On the radiation pattern of a cornor reflector finite in width

Radiation pattern and gain of a corner reflector antenna finite in width are calculated by means of geometrical method for diffraction. The functionsF(T)sreferred to diffraction by the edges and their images are introduced. In the case of an aperture angle not equal to2pi /m(m: integer) a finite number of images of a dipole are considered, and the waves diffracted by the apex edge are introduced. The cases of aperture angles90deg,45degand115degare computed. The results are compared with the measured results obtained by Cottony and Wilson. In the forward and lateral directions agreements between both results are very good; however, in the rear direction it may be necessary to take into account the effects of the waves diffracted by the upper and lower edges of the reflector, when the length of the corner reflector is not too great.     

全反射镜结构对AlGaInP发光二极管发光效率的影响

采用计算机模拟的方法,计算了SiO2/Al,ITO/Al,SiO2/Au和ITO/Au全方位反射镜结构和分布式布拉格反射镜的反射特性.用PECVD和溅射设备制作了Glass/SiO2/Au结构,用LP-MOCVD生长了DBR结构,并测量了其反射特性,实验与模拟结果基本吻合.从模拟和实验的结果得到,SiO2/Au ODR结构在波长为630nm的垂直入射光下反射率很高,达到91%以上.对于不同角度的入射光,SiO2/Au在20°～85°都有很高的反射率,远高于DBR结构的反射率.在实际器件测试中,ODR结构的AlGaInP红光LED比无DBR结构的LED提高了115%,比DBR结构的LED提高了28%.这说明,ODR结构与DBR结构相比可以大幅提高红光LED的出光效率.     

Unpinning the GaAs Fermi level with thin heavily doped siliconoverlayers

A theoretical investigation is made into the unpinning of the GaAs Fermi level (E_f) at Schottky contacts by thin interfacial layers of heavily doped Si. The pinning mechanism is assumed to be a plane of interface states in the GaAs. The method used is to solve Poisson's equation numerically as a two-point boundary problem across the semiconductor. The results show that E_f can be moved from its pinned position to near the edge of the silicon valence band maximum or conduction band minimum at the Si/GaAs heterojunction with heavily doped p-Si or n-Si overlayers, respectively. This unpinning is observed with and without thick metallization on the Si. Exactly analogous results are obtained for Ge interfacial layers. The results are in good agreement with the experimental results obtained by J.R. Waldrop and R.W. Grant (1988). Although the unpinning is seen to occur for interface-state densities sufficient to pin E_f at the free GaAs surface, interface-state densities high enough to result in significant E_f pinning at metal/GaAs contacts are seen to prevent such unpinning by Si interfacial layers. It is therefore suggested that Si (or Ge) deposition gives rise to fewer interface states in the GaAs than does metal deposition     

Facet reflectivity and low-frequency noise in the light output ofLED and superradiant diodes

The influence of the reflection coefficient of cleaved facets from a double heterostructure laser on the l/f noise in light output is investigated. The experimental noise results are obtained by partially embedding the laser in Canada balsam, resulting in a decrease of the reflection coefficient, and by evaporating an aluminum coating, which results in a fully reflecting facet. These experimental results are shown to be in full agreement with an extension of existing models proposed by Fronen and Vandamme (l988). The 1/f noise arising from fluctuations in the refractive index is calculated, and it is concluded that this noise is negligible compared to the bulk noise in semiconductor lasers     

A millimeter-wave omnidirectional dielectric rod metallic gratingantenna

A new millimeter-wave omnidirectional dielectric rod metallic grating antenna is investigated theoretically and experimentally, in this paper. The radiation characteristics of the antenna are carefully investigated by a rigorous formulation for the TE₀₁-mode and TM₀₁-mode excitation in the Ka-band frequency range. Based on the analysis, an omnidirectional antenna excited by the TE₀₁ mode is designed and measured. The measured results are compared with theoretical predictions and good agreement is found. Extensive numerical results are given to establish some useful guidelines for the design of the omnidirectional antenna     

On the threshold setting principles in code acquisition of DS-SSsignals

This paper compares the meaning of different threshold setting principles in the code acquisition process of a direct sequence (DS) spread spectrum (SS) receiver. The consideration is made mainly in one-path additive white Gaussian noise (AWGN) channel. A consideration to a fixed multipath channel is given to see its effect on the results. Also, a consideration for a certain type of fading is given in a case where the signal power is assumed to be considerably lower, i.e., faded, part of the time. For the possible performance measures of code acquisition, the main interest is in the mean acquisition time T_MA . The probability of the acquisition in a given observation interval P_acq is also considered to see if different measures have different demands. A matched filter (MF) acquisition is used with and without a verification mode using an active integration. In the comparisons, fixed thresholds, thresholds based on constant false alarm rate (CFAR) criteria, and optimal thresholds in the sense to give either the minimum T_MA or the maximum P_acq are used. The results, which are obtained by using a method of selecting the maximum value at the output of the MF, are compared to the threshold cases. The results can be summarized as follows: when the performance measure is T _MA, the best results are obtained by using CFAR-based threshold comparison. By a proper selection of the probability of a false alarm, the same performance is obtained as by using the optimal thresholds. When the performance measure is P_acq, the maximum-selection method is the best choice     

Analysis of Wide-Band Stripline Circulators by Integral Equation Technique

The analysis of wide-band Y-junction stripline circulators using Green's function method was reported in the literature. In this paper, similar analyses are performed using an integral equation method and the results are compared. The boundary conditions used in the analyses are also discussed. A new boundary condition representing the actual fields more precisely than previously is formulated and applied to the junction. The results obtained with the new boundary conditions are examined and compared with the previous theoretical and experimental results. The current and voltage distributions that are created at the ports under the assumed boundary conditions are calculated and compared with the known stripline and junction modes. In the formulation, it is observed that the Green's function is not unique and it can be selected from a certain class of functions. This arbitrariness is introduced into the formulation by means of a complex parameter C/sub 0/. The effect of this parameter on the numerical results is investigated and it is shown that in certain regions of the complex C/sub 0/ plane, the numerical results converge on the analytical results.     

Transmitter linearity considerations for digital TV broadcasting

An introduction is given to the principles of digital modulation as it is being applied to advanced television by comparison with the way in which chrominance information modulates the NTC color subcarrier. The concept of the unit circle in constellation diagrams is explained for both signal-to-noise ratio and signal-to-interference. Using constellation diagrams, the effects of AM/AM and AM/PM and their combined effects are shown in terms of reducing noise/interference margins. it is seen that the dynamic range of the ATV transmitter must be sufficient to handle the transient peak power which results from filtering to constrain the data to the 6-MHz channel. Out-of-channel spectral components are generated by intermodulation in the high-power amplifier, as are in-channel intermodulation components which are responsible for reducing the eye opening. This results in reduction in noise/interference margins. It is shown that nonlinear amplification of the transient peaks results in intermodulation products that may cause interference to a signal on adjacent channels and reduce expected coverage     

Analysis and characterization of P-N junction diode switching

A new charge control model of a p-n junction diode is introduced in which the reverse current iRas well as the forward current IFare related to the chargeQstored in the base region by time constants τRand τF, respectively. The reverse switching transient is analyzed for normal switching operation where a constant current phase (storage phase) and a decaying current phase exist, and for overdriven switching operation where no constant current phase exists. New switching time equations are derived. The equations are expressed in terms of measurable device parameters τF, τR, and Cjexternal circuit variables IFand IRand an external circuit parameter R. The proposed model is applicable to p-n junction diodes of any type. Experimental results using various types of diodes are also reported. It is shown that the experimental results are in very good agreement with the theory.     

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.     

The visibility of noise in System I PAL colour television

The results of new subjective tests on the visibility of noise in System I PAL colour television are reported. Three forms of noise are considered: white (flat) noise, de-emphasised triangular noise, and the noise resulting from vestigial sideband demodulation (VSB noise). The results are compared with those given by work published 20 years ago and it is concluded that observers today are more critical of noise in pictures: about 2¹/₂ dB less noise is required to produce the same impairment     

Further comments on the design of log-periodic dipole antennas

The design procedure for the log-periodic dipole (LPD) antenna is discussed, by extending the results presented in a previous paper by the authors. The results of gain calculations, already published, are summarized and extended to cases of very thick dipoles. The gain analysis is completed with a discussion of the optimum antenna input feed lineZ_{0}'the achievable VSWR, the voltage gradient, and the effects of the presence of the ground. All the results of calculations given here are presented as a function ofZ_{0}(the characteristic impedance of the transmission line feeder),h/a(the ratio between the half-length and the radius of the dipoles),tau(the logarithmic decrement of the geometrical configuration), andsigma(the spacing ratio of dipoles), i.e., the parameters, which usually describe the geometry of an LPD array. The results of calculations are presented in many diagrams, for different values oftau,sigma, Z_{0}andh/a, which can be useful for accurate design of LPD antennas including those for high-power applications. Measurements of VSWR performed on antenna models have confirmed the computed results.     

Pyrex玻璃的湿法刻蚀研究

对Pyrex 7740玻璃的湿法刻蚀工艺进行了研究。实验中采用了几种不同的材料(光刻胶、Cr／Au、TiW／Au)作为刻蚀玻璃的掩膜，通过实验发现TiW／Au掩膜相对目前比较常用的Cr／Au掩膜有很多优点，如减少了玻璃的横向腐蚀，增加了深宽比，刻蚀图形边缘更加平滑等。还研究了腐蚀液成分配比对刻蚀结果的影响，发现刻蚀速率随HF浓度的增加而增加，且在HF浓度一定时，加入少量HNO3可以明显提高刻蚀速率。本文的实验结果对一些MEMS器件特别是微流体器件的制作有一定参考作用。     

Dual-frequency circularly polarised annular-ring microstrip antenna

The design of the circular polarisation (CP) for an annular-ring antenna operated at its TM/sub 11/ and TM/sub 12/ modes is presented. The CP radiations of the proposed design are achieved by placing an L-shaped strip connected to two orthogonal sides of the inner boundary of the annular patch. The dual-frequency CP operations are excited by a single probe-feed, and no additional 90/spl deg/ phase shifter and impedance-transformer circuit are required. A prototype of the proposed design was implemented and measured. Measured results show that broadside radiation patterns with good CP characteristics are obtained at the two operating resonant modes. Agreement between measured and numerical results is satisfactory.     

Arctic-wide operational sea ice drift from enhanced-resolution QuikScat/SeaWinds scatterometry and its validation

The near-real-time enhanced-resolution QuikScat/SeaWinds (QS) scatterometry composite data are used for daily automatic 48-h sea ice tracking by maximum cross-correlation over the entire Arctic. A correlation window of 61 /spl times/ 61 pixels is used for best performance. Both QS polarizations, vertical (VV) and horizontal (HH), are used independently, which permits to filter the final results for erroneous vectors by comparing the two drift vectors, u/spl I.oarr//sub VV/ and u/spl I.oarr//sub HH/, respectively. Additional filtering is performed by setting a minimum correlation coefficient and by considering the spatial consistency of the motion field. The algorithm has been validated with winter 2002/2003 buoy data from the International Arctic Buoy Program showing error standard deviations in the 48-h displacement of 3.1 and 3.2 km in the latitude and longitude direction, respectively. This corresponds to an error standard deviation in ice drift speed of just 2.6 cm/s. Errors are largest in dynamic regions with lower ice concentrations as for example the southern Fram Strait. The enhanced-resolution data improve previous drift results by about 25%, but are still blurred by the necessary 36-h period to produce the composites.     

Coupled mode theory of parallel waveguides

A new coupled mode formulation for parallel dielectric waveguides is described. The results apply to any guided modes (TE, TM, or hybrid) in waveguides of arbitrary cross-section, dissimilar index, and nonidentical shape. Additional index perturbations not included within the waveguides are encompassed by the theory. Propagation constants and mode patterns for the coupled modes computed according to this theory are shown to agree very well with numerical solutions for the system modes when the latter can be determined. Moreover, the new results are more accurate than those obtained from prior coupled mode formulations. It is shown that even for Iossless guides the coupling coefficients from waveguide"b"to"a"and from"a"to"b,"described by kaband kbarespectively, are not related by their complex conjugates if the guides are not identical.     

Barrier height engineering on GaAs THz Schottky diodes by means ofhigh-low doping, InGaAs- and InGaP-layers

Barrier height engineering of n-GaAs-based millimeter-wave Schottky diodes using strained InGaAs/GaAs and InGaP/GaAs heterostructures and a high doping surface layer is presented. The Schottky barrier height can be varied between Φ_fb=0.52 eV and Φ_fb=1.0 eV. The use of a pseudomorphic InGaAs layer and/or a thin high doping layer at the surface significantly reduces the Schottky barrier height. This is advantageous for low-drive zero bias mixing applications, A full quantum mechanical numerical calculation is presented to simulate the influence of different high doping layer thicknesses on the diode's dc characteristic. The theoretical results are compared with experimental results, For reverse bias applications (e.g., varactors) a barrier height and breakdown voltage enhancement is realized with a lattice matched InGaP/GaAs heterostructure. The barrier height value is determined by temperature dependent dc-measurements. The epitaxial layered structures are grown by molecular beam epitaxy. The diode devices are fabricated in a fully planar technology using selective oxygen implantation for lateral isolation. The diode's cut-off frequencies are in the THz-range     

The Single Server Queue with Periodic Arrival Process and Deterministic Service Times

We derive an algorithm for computing the exact delay distribution for the following first-come-first-served single server queue. The arrival process is the superposition ofN + 1independent equivalent deterministic arrival streams, and the service times are deterministic. Numerical results are used to compare this system with an approximating system which has been used in the absence of exact results: theM/D/1queue (Poisson input, deterministic service time). A comparison with a finite source model is also given. This study was motivated by the following issue germane to packet switching data networks. There areN + 1packet processes, arriving over identical trunks, which must share the transmission capacity of a single high-speed trunk in a store-and-forward manner. The idealized queueing model above analyzes the worst-delay situation for this problem when the incoming trunks are fully utilized and the packets are maximum sized. The results indicate that anM/D/1approximation can be quite pessimistic in predicting the performance of such a system.     

Voltage transients in electromigration noise measurement data

The 1/f² noise measurement technique used for determination of electromigration lifetime has had only limited practical success. The correlation of noise magnitude to lifetime is high but the results are inconsistent. In this paper the source of the inconsistent results is identified and demonstrated. The presence of voltage transients in noise data, caused by abrupt changes of resistance in a thin-film test structure, is shown to be the primary source of 1/f² noise in the 1–10 Hz frequency range. The transients do not appear consistently in the data and are strongly affected by typical data handling techniques such as windowing. The combination of these factors explains the inconsistent results obtained when using the 1/f² noise measurement technique.     

基于LTCC的微流道散热技术

简要介绍了在低温共烧陶瓷(LTCC)基板中制作微流道结构对电路散热的必要性,建立3种不同结构微流道LTCC基板有限元模型并对其进行了热-流耦合仿真,分别分析不同结构、流体流速及进出口截面对散热性能的影响.基于仿真结果制备实物,实测结果表明14 W/cm2热流密度下最高温升124.3 K,在设定水流流速为0.012 m/...