Design of wideband circularly polarized aperture-coupled microstripantennas

Two variations of a novel feeding technique for a wideband circularly polarized aperture-coupled microstrip antenna are described. Prototype designs for wideband linearly polarized elements are first presented, and then used for circularly polarized designs. Techniques used for design of the feed network are detailed, for both series feed and parallel feed versions. Experimental results are shown for each antenna, and results for the two designs are compared. The impedance and axial ratio bandwidths for these antennas are among the best yet achieved for microstrip antenna elements. Several design variations are also discussed     

Maximum Likelihood Estimation of Label Imperfection Probabilities and Its Use in the Identification of Mislabeled Patterns

This paper presents the problem of estimating label imperfections and the use of the estimation in identifying mislabeled patterns. Expressions for the maximum likelihood estimates of classification errors and a priori probabilities are derived from the classification of a set of labeled and unlabeled patterns. Expressions also are presented for the asymptotic variances of probability of correct classification and proportions. Simple models are developed for imperfections in the labels and for classification errors and are used in the formulation of a maximum likelihood estimation scheme. Schemes are presented for the identification of mislabeled patterns in terms of thresholds on the discriminant functions for both two-class and multiclass cases. Expressions are derived for the probability that the imperfect label identifi'cation scheme will result in a wrong decision and are used in computing thresholds. Furthermore, the results of practical applications of these techniques in the processing of remotely sensed multispectral data are presented.     

Robust estimators of the 2-parameter gamma distribution

The available estimators for parameters of the gamma distribution are moment estimators, maximum-likelihood estimators, and approximations to the maximum-likelihood estimators. These estimators are not suitable for small samples; however, they are still being used at the present time. The proposed robust estimators for scale and shape parameters are more suitable for small samples. They have RMS (root-mean-square) errors that are considerably smaller than those of the other estimators. In addition, they are easier to calculate, and are therefore appropriate in many applications     

Throughput and packet error probability of cellularfrequency-hopped spread-spectrum radio networks

The authors characterize multiple-access interference for cellular mobile networks, in which users are assumed to be Poisson-distributed in the plane and use frequency-hopped spread-spectrum signaling with a transmitter-oriented assignment of frequency-hopping patterns. Exact expressions for the bit error probabilities are derived for binary coherently demodulated systems without coding. Approximations for the packet-error probability are derived for coherent and noncoherent systems and these approximations are applied when forward-error-control coding is used. In all cases, the effects of varying interference power are accurately taken into account according to some propagation law. Numerical results are given in terms of bit-error probability for the exact case and throughput for the approximate analyses. Comparisons are made with previously derived bounds, and it is shown that these tend to be very pessimistic     

Adaptive filters suitable for real-time spectral analysis

New cascade structures for adaptive filters are presented. They are especially suitable for real-time applications. Since the new structures are intended to be realized using single-chip DSP ICs or single-chip custom VLSI circuits, the requirements for memory and divisions are minimized. The new structures are based on state-variable biquads that in addition to having good SNRs and low sensitivities (for fixed-point implementations) can also have their resonant frequencies and Q-factors independently tuned. The special cases of using the adaptive filters for tracking sinusoids corrupted by noise and for formant based speech compression are described in detail.     

Detection of Modulated Gaussian Signals in Noise

A method using Hermite polynomials is utilized for analyzing the outputs of νth-law devices for inputs of modulated Gaussian signals and zero-mean Gaussian noise. New results are developed for the output correlation functions, and techniques for obtaining closed-form expressions are pointed out. Output signal-to-noise ratios for various input carrier-to-noise-power ratios are calculated, and plots are shown for a single sinusoidal modulating signal. Results are derived to show the existence of a theoretical maximum for the output signal-to-noise ratio. The method can be directly applied for the case of general Fourier expandable signals modulating a Gaussian carrier.     

Noise-figure calculations for crossed-field forward-wave amplifiers

The problem of finding an adequate model for derivation of noise-figure expressions for crossed-field forward-wave amplifiers is investigated. The modified Llewellyn-Peterson equations are used for the portion of the beam near the cathode. Four waves, two cyclotron waves and two space-charge waves, are used for the space connecting the gun and interaction region. Noise-figures are found by considering five waves in the interaction region. The results are very close to those found when only the space-charge waves are considered in the development of the equations for both drift and interaction regions. A matrix, like the space-charge-wave matrix for O-type beams, giving the transformation of beam fluctuations along a drifting, crossed-field stream including the effects of four waves is presented. Expressions for fluctuations of transverse velocity and beam center of gravity are derived to account for all the excitation quantities which are believed to be important in crossed-field amplifiers. The transformation of fluctuations of beam position, or center of gravity, along an accelerating stream is derived. Calculated values of noise figures are far in excess of experimental values. The reasons for the discrepancies are discussed.     

Dialogue-based user models

The paper investigates several approaches to user modeling in natural-language dialogue systems. First, reasons are pointed out why user modeling has become so important in the last few years, and definitions are proposed for the notions of "user model" and "user modeling component." Then, techniques for constructing user models in the course of a dialogue are presented and recent proposals for representing a wide range of assumptions about a user's beliefs and goals in a system's knowledge base are surveyed. Examples for the application of user models in systems developed to date are presented, and some social implications are discussed. Finally, unsolved problems like coping with collective beliefs or resource-limited processes are investigated, and prospects for application-oriented research are outlined.     

Phased Mission Analysis: A Review of New Developments and An Application

Both exact and approximate methods for obtaining the unreliability of a nonrepairable system undergoing a phased mission are presented. The techniques are applied to an emergency core cooling system for a boiling water reactor. The estimates for the example agree well with the exact solution. The accuracy and ease of implementation are compared for both methods. The approximation techniques for unavailability estimates for phased missions contained in this paper are useful for industrial applications. The techniques are implementable and existing computer programs such as MOCUS, PREP, and KITT can be used for the analysis although such use is not efficient at this time. These programs are currently being modified, for efficient use in phased mission problems, at the Idaho National Engineering Laboratory. MOCUS, PREP, and KITT are obtainable from the Argonne Code Center; 9700 South Cass Avenue; Argonne, IL 60439 USA.     

Frontal methods for the space-time processing of ultra-wideband signals in exploration seismology and ground penetrating radar

Methods for the space-time processing of ultra-wideband signals used in short-range and ground penetrating radar as well as exploration seismology for execution of migration transformation procedures are analyzed. Procedures for obtaining the geometricalal parameters (position, shape, and orientation) of reflecting boundaries and diffracting objects from signals recorded during scanning in some spatial zone are proposed. Different methods for the implementation of linear and nonlinear migration transformations are analyzed. Frontal migration transformation methods are analyzed in more detail and advantages of these methods are demonstrated. Interactive and computer-aided versions of such methods are presented. Analytical relationships for the implementation of these versions of the space-time signal processing are presented.     

近场头相关传输函数及其应用

综述了近场头相关传输函数(HRTF)及其应用问题,讨论了近场HRTF的测量、理论计算及其物理特征。最后讨论了近场HRTF在双耳听觉和消费电子领域的应用。     

红外图像的计算机仿真及仿真软件

根据红外成像理论,提出了红外图像计算机仿真的原理和方法,分析了各种辐射对成像的影响,给出了辐射计算公式及无源场景温度求解方法,说明了场景模型、大气传输模型和材料的物理特性库在红外图像仿真中的作用,介绍了一种红外图像计算机仿真软件,进行了仿真实验并给出了一些仿真图像。     

振荡器时变相位噪声分析技术研究进展

介绍了两种射频振荡器的时变相位噪声模型:Demir&Mehrotra的非线性扰动模型和Hajimiri&Lee的时变相位噪声模型。对一个简单的非线性电导LC振荡器,分别建立了这两种模型,并指出了两种模型的联系和区别。讨论了两种模型的计算方法,介绍了在EDA软件HSpice和SpectreRF下,以及频域中相位噪声的计算问题。最后,进一步讨论了时变相位噪声,指出相位噪声分析的难点和未来的发展方向。     

WARC's last act?

The upcoming 1992 World Administrative Radio Conference is discussed. The reasons for its importance are given, and three new types of services that are high on the list for consideration are examined. They are universal personal telecommunications, digital audio broadcasting, and high-definition satellite TV. US preparations for the conference and important international alliances are discussed     

MEMS惯性传感器可靠性试验方法研究

MEMS惯性传感器在军事与商业应用中的一个主要问题便是可靠性试验方法尚未标准化,因而目前绝大多数MEMS惯性传感器器件的可靠性试验依据的是傲电子的试验标准。但是,这些标准对于这类器件的适用性却受到许多机构的质疑,国外关于该问题的研究也已起步。汇总了MEMS惯性传感器器件的结构和工作原理等信息,重点总结了该类器件的典型环境失效机理,并将典型的环境载荷情况与失效机理进行了对比分析：从现有的微电子可靠性试验标准中选取了针对不同环境失效机理的试验方法。并对其适用性问题进行了讨论。     

光纤光缆现行标准概览

介绍了光纤光缆的最新IEC、ITU-T国际标准、国家标准和行业标准概况,并对部分内容作了必要的评述.文中同时对光缆用材料的标准状况进行了介绍.最后提出了我国标准制定工作中有待改进的建议.     

Efficient and accurate modeling of planar anisotropic microwavestructures by the method of lines

A new algorithm for the analysis of planar microwave structures with anisotropic substrates is proposed and substantiated. This algorithm is based on generalized transmission-line (GTL) equations, which are developed here for numerical algorithms. For the purpose of analysis, two different modal matrices for the discretized transverse electric and magnetic fields are calculated. Furthermore, impedance/admittance transformation formulas are developed with the help of the GTL equations for longitudinal sections and general junctions. Crossed discretization lines are used in the latter case. The materials are assumed to be biaxial or specific anisotropic. Special algorithms are developed for junctions consisting of more than two waveguides in the cross section and for bends. The proposed algorithm is verified by numerical results     

CAD models for asymmetrical, elliptical, cylindrical, andelliptical cone coplanar strip lines

By the conformal mapping method, we give analytical closed form expressions for the quasi-TEM parameters for asymmetrical coplanar strip lines (ACPSs) with finite boundary substrate. Then, based on the analysis of ACPSs, elliptical coplanar strip lines (ECPSs) and cylindrical coplanar strip lines (CCPSs), and elliptical cone coplanar strip lines (ECCPSs) are studied. Computer-aided-design oriented analytical closed-form expressions for the quasi-TEM parameters for ACPSs, ECPSs, CCPSs, and ECCPSs are obtained. All of the expressions are simple and accurate for microwave circuit designs and are useful for transmission-line theory and antenna theory. The reasonableness of the method and results are verified and various design curves are given     

Theory of two-photon measurement of laser output

Two-photon fluorescence and second-harmonic generation experiments have been used recently to study the picosecond structure of laser signals. A general theory of these measurements is presented in this work, which includes a detailed analysis of the possible responses of the measurement to a mode-locked laser that produces pulses and to a free-running laser that produces a noise-like output. Shapes Of the expected response patterns are calculated; second-order statistics that describe statistical departures from the expected patterns are also determined. Results are given for an arbitrary number of laser modes and general mode spectrum, in computationally useful forms for small and large mode number. Illustrative examples for large mode number are worked out for Gaussian and uniform mode profile curves; in addition, exact results are obtained for the uniform case of any (odd) number of modes. Sample response patterns for the case of a free-running laser are calculated by Monte-Carlo technique for Gaussian and uniform mode spectra. Results that reduce to special cases treated in various prior works are pointed out and new findings are discussed.     

R&D manpower forecasting for chemical industries in India

The results of a study conducted in India to determine the R&D manpower requirements toward the end of the century in for the country's chemical industries are presented. For 1981-1987 data, projections are made for short-term and long-term manpower requirements. To account for environmental changes, variable parameter regression is used for ten years and exponential smoothing is used for subsequent years. The explanatory variables for the manpower requirements are established and are partitioned into time-dependent and time-independent variables