(SPP)的激发及SPP的耦合发光之间相互关联。     

The Application of Superconducting Tunnel Junction Detectors to Astronomy

Detectors based on the superconducting-insulating-superconducting (SIS) junction long ago surpassed Schottky-diode semiconductor detectors as the most sensitive heterodyne mixers in the millimeter and submillimeter (far-infrared) wavelength range. Other novel superconducting device configurations have been applied as direct detectors. Though still in the early stages of development, and yet to find widespread application, they have demonstrated advantages over traditional semiconductor detectors in specialized situations. Exciting progress has been made in recent years in developing the superconducting tunnel junctions (STJ) as a photon detector for optical and near-optical wavelengths, where silicon CCD's are currently dominant. I examine some of the areas in which the properties of STJ detectors may best match the instrument capabilities that astronomical observations require, and discuss the implications of the intrinsic spectral resolution of the STJ. This capability will enable a significant increase in observing efficiency, once the technology matures, that should justify increased complexity of cryogenic systems, particularly for instruments to be used on the next generation of large ground-based telescopes.     

Superconducting lead cavities at 35 GHz

An investigation of machined superconducting lead cavities operating in the circular cylindrical TE011mode at 34.8 GHz is reported. Measured values of the surface resistance and the shift of the resonance frequency are presented and compared with calculated values. Construction criteria for high-Q cavities are proposed, based on a discussion of the different loss mechanisms in a cavity. According to these criteria 10 cavities were processed and investigated by Q measurements. The surfaces were examined by microscope. A new untraditional method for examining machined surfaces was applied. Recognizing that a surface with surface defects has both inferior electrical properties and decreased mechanical strength compared with a perfect surface, different surfaces were treated in ultrasonic baths in order to examine the mechanical strength. The degree of destruction of the surfaces was compared with the Q values of cavities with surfaces constructed in the same way.     

Determination of the Parameters of Tunneling Barriers of Superconducting Tunnel Structures for Submillimeter Receivers

Journal of Communications Technology and Electronics - Abstract—The parameters of the tunneling barrier of Nb/Al–AlOx/Nb Josephson junctions were estimated in a wide range of current...     

Prediction methods for rain attenuation statistics at variable path angles and carrier frequencies between 13 and 100 Ghz

Fade depth and space diversity statistics of propagation along earth-satellite paths have been calculated from radar reflectivity data of rain using modeling procedures. The reflectivity data base was obtained during the summer of 1973 at Wallops Island, Va., using a high resolutionSband radar interfaced with a computer and digital processing system. Fade statistics have been calculated for various path angles at several frequencies between 13 and 100 GHz. Subsequent analysis has demonstrated the ability to predict the following: 1) fade statistics at other path elevation angles given similar type statistics at a particular path angle, 2) space diversity statistics at other frequencies, given similar type statistics at a particular frequency, and 3) fade statistics at a third frequency given similar type statistics at two other frequencies. Although a specific data base was used pertaining to the climatology at Wallops Island, the techniques developed are general and may be applied to existing or future "fade measurements" at other climatological locations.     

Upgrading the Haystack radio telescope for operation at 115 GHz

The Haystack 37-m radio telescope has been upgraded for operation at frequencies up to 115 GHz. A unique deformable subreflector with active actuator control has been developed to correct for gravitational distortion effects including astigmatism and deflections associated with the particular reflector surface. Active thermal compensation of the surface has also been implemented to conduct for both thermal lag effects and circularly symmetric gravitational deviations. Holographic mapping of the antenna surface deviations was achieved using 12-GHz geostationary satellite transmissions, which required the use of special techniques to correct for diffraction and multiple reflection effects involving the space-frame radome that covers the antenna. Realignment of the antenna surface utilized a finite-element structural model to translate surface deviations to motions of the unusual adjustment mechanisms on the antenna. The currently measured rms surface deviation (Dec. 23, 1992) is 210 μm. The telescope has been equipped with a two-channel cryogenically cooled 3-mm SIS receiver, covering the range from 84 to 115 GHz. A new flexible digital spectrometer has been constructed for spectral line astronomy. Configurations can range from a widest bandwidth coverage of 160 MHz at 512 lags to 0.66 MHz at 4096 lags. Examples are given of surface holographic maps and radio measurements of aperture efficiency, pointing, and other performance parameters     

Effects of Trains on Cutoff Frequency and Field in Rectangular Tunnel As Waveguide

Effects of trains in a rectangular tunnel on the cutoff frequency and field were determined at the range of VHF, UHF, and SHF bands by the finite-element method. According to this study, the tunnel is a transmission channel of high-pass type waveguide. The tunnel and the trains were assumed to be infinitely long and fully conductive. Generally speaking, the trains in the tunnel lowered TE/sub nm/ wave cutoff frequencies and raised TM/sub nm/ cutoff frequencies. Closer monitoring, however, has shown that the above results may be reversed, depending on the conditions. The field is represented by contour lines. Thus, its change is clearly shown by a change in the distribution of the lines caused by the train in the tunnel. Although the train changed field distribution for both TE/sub nm/ and TM/sub nm/ mode, greater changes were usually observed in higher order mode fields.     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a ～1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (ωR_nC_j≈3, R_n≈70 Ω) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of ≥ 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit ?v/k～11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

Design and Performance of an Ultra-Narrowband Superconducting Filter at UHF Band

A stepped impedance spiral resonator suitable for high-temperature superconducting (HTS) filter with bandwidth narrower than 0.5% is presented. An eight-pole demonstration HTS filter is developed with a central frequency of 650 MHz and a bandwidth of 0.3%. The measurements show that the insertion loss is less than 0.3 dB, and the return loss is better than 16 dB. The filter has out-of-band rejections of 65 dB at 2 MHz below the passband and 80 dB at 2 MHz above the passband, respectively.     

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.     

A Superconducting Microstrip Ultra-Wideband (UWB) Bandpass Filter at VHF-Band

A compact superconducting ultra-wideband filter with a passband from 125 to 260 MHz is demonstrated. The filter consists of ten shunt short-circuited stubs separated by connecting lines. The short-circuited stubs are grounded via a grounding strip that is attached to the box wall by a number of SiAl bonding wires. The filter is realized on two 2 in YBCO/LaAlO₃ substrates, which are connected by two bonding wires. The measured results demonstrate an insertion loss of less than 0.08 dB and a return loss of better than 21 dB without tuning. Furthermore, the experimental results of the filter are in good agreement with the simulated ones.