Fitting of measured data to a known relationship

A computer program is described which calculates the `constants? of a known relationship between two variables. Measured values of the variables are supplied and up to four `constants? may be evaluated if their approximate values are known.     

Equivalent-step-index parameters for single-mode fibres having a power-law profile

An approach using three transformation coefficients to derive the equivalent-step-index parameters is described. Compared with those obtained using two transformation coefficients, improved predictions of transmission characteristics may be achieved. This is illustrated by examples involving power-law profiles.     

Blind identifiability of a quadratic stochastic system

Quadratic systems appear in various fields of signal processing, in particular in detection and estimation. In this paper, we establish some conditions to determine the order and identify the coefficients of any discrete and finite extent quadratic system driven by a sequence of independent and identically distributed random variables. The input sequence is assumed unobservable and the conditions are based on some properties of the output cumulant functions up to the third order. Necessary and sufficient conditions ensuring the determination of the order are given. A sufficient condition of uniqueness to recover the parameters is presented. Lastly, some examples are given     

Goodness-of-fit and local identifiability of a receptor-bindingradio-pharmacokinetic system

A four-state nonlinear model describing a radiopharmacokinetic system for a hepatic receptor-binding radiopharmaceutical, [99mTc]-galactosyl-neoglycoalbumin (TcNGA), was tested for goodness-of-fit and local identifiability using scanning data from nine healthy subjects and seven patients with severe liver disease. Based on standard deviations of liver and heart imaging data at equilibria as a measure of observational error, the reduced chi-square ranged from 0.5 to 2.6. Values above 1.2 occurred when the subject moved during the 30 min study. Relative standard errors for each parameter were: TcNGA-receptor forward binding rate constant kb, 13-54%; extra-hepatic plasma volume Ve, 0.8-15.0%; hepatic plasma volume Vh, 0.2-6.5%; hepatic plasma flow F, 54----greater than 1000%; and receptor concentration [R]o, 0.3-13%. The highest standard errors occurred when the amount of TcNGA injected exceeded the total amount of receptor. Therefore, when TcNGA functional imaging was performed without excess patient motion and receptor saturation, the kinetic model provided data fits of low systematic error and yielded high precision estimates of receptor concentration and forward binding rate constant. In summary, optimal performance of the kinetic model occurred when the amount of injected TcNGA resulted in the nonlinear operation of the pharmacokinetic system.     

Design parameters and measured performance of the IRAM 30-mMillimeter Radio Telescope

The “Millimeter Radio Telescope” (MRT) is operated by the Institute for Radio Astronomy in the millimeter range (IRAM) and is located at 2850-m altitude in the Sierra Nevada, near Granada, Spain. It is a reflector antenna of 30-m diameter with a surface accuracy of 0.08 mm and a pointing accuracy of better than 2 arcsec. The telescope is equipped with sensitive receivers for the atmospheric windows between 0.8- and 7-mm wavelength. The authors describe the optics layout of the receiver and calibration system, which allows simultaneous observations at a number of frequencies. The special design aspects of the antenna, in particular the control of thermal deformations and the achievement of a high reflector and pointing accuracy are described. The authors compare the design computations with the characteristics of the telescope, derived from several years of operation and optimization. The success of the design is demonstrated by observational experience. The authors conclude the paper with a short review of some of the astronomical results obtained with the telescope     

An improved method to estimate intrinsic small signal parameters of a GaAs MESFET from measured dc characteristics

This investigation offers a technique to predict the ac behavior of mm wavelength GaAs metal semiconductor field effect transistors by using dc characteristics. To predict the intrinsic equivalent circuit parameters of the device from dc data, the measured dc characteristics are first simulated by employing a nonlinear dc model. The effects of biasing on the device ac parameters are evaluated for its low-noise applications. An improvement greater than 10% in predicting the ac response of the device is observed. The concept of depletion layer modification caused by the transverse electric field inside the channel is introduced for accurate Miller's capacitor modeling. It is assumed that with increased device biasing there are more unbalanced positive charges in the gate depletion toward the drain-side of the Schottky barrier. The electric field lines originated by these uncompensated charges induce an opposite charge density in the gate electrode. This modifies the gate biasing and hence the Schottky barrier depletion. As a result, the values of intrinsic ac device parameters change. It is observed that an accurate dc modeling is key to predicting an accurate ac small signal equivalent circuit of a device.     

The influence of a digital spectrum analyzer on the uncertainty in 1/f noise parameters

When noise is used as a diagnostic tool to determine the reliability of a device, not only the noise parameters itself, but also the uncertainty in these noise parameters are important. For good devices, this uncertainty will be Gaussian. However, because of non-linear measurement errors caused by a digital spectrum analyzer, this uncertainty might deviate from Gaussianity. We have estimated this additional error through simulations. We conclude that this error can often be ignored.     

Analysis of the electrical characteristics of power LDMOSFETs having different design parameters under various temperature

In this paper, we have investigated the electrical characteristics of power lateral double-diffused MOSFETs (LDMOSFETs) having different gate lengths (2.1–3 μm) and drift lengths (6.6–12.6 μm) in the temperature range 100–500 K. The results of this study indicate that gate length and drift region length have a great effect on electrical characteristics, but they have little effect on temperature dependence. The specific on-resistance and the off-state breakdown voltage increase with temperature. The result shows that the specific on-resistance increases exponentially with the exponent 2.2 and, by contrast, the off-state breakdown voltage increases linearly with a slope of 100 mV/K (drift region concentration of measured device: 2×10¹⁵ cm⁻³). As a result, R_on/BV, known for a figure of merit of power device, increases with temperature.     

Blind identifiability of a channel transfer function from thecorrelation and conjugate correlation functions of a fractionallysampled signal

The problem of blind identifiability of a digital communication channel using second-order statistics of the received signal is addressed. A time series representation of the fractionally sampled digital signal is used to obtain a novel, necessary and sufficient condition for blind channel identification from the correlation and the conjugate correlation functions of the corresponding vector stationary process     

Quantization of a signal having multiple hypotheses

This letter extends some earlier work by Max [1] on signal quantization to an input signal which may belong to one of several possible signal models. An optimum quantizer is derived and an example presented for illustration.     

A simple method to estimate the dispersion of silica optical fiber having unknown refractive index profile parameters

A new method to approximately determine the dispersion of the silica optical fiber with unknown refractive index profile parameters is presented. The estimated error in dispersion was about 12% and 7% for the double-core optical fiber and the conventional single-mode fiber, respectively.     

Design of a plasma torch having a flame of oblong cross-section

A novel design of plasma torch is described, in which the flame cross-section has a major axis five times that of the minor axis. The ion number density has been measured and compared with that of the conventional torch with a flame of circular cross-section.     

Robust detection of a known signal in nearly Gaussian noise

A detector that is not nonparametric, but that nevertheless performs well over a broad class of noise distributions is termed a robust detector. One possible way to obtain a certain degree of robustness or stability is to look for a min-max solution. For the problem of detecting a signal of known form in additive, nearly Gaussian noise, the solution to the min-max problem is obtained when the signal amplitude is known and the nearly Gaussian noise is specified by a mixture model. The solution takes the form of a correlator-limiter detector. For a constant signal, the correlator-limiter detector reduces to a limiter detector, which is shown to be robust in terms of power and false alarm. By adding a symmetry constraint to the nearly normal noise and formulating the problem as one of local detection, the limiter-correlator is obtained as the local min-max solution. The limiter-correlator is shown to be robust in terms of asymptotic relative efficiency (ARE). For a pulse train of unknown phase, a limiter-envelope sum detector is also shown to be robust in terms of ARE.     

Comparison of theoretical and measured P1dB of a photonic microwave link: influence of some physical parameters of the DFB laser

This paper studies a microwave photonic link built as an IM/DD or intensity modulation–direct detection semiconductor laser system. The radiofrequency gain and 1 dB compression point of the link are both simulated with a modelling approach and compared to measurements. The electrical model of the electro-optic transducer, a distributed feedback laser, is first presented. Taking into account the nonlinearities and noise sources, it is developed on the commercial electrical software Advanced Design System. Owing to this accurate model, the impact of the relaxation oscillation frequency is presented on the system nonlinearity characteristic as for example the input 1 dB compression point. The comparison of simulated results to measured ones confirms the accuracy of this model.     

Leakage characteristics of groove guide having a conductor strip

A full-wave characterization of the groove guide having a conductor strip is made based on the mode-matching procedure. All of the constituents of the structure, including a coupling strip, grooves and a radiating open end, are treated in a concise and rigorous way by using the generalized scattering matrix technique. Numerical results show that a set of channel guide leaky modes is also present in this structure in addition to the groove guide leaky mode. The complex propagation behaviors of both the groove guide leaky mode and the channel guide leaky mode are illustrated for various waveguide geometric parameters, and some conclusions regarding the design of leaky wave antennas using this structure are drawn     

Comparison of known signal detection schemes under a weaklydependent noise model

The authors consider the discrete-time signal detection problem under the presence of additive noise exhibiting weak dependence. They first propose a weakly dependent noise model, in which the additive noise is modelled as a moving average process. They derive the locally optimum, memoryless, and one-memory detector test statistics under the model. The asymptotic performance of the one-memory detector is compared with that of the locally optimum and memoryless detectors. Specific examples for the asymptotic performance comparison of these detectors are considered. The authors also investigate the finite sample-size performance of several detectors through Monte-Carlo simulation. It is observed that the one-memory detector can achieve almost optimum performance at the expense of only one memory unit under the weakly dependent noise model, and is rather insensitive to slight model change     

Improving radiation-pattern distortion of a patch antenna having a finite ground plane

This paper presents a very useful and yet simple method of improving the radiation-pattern distortion of a patch antenna having a finite ground plane. The improvement can be achieved by cutting out the edges of the finite ground plane. This produces a phase shift between the induced equivalent magnetic currents on the edges, thereby causing cancellation in the diffracted fields. We numerically and experimentally examined the effects for some typical patch antennas and confirmed that the ripples in the copolar E plane pattern could be eliminated by using this approach.     

Design and manufacture of a microwave low-noise transistor having beam-leads

The design and fabrication technology of a bipolar microwave low-noise transistor with a beam-lead structure is described. The process which we present here has the following advantages: it is simple, it results in a satisfactory device reliability (Ti-Pt-Au metallizations and final passivation by a Si3N4layer), and it can be applied to the finest geometrical structures produced at the present time. The comparison between the results obtained for transistors in the beam-lead configuration and those obtained for packaged transistors clearly shows that microwave transistors can be fabricated with beam-leads with no degradation of the high-frequency performance. For a beam-lead interdigitated structure having four emitters 1.5 µm in width, the performance at 2 GHz was typically:G_{pmax} = 11.2dBN.F._{min} = 3.30dBG_{p}(N.F._{min}) = 9.2dB.