A robust adaptive beamforming method is proposed to cancel coherent, as well as incoherent, interference using an array of arbitrary geometry. In this method, coherent interferences are suppressed by a transformation of received data with the estimates of their arrival angles and then, to reject incoherent interferences, the array output power is minimized subject to the look direction constraint in the transformed signal-plus-interference (TSI) subspace. This TSI subspace-based beamforming results in robustness to errors in the angle estimations. Its performance is theoretically examined. The theoretic results conform to simulation results. It is straightforward to apply the theoretic results to the performance analysis of subspace-based adaptive beamfomers only for incoherent interference cancellation.

In this letter, an algorithm that estimates one of the most important channel parameters, maximum Doppler frequency, fD, is proposed. The algorithm uses phase variations of received pilot signals, which is strongly related with fD in a fading environment. In addition, a phase variation measurement method for binary phase shift keying (BPSK) modulated signals is also proposed and it makes possible to estimate fD from BPSK modulated information signals as well as unmodulated pilot signals. The results show that the proposed algorithm is very simple and shows good performance over wide Doppler frequency range.

We report our studies on electrical current pulse perturbation of superconducting YBa2Cu3O7-x (YBCO) epitaxial thin films. When a current pulse is applied to a YBCO microbridge, a voltage develops across it that depends on the amplitude of the input current pulse. For a total current (input current pulse plus the dc bias) that is lower than the critical current Ic, an inductive voltage response is observed. When the total current exceeds Ic, a resistive response is generated and is observed after a certain delay time td. The origin of the resistive response was analyzed using the Geier and Schon model, which is based on the time-dependent Ginzburg-Landau equation. Our experimental samples consisted of 200-nm-thick epitaxial YBCO films, patterned into coplanar-strip (CPS) transmission lines, containing either two-microbridge or single-microbridge test structures. For the two-microbridge samples, a train of 100-fs-duration optical pulses was used to excite the larger microbridge and generate 2-ps-duration electrical pulses, which were then applied to perturb the smaller microbridge, which was independently biased in the superconducting state. In this case, an electro-optic sampling system was used to measure the YBCO kinetic-inductive voltage responses with the picosecond time resolution. For the single-microbridge structures, an electronic pulse generator was employed to supply the input current pulse, and a 14-GHz sampling oscilloscope was used to monitor the microbridge responses. The latter signals were in very good agreement with the model of Geier and Schon, assuming that the quasiparticle dynamics process that resulted from the nanosecond-wide current excitation was bolometric and followed the phonon escape time τes.

Almost all land animals coordinate their behavior with circadian rhythms, matching their functions to the daily cycles of lightness and darkness that result from the rotation of the earth corresponding to 24 hours. Through external stimuli, such as dairy life activities or other sources from our environment may influence the internal rhythmicity of sleep and waking properties. However, the rhythms are regulated to keep their activity constant by homeostasis while fluctuating by incessant influences of external forces. A modeling study has been developed to identify homeostatic dynamics properties underlying a circadian rhythm activity of Sleep and Wake data measured from normal subjects, using an MA (Moving Average) model associated with Backpropagation (BP) algorithm. As results, we found that the neural network can capture the regularity and irregularity components included in the data. The order of MA neural network model depends on subjects behavior, the first two orders are usually dominant in the case of no strong external forces. The adaptive dynamic changes are evaluated by the change of weight vectors, a kind of internal representation of the trained network. The dynamic is kept in a steady state for more than 20 days at most. Identified properties reflect the subject's behavior, and hence may be useful for medical diagnoses of disorders related to circadian rhythms.

High-Tc superconductors convincingly showed that these materials are essentially natural arrays of Josephson junctions formed in atomic scale. In this paper, in-plane aligned a-axis-oriented YBa2Cu3O7-δ (YBCO) thin films were successfully grown on LaSrGaO4(LSGO) (100) substrates which were cleaned by ion-beam. Voltage jumps with hysteresis implying intrinsic Josephson effects are observed in c-axis direction. This result suggest that it is possible to achieve planar intrinsic Josephson devices which have applications in high frequency electronics, such as voltage standards, Josephson masers and so on.

Lymph-node detection system using a high Tc SQUID and ultra-small particles was proposed. Pseudo lymph nodes containing small iron particles were made and the magnetic signal was measured. The SQUID signal was proportional to the weight of the iron in the fluid. At the distance of 20 mm, the detectable minimum weight of the iron was 40 µg. We demonstrated that the possibility of the application of the system to the human body.

A new method is proposed for determining the parasitic extrinsic resistances of MESFETs and HEMTs from the measured S-parameters under active bias. The proposed method is based on the fact that the difference between drain resistance (Rd) and source resistance (Rs) can be found from the measured S-parameters under zero bias condition. It is possible to define the new internal device including intrinsic device and three extrinsic resistances by eliminating the parasitic imaginary terms. Three resistances can be calculated easily via the presented explicit three equations, which are induced from the fact that 1) the real parts of Yint,11 and Yint,12 of intrinsic Y-parameters are very small or almost zero, 2) the transformation relations between S-, Z-, and Y-matrices. The modelled S-parameters calculated by the obtained resistances and all the other equivalent circuit parameters are in good agreement with the measured S-parameters up to 40 GHz.

Two novel linearization processes in electro-absorption-modulator (EAM) are proposed and demonstrated. These two modulation schemes are used to compensate the nonlinear component of the EAM by controlling the DC bias voltages of the each EAM separately. The simulations on the nonlinearity of EAM and linearization process are performed in both time and frequency domains. From a serially cascaded modulation simulation, a reduction of 16 dB in IMD3, 45 dB in IMD5 and the following increase of 15 dB in linear dynamic rage (LDR) are achieved. In dual-parallel modulation experiment at 8 GHz, a reduction of 23 dB in IMD3 and the following increase of 15.1 dB in LDR of are achieved compared to those of a single EAM operation.

This letter presents a low spurious frequency setting algorithm for a triple tuned type PLL synthesizer driven by a DDS. The triple tuned PLL synthesizer is based on a single PLL configuration with two variable frequency dividers. The DDS is employed for a reference source of the PLL. The proposed algorithm determines appropriate frequency tuning values of the DDS frequency and the division ratios of two frequency dividers. The division ratios are selected to achieve a desired output frequency while the low spurious condition of the DDS has been maintained. A 5 to 10 GHz synthesizer with frequency step of 500 kHz demonstrated spurious level below -46 dBc with improvement of 13 dB.

We present measurements of kilohertz and megahertz sine waves synthesized using a Josephson arbitrary waveform synthesizer. A 4.8 kHz sine wave synthesized using an ac-coupled bias technique is shown to have a stable 121 mV peak voltage and harmonic distortion 101 dB below the fundamental (-101 dBc (carrier)). We also present results of our first phase-noise measurement. A 5.0 MHz sine wave was found to have distortion 33 dB lower than the same signal synthesized using a semiconductor digital code generator. The white-noise floor of the Josephson synthesized signal is -132 dBc/Hz and is limited by the noise floor of the preamplifier.

The non-linear quasiparticle tunnel current flowing in a distributed superconductor-insulator-superconductor (SIS) transmission line resonator has been exploited in a low-noise heterodyne fixed-tuned waveguide receiver in the 600-700 GHz band. The mixer employs two half-wave or full-wave distributed SIS long junctions connected in series. These devices have been fabricated with optical lithography. At 654 GHz, a Y-factor of 1.79 has been recorded, corresponding to a double-side-band (DSB) receiver noise temperature of 198 K at an IF of 3 GHz.

We describe here development of a multichannel high-Tc SQUID magnetometer system for measurement of cardiac magnetic fields, aiming at future application of diagnosis of heart diseases. Two types of direct-coupled SQUID magnetometers were fabricated and used: single pickup coil magnetometer having flux dams to suppress the shielding current that would induce flux penetration and the consequent low-frequency noise, and double pickup coil magnetometer having no grain boundary junctions and flux dams on the pickup coil. The superconducting film of both the magnetometers had holes and slots, leaving 5 µm-wide strip lines, to suppress trapping and penetration of magnetic flux vortices in environmental fields. We studied different schemes of active shielding to reinforce the efficiency of field-attenuation of magnetically shielded room (MSR). A feedback-type compensation using a normal detection coil wound around the wall of MSR and a selective cancellation of 50 Hz noise by means of adaptive filter were developed. Such combination of passive and active shielding, based on the use of simple MSR, would be suitable in a practical low-cost magnetometer system for clinical MCG examination. We fabricated a liquid nitrogen cryostat that could contain up to 20 magnetometer-capsules at 4 cm separation in a flat bottom, with a distance of 16 mm between the air and liquid nitrogen. The cryostat was set in a gantry, which had rotational, vertical and horizontal freedoms of movement, in a moderate-shielding MSR that was combined with the developed active shielding. Measurements of MCG were performed for normal subject using eight magnetometers operating simultaneously.

Thermally activated magnetic-flux entry into a pickup coil through a flux dam in high Tc superconducting quantum interference device (SQUID) is studied. The behavior of this thermal activation is analyzed in terms of the circulating current flowing in the pickup coil. It is shown that the thermal activation can be prevented when the circulating current becomes much below a critical current of the flux dam. It is also shown that we need a long waiting time in order to realize this situation since the circulating current logarithmically decays with time in the case of the thermal activation. The relationship between the thermal activation and the circulating current is qualitatively confirmed with the experiment. We also show a method in order to forcibly reduce the circulating current instead of the thermal activation. In this case, we can prevent the thermal activation without the long waiting time.

We have developed and demonstrated a novel technique for electrical inspection and electrical failure analysis, which can detect open, high-resistance, and short circuits without the need for electrical contact with the outside of the LSI chip or the board on which the LSI chip is mounted. The basic idea of the technique is the detection of the magnetic field produced by OBIC (optical beam induced current) or photo current. A DC-SQUID (superconducting quantum interference device) magnetometer is used to detect the magnetic field. This scanning laser-SQUID microscopy ("laser-SQUID" for short) has a spatial resolution of about 1.3 µm. It can be used to distinguish defective chips before bonding pad patterning or after bonding without pin-selection. It can localize any defective site in the chip to within a few square microns.

We have developed a new torque magnetometer on the basis of a 4-K refrigerator. The system temperature can be lowered down to 1.5 K by pumping liquefied helium from a top loading sample space. A piezoresistor bridge on a Si cantilever is used to detect torque acting on a sample. A transverse magnetic field is supplied by a variable-field permanent magnet up to 10 kG. We find that a sensitivity of our torque magnetometer is Δ τ 10-10 Nm.

We have designed a torque magnetometer using a 60-kG split-type superconducting magnet. A balance torque compensates the torque acting on a sample in the magnetic field. The feedback circuit for a sample direction consists of an optical position sensor, a moving coil, and a PID controller. We measured the coil current to know a sample torque. The whole torque machinery is directly rotated by a stepping motor of angular resolution 0.0036. An advantage of the torque apparatus is a wide dynamic range up to 1000 dyncm. The sample temperature can be controlled between 4 K and 300 K.

We present the design of dual rail Data Driven Self Timed (DDST) DEMUX and MUX circuits for 50 GHz operation. The chosen current density is 6.5 kA/cm2 and simulations show good margins for speeds exceeding 50 GHz. Our previously reported dual-rail on-chip test system is also scaled up for 50 GHz operation.

This article addresses the problem of designing and implementing multigigabit post-detection filters for application in optical communication systems using optical soliton pulses. The designed filters have the main advantages of full integration, electrically adjustable frequency response and active input and output impedance match.

With the emerging technology of photonic networks, careful design becomes necessary to make most of the already installed fibre capacity. Appropriate numerical tools are readily available. Usually, these are based on the split-step Fourier method (SSFM), employing the fast Fourier transform (FFT). With N discretization points, the complexity of the SSFM is O(N log2N). For real-world wavelength division multiplexing (WDM) systems, the simulation time can be of the order of days, so any speed improvement would be most welcome. We show that the SSFM is a special case of the so-called collocation method with harmonic basis functions. However, for modelling nonlinear optical waveguides, various other basis function systems offer significant advantages. For calculating the propagation of single soliton-like impulses, a problem-adapted Gauss-Hermite basis leads to a strongly reduced computation time compared to the SSFM . Further, using a basis function system constructed from a scaling function, which generates a compactly supported wavelet, we developed a new and flexible split-step wavelet collocation method (SSWCM). This technique is independent of the propagating impulse shapes, and provides a complexity of the order O(N) for a fixed accuracy. For a typical modelling situation with up to 64 WDM channels, the SSWCM leads to significantly shorter computation times than the standard SSFM.

A flash analog-to-digital converter (ADC) that uses resonant-tunneling complex gates is proposed. The ternary quantizers, consisting of monostable-to-multistable transition logic (MML) circuits, convert the analog input signal into the ternary thermometer code. This code is then converted into the binary Gray-code output by a multiple-valued multiple-input monostable-bistable transition logic element (M2-MOBILE). By assuming InP-based resonant-tunneling diode (RTD) and heterojunction field-effect transistor technology, we have carried out SPICE simulation that demonstrates a 4-bit, 10-GS/s ADC operation. The input bandwidth, defined as a frequency at which the effective number of bit decreases by 0.5 LSB, was also estimated to be 500 MHz. Compact circuit configuration, which is due to the combination of MML and M2-MOBILE, reduces the device count and power dissipation by a factor of two compared with previous RTD-based ADCs.