Lumped element modelling of coplanar series RF MEMS switches

A lumped element model for microwave MEMS switches in series configuration is discussed. The equivalent circuit that is presented, composed of inductors, resistors and capacitors in the OFF state, can be easily implemented in commercial software packages. Good agreement with experimental results confirms the validity of the proposed model.     

Design procedure for inhomogeneous coupled line sections

Design formulas are presented, along with a procedure for the design of inhomogeneous coupled line sections as an approximation to a series open-circuited stub for application in the realization of microwave pseudo-high-pass filters. The accuracy of the design equations is evaluated through the design and test of a seventh-order filter and it is found that the formulation predicts the performance of the section well beyond the quarter-wave frequency     

为企业网络部署第二道安全防线

企业部署了防火墙后,是否还需要进一步提升安全级别?答案是肯定的。不错,防火墙的确称得上是安全防护的第一卫士。同时,部署防火墙也是对直接接入互联网开展业务的企业的一项基本要求,但是仅有一道防线的城池并非固若金汤。我们知道,防火墙是通过执行由网管员创建的预定义策略来决定允许或拒绝流量的。策略是由各种准则,包括每个通信的来源、目的地和协议的“接受”和“拒绝”等规则共同组成的。多数防火墙都支持一定数量的应用协议,如SMTP、FTP、HTTP和DNS,以便将不安全流量拒之门外的同时,保证企业在互联网上正常开展业务。但对攻击…     

Neural networks for frequency line tracking

This paper investigates the application of neural networks to frequency line tracking. Recently, hidden Markov models (HMM's) have been successfully applied to this problem, and here, we study a neural network architecture called Mnet, which is based on an underlying Markov model representation. A supervised learning algorithm is developed for Mnet, and a method of analytically deriving the connection weights for the Mnet is also mentioned. Two more conventional neural networks are also studied; a multilayer feedforward network and a multilayer network with feedback. The simulation results show that all three neural networks are comparable in performance to a hidden Markov model when applied to the frequency line tracking problem     

Boundary element analysis of a trapezoidal transmission line

A full-wave analysis is a transmission line with a trapezoidal cross-section is described. The boundary element method (BEM) is used, and by making a convenient choice for the dyadic Green's function, it is shown to be very efficient in comparison to alternative methods of analysis. It is shown that for electrically small dimensions, spurious solutions are suppressed by the selection of integral equations. The analysis is verified by comparisons to calculated results from a vector finite element computer program, and some dispersion data are presented     

Pattern synthesis with a feed network consisting of lossytransmission line sections

A method for feeding the elements of an antenna array with a lossy transmission line section is presented. Four examples showing the applicability of the method are given. The behavior of the system in a frequency band around the design frequency is studied. Besides changes of physical length, changes in the frequency bandwidth of the antennas are observed     

求解线性集总参数电路的变分方法

变分原理在电磁场有限元计算中已获广泛应用,本文讨论如何将该原理应用于线性集总参数电路的求解中。笔者从特勒根定理出发,导出了基于节点电压和圊路电流的功率泛函,给出了通过变分获得电路解答的方法和步骤,借助功率泛函的概念,指出了电路解答与电路系统的功率最小点或者功率驻定点相对应。数值算例验证了这一结论。本文目的是提供一个清晰的视角理解线性集总参数电路求解的物理本质。同时,集总参数电路的泛函是求解电磁场一电路耦合问题的桥梁之一。     

Location of structural sections from within a highly distorted complex line drawing

Complex and highly distorted line drawings are produced by subjects attempting the Rey Complex Figure test, a clinical test of neuropsychological assessment. However, the marking scheme conventionally employed can be subjective and unreliable. In this paper, the first stages in automating this scoring system are investigated using a robust technique to locate a reduced set of scoring sections and a knowledge-based system that employs spatial metrics and fuzzy approximation techniques. Testing the technique using clinical data produced encouraging results that support the argument that this is a feasible approach for implementing a fully automated system, and that in its current state, can be immediately applied in a semi-automated system.     

Lumped Parameters of a Reentering Cylindrical Cavity

The cylindrical reentering cavity is studied. It is shown how lumped equivalent parameters can be known that are one inductance and two capacitances. These elements can be measured experimentally. Thus the problem of coupling with an active solid-state element, defined itself by lumped equivalent parameters (inductances and capacitances), is accurately solved.     

An enhanced transmission line model for conductors with arbitrary cross sections

An enhanced transmission line model (ETL) has been recently proposed to describe the propagation along two parallel wires with circular cross sections up to wavelengths comparable to the distance between the wires. In this paper, a general ETL model is proposed to describe the propagation along interconnects consisting of wires with arbitrary cross sections. Since the ETL model has the same simplicity of the standard transmission line model, it allows investigating high-frequency effects, like radiation and dispersion, with a computational cost which is sensibly lower than that required by a full-wave numerical simulation. The ETL model is obtained, with suitable approximations, starting from a full-wave analysis of the propagation problem and using an integral formulation based on the electromagnetic potentials satisfying the Lorentz gauge. Some case studies are carried out and discussed, including a benchmark test with existing literature, performed to check the validity and accuracy of the proposed model.     

Wide-band resistorless all-pass sections with single element tuning

This paper presents three first order resistorless all-pass filters using combinations of current controlled current conveyors (CCCII) and a unity gain buffer. All circuits feature single element tuning, low sensitivities, and low output impedances, therefore they are suitable for cascading. Circuit simulation results are found in good agreement with theoretical analysis.     

The experimental determination of equivalent networks for a coaxial line to helix junction

Equivalent networks were determined for a right angle transition between a coaxial line and a shielded helix. By employing a movable mercury short on the helix it was possible to determine these equivalent circuits through the use of well-known microwave measurement techniques. Utilizing the possible physical connection which might exist between the junction and its equivalent circuit, an attempt was made to measure quantitatively the effect of varying various parameters in the junction. For the limited number of cases studied, no simple connection between the elements of the equivalent circuit and the physical parameters of the junction was discovered. Although the results for the equivalent networks were very sensitive to small experimental errors, by using these networks it was possible to calculate reasonably accurate values of input impedence in the coaxial line for known impedance terminations on the helix.     

Paired block line codes for pure photonic networks

New line coding schemes called paired block codes (PBC) are investigated for application in future pure photonic networks. The first block of each pair utilises coding rule violations to simplify transmission frame structures to facilitate frame processing to complement limited capabilities of photonic logic devices. The second block is provided with sufficient redundancies to attain photonic clock recovery through logical processing. An upper bound efficiency of this type code is 75%.<>     

A lower bound for the length of nonuniform transmission line matching sections

A lower bound for the length of a nonuniform transmission line section needed to match a given load impedance to a given real input impedance is derived. The bound depends not only on the load and input impedances, but also on the maximum and minimum permissible values of characteristic impedance within the nonuniform line. Several specific cases are presented to illustrate the tightness of the bounds.     

Merits of low-density WDM line systems for long-haul networks

Conventional wisdom claims that the higher the number of wavelengths supported by a dense wavelength-division multiplexing transmission system's line system the better, since the high costs of amplifiers are split among more revenue-generating entities. For example, a 20/spl lambda/ link must cost less than 25% of the cost of an 80/spl lambda/ link to compete at full (80/spl lambda/) fill, assuming four 20/spl lambda/ links need to be deployed in parallel. We show that this is not necessarily the case if network considerations and technology evolution are taken into account. In particular, we show that a 20/spl lambda/ link can cost as high as 64-79% of the cost of an 80/spl lambda/ link and still be competitive at full fill, while providing much lower initial cost. This is because of the cost reduction of technology over time, economic considerations (net present value), nonuniform capacity needs in real networks, and how network maintenance can be achieved. We also reason why such lower end systems can indeed achieve the required cost reduction.     

集总参数微型滤波器在雷达中的应用

介绍一种集总参数LC微型滤波器的性能和特点,以及在雷达接收通道、频率源中的应用,还提供了几组有代表性的滤波器频响特性。     

An adaptive canceller of cochannel interference for spread-spectrummultiple-access communication networks in a power line

The authors propose and investigate an adaptive canceller of intersymbol and cochannel interference due to channel distortion and cross-correlation among pseudonoise sequences assigned to individual users of a DS-SSMA (direct-sequence spread-spectrum multiple-access) system. In order to implement a local area network (LAN) by using a power line installed in a building wall as a transmission channel, the authors have investigated utilization of DS-SSMA which has advantages such as robustness against narrow-band interference and noise and realization of asynchronous code division multiple access. In a power line, however, restriction of transmission bandwidth for communications makes it difficult to suppress cochannel interference and the channel is also time-varying due to fluctuation of loads. Since the proposed canceller adaptively eliminates cochannel interference as well as intersymbol interference, it can facilitate synchronization and increase the number of the simultaneously accessing users on a power line with restricted processing gain. The error probability in the output of the canceller is theoretically calculated for the steady-state case by using a Markov model. Computer simulations illustrate stable convergence properties of the canceller     

Operations standards for global ATM networks: network element view

The International Telecommunication Union (ITU) has completed work on a series of standards on asynchronous transfer mode (ATM) equipment functional operations and network element management. The objective of these standards is to enable flexible design and interoperability of network elements for use in a global ATM network, independent of any specific implementation. This article discusses these standards with respect to their development and application in planning ATM networks. Specifically, it addresses the following: the modeling approach taken in the development of the ITU standards, key operational features specified in the ATM network element functional model, and the capabilities of the ATM network element management interface. Examples of ATM equipment are provided to illustrate how the functional models specified in the ITU standards may be used by network planners and equipment manufacturers to specify and develop ATM equipment tailored to specific needs, while ensuring network interoperability. The article concludes with some points on the future enhancement of these and related ATM equipment operations standards     

Thin bandpass filters containing sections of symmetric strip transmission line

Thin (1-mm thick or thinner) combline bandpass filters based on sections of symmetric strip transmission lines and containing closely spaced (0.1–0.2 mm apart) stepped-impedance resonators are described. It has been found that, if these filters are made on high-permittivity ceramic substrates, their dimensions prove to be smaller than the dimensions of other ceramic-based filters. Various frequency characteristics of these filters—symmetric, with increased one-sided selectivity, and with a constant delay time—have been analyzed. The experimental results obtained for a 1-mm-thick bandpass filter with ? _r = 9.7 are in good agreement with the computer-simulation data.