Narrow-band stripline filters with transmission zeros at finite frequencies

A design method is described to realize narrow-band stripline or microstrip bandpass filters having one transmission zero near to the upper and lower bandedge. The filters utilize capacitively coupled open half-wave TEM-line resonators. Two nonadjacent resonators are also inductively coupled. No short circuits are needed. The design is based on the approximate or exact synthesis of the lowpass protoype presented by Levy. The transmission line parameters are obtained easily from the design formulae which have been derived using the susceptance (or reactance) slope parameter technique. The filter performance is good up to 12 per cent bandwidth. Measured results show good agreement with the theoretical ones.     

一种带状线馈电的新型宽带印刷偶极子天线

本文在分析传统微带巴伦馈电印刷偶极子天线的基础上,对天线馈电形式及辐射振子结构进行了改进设计,通过将馈电网络设计为带状线形式,并采用两面对称的辐射振子结构,提出了一种带状线馈电的新型宽带印刷偶极子天线,这类天线具有较宽的阻抗带宽(驻波小于2的带宽可做到45%以上)。这种新型带状线馈电印刷偶极子天线的馈电网络适于与天线阵的馈电网络进行一体化设计,适合于用印刷电路技术大批量生产,是大型天线阵的一种理想的辐射单元形式。     

Simple examples of the method of moments in electromagnetics

Three simple examples of the use of the method of moments in electromagnetics, i.e. analysis of the input impedance of a short dipole, and plane-wave scattering from both a short dipole and two coupled short dipoles, are presented. The relative simplicity of the examples is a direct result of obtaining simple expressions for the elements in the method-of-moments impedance matrix     

Time-domain magnetic field waveform measurement near printed circuit boards

This paper describes a time domain magnetic field measurement process for measuring magnetic fields near printed circuit boards (PCBs) with a loop probe. In carrying out these measurements, the loop probe needs to be calibrated in the frequency domain. In this process, a microstrip line with a teflon substrate serving as the standard magnetic field source is employed as a means of calibrating the probe. The standard magnetic field intensities of the line are calculated by using an approximate equation obtained from Ampère's law to simplify the calibration. The sensor-factor of the probe obtained from this method agrees with that obtained through the use of a standard G-TEM cell in 2 dB at frequencies below 1 GHz. The waveforms of magnetic fields near a PCB having a four-layer construction are measured using a 10 mm diameter loop probe as the calibrated magnetic field sensor. The generation of magnetic field waveforms causing the radiated emission from the PCB is found to depend on the circuit operating conditions. Our results clarify the fact that the time domain magnetic field measurement process is an effective tool for analyzing the sources of emission radiated from PCBs and for investigating the radiation mechanism. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 9–18, 1998     

Compact third-order microstrip bandpass filter designed by the distributed- to lumped-element equivalence

In reality, it is not easy to design microstrip filters for the sake of distributed-element effect. It is an effective approach to approximate distributed-element structures through appropriate lumped-element circuits. In this paper, some basic microstrip structures are discussed, whose equivalent lumped-element circuits are derived. Then, a novel microstrip filter is obtained by connecting these microstrip structures, according to the similar topology of the third-order lumped-element bandpass filter. The equivalent lumped-element counterpart of the proposed microstrip filter clearly reveals its physical mechanism, ie, how the resonances are created and coupled and how the transmission zeros are created. Furthermore, a set of the design formulas are presented, which can be used to calculate initial structure parameters and then facilitate design process. The proposed microstrip bandpass filter can realize a third-order elliptic bandpass response with one transmission zero at each side of the passband. In addition, two short-circuited stubs are added to input/output ports to create the third transmission zero. The filter is featured by good frequency selectivity and out-of-band suppression. For demonstration, an actual example was designed, fabricated, and measured.     

Modelling of printed discontinuities on open microstrip lines by mode matching techniques

The dynamic analysis of discontinuities in printed circuits has been performed using the mode matching technique. This study concerns the open end of microstrip lines and suspended microstrip lines. The fields on either side of the discontinuity are described by means of the continuous (radiated and evanescent) and guided modes of the structure. The conditions of continuity of the electromagnetic fields are then applied in the plane of the discontinuity. By taking into account the relations of orthogonality of the modes of the same region, a system of coupled Fredholm integral equations is obtained and solved by the iterative method of Neumann's series. The study calls for the use of the continuous spectrum of microstrip lines, which can be obtained analytically only after a great amount of calculation and CPU time. Thus, the first approach consists in neglecting this continuous spectrum. This gives accurate results for the reflection coefficient but it is not sufficient for the derivation of the radiation pattern. So, two simple models for the continuous spectrum, both based on the physical behaviour of such discontinuities, are considered and discussed. © 1997 John Wiley & Sons, Ltd.     

A practical approach to EMC education at the undergraduate level

In view of the importance of electromagnetic compatibility (EMC), universities worldwide are paying more attention to training electronic engineers with good EMC design knowledge. As part of the EMC training, a practical printed circuit board (PCB) layout project has been offered as an elective to the undergraduates in the authors' universities. The project requires the students to design the PCB layout of a standard digital circuit twice, the first time with no EMC consideration at all, and the second time with careful EMC consideration. The significant difference in the levels of radiated emissions of the two layouts allows the students to appreciate the importance of EMC design at an early stage of product development.     

Effect of dipolar arrays on the localization of charge carriers inmolecular materials

The paper presents results of calculations of the depth and distribution of local states for charge carriers created by polar impurities in a model molecular material. Equations resulting from the electrostatic model due to Lyons have been employed in the calculations. The presence of polar species in a non-polar molecular material locally modifies the polarization energy, thus creating local states (traps) on neighboring molecules. Calculations performed for an isolated dipolar defect show that traps as deep as ~0.4 eV to ~0.5 eV can result in such a way, their depths and cross-sections depending on the dipole moment of the guest molecule. Results of similar calculations carried out for arrays of spatially connected dipoles indicate that local states of a considerable density may be created, modifying the density-of-states function, and hence influencing the effective mobility of charge carriers     

Simulation-based evaluation of SAR and flip angle homogeneity for five transmit head arrays at 14 T

Introduction

Various research sites are pursuing 14 T MRI systems. However, both local SAR and RF transmit field inhomogeneity will increase. The aim of this simulation study is to investigate the trade-offs between peak local SAR and flip angle uniformity for five transmit coil array designs at 14 T in comparison to 7 T.

Methods

Investigated coil array designs are: 8 dipole antennas (8D), 16 dipole antennas (16D), 8 loop coils (8D), 16 loop coils (16L), 8 dipoles/8 loop coils (8D8L) and for reference 8 dipoles at 7 T. Both RF shimming and k_T-points were investigated by plotting L-curves of peak SAR levels vs flip angle homogeneity.

Results

For RF shimming, the 16L array performs best. For k_T-points, superior flip angle homogeneity is achieved at the expense of more power deposition, and the dipole arrays outperform the loop coil arrays.

Discussion and conclusion

For most arrays and regular imaging, the constraint on head SAR is reached before constraints on peak local SAR are violated. Furthermore, the different drive vectors in k_T-points alleviate strong peaks in local SAR. Flip angle inhomogeneity can be alleviated by k_T-points at the expense of larger power deposition. For k_T-points, the dipole arrays seem to outperform loop coil arrays.

     

HORIZONTAL WIRE ANTENNA ABOVE LOSSY HALF-SPACE: SIMPLE ACCURATE IMAGE SOLUTION

A simple, approximate, but highly accurate, method is proposed for the analysis of horizontal thin-wire antennas above a lossy half-space. In the first step, the contribution of the lossy half-space to the field of a horizontal Hertzian dipole above the interface, both in the half-space above and in that below the interface, is approximated by the field of few (typically six) equivalent sources (images). The relative image intensities are obtained by enforcing the boundary conditions for the tangential components of the electric and magnetic field at a number of points at the interface. The field of the images is introduced into the Hallén equation; current distribution is approximated by polynomials and determined by point-matching. The results for the impedance of horizontal dipoles obtained by the present method are in excellent agreement with the exact results (obtained from the Sommerfeld theory), although the proposed method is conceptually much simpler and requires at least an order of magnitude less computing time than the exact method.     

Numerical analysis of offset-line-source-fed microstrip reflectarrays

A high-gain offset-fed microstrip reflectarray fed by single and double line sources (where the line sources are ground-plane-backed colinear dipole arrays) is analyzed numerically. This offset-fed configuration with its patch array implemented using rectangular patches only, and again using a combination of different patch geometries, is rigorously investigated. Some parameters of the reflectarray, such as phase errors, radiation patterns, directivities, spillover efficiencies and bandwidth, are analyzed, and its bandwidth is compared to that of a centre-fed configuration.     

A compact quadruple crossed-dipole microstrip antenna designed for dual frequency and beam scanning operation

A synthesis of a compact crossed-dipole microstrip antenna is introduced. An attempt is made to include most of the operating characteristics required in modern communication systems. The antenna is composed of four crossed dipoles, forming a 2×2 element planar array that radiates an elliptically polarized field, operates in the ranges from 1.8 GHz to 1.9 GHz (DCS) and from 2.5 GHz to 2.8 GHz (UMTS) and has a satisfactory power gain. The feeding of interconnected dipoles is obtained using folded microstrip lines that minimize the size of the structure and also the parasitic radiation. The overall array has eight probe-fed ports. Their suitable phase excitation can drive the antenna to produce patterns with a maximum value in the desired directions.     

一种新型对称宽边耦合共面波导巴仑的分析

本文介绍了一种新型对称宽边耦合共面波导巴仑。它是基于一般耦合传输的网络模型结合对称宽边耦合共面波导理论导出的。作为一个例子，我们设计了中心频率12GHz巴仑，其输出辐相特性优于文献[1]对称宽边耦合微带巴仑。所研究的巴仑可地微波单片集成电路（MMIC）和多层介质微波集成电路（MuMIC）的混频器、调制器和倍频器等诸多微波器件中。     

Development of an integrated CAD tool for switching power supplydesign with EMC performance evaluation

A computer-aided tool for the design of switching power supplies integrating a layout editor, autorouter, component library builder and EMI simulator is presented. The software takes on a modular approach and develops the printed circuit board (PCB) layout with emphasis on electromagnetic compatibility (EMC). The prediction of interference level is achieved by SPICE simulation with suitable model assignments of EMI sources, components, and PCB tracks. An offline forward power converter is built and measured to verify the simulated result. Finally, a performance index is introduced to act as an indicator for the EMC performance of a given PCB layout     

A novel method for wave focusing investigation in metamaterial half‐space and slab lens structures

Approximate image currents for the Sommerfeld half‐space problem with vertical electric and magnetic current sources above double negative half‐space is found using the discrete image theory and Laplace transform. This method would found its applications in investigation of dipole radiation above metamaterial half‐space and in describing the focusing mechanism of metamaterial lenses. In order to efficiently consider the effects of metamaterial half‐space, discrete image dipoles are defined by proposing an exponential series for reflection coefficient. Unknown constants (the loci of images) in the argument of the exponential function are determined by equating the coefficients of the Taylor series for exact reflection coefficient with those of the proposed approximate series. Thus, the calculation of integral with oscillating integrand reduces to the solution of polynomial equation for the zeros of polynomials. As an application for the proposed approach, the field focusing in double negative is investigated. Thanks to the fast and accurate methods for finding the zeros of polynomials, it is shown that in addition to its good accuracy, this method decreases the computational time for field calculations in comparison with the exact methods. It is seen that for the negative refractive index beside −1, the complex images approach to infinity and have negligible effect on the scattering field of dipole. For the other negative indexes the complex image blurs the real image. Copyright © 2015 John Wiley & Sons, Ltd.     

Transient analysis of printed lines using finite‐difference time‐domain method

Comprehensive studies of ultra‐wideband pulses and electromagnetic coupling on printed coupled lines have been performed using full‐wave 3D finite‐difference time‐domain analysis. Effects of unequal phase velocities of coupled modes, coupling between line traces, and the frequency dispersion on the waveform fidelity and crosstalk have been investigated in detail. To discriminate the contributions of different mechanisms into pulse evolution, single and coupled microstrip lines without (ϵ_r = 1) and with (ϵ_r > 1) dielectric substrates have been examined. To consistently compare the performance of the coupled lines with substrates of different permittivities and transients of different characteristic times, a generic metric similar to the electrical wavelength has been introduced. The features of pulse propagation on coupled lines with layered and pedestal substrates and on the irregular traces have been explored. Physical interpretations of the simulation results are discussed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Reduction of electromagnetic field coupling to microwave microstrip circuits

The signals induced by an external electromagnetic field along a microstrip line on a multilayered dielectric substrate were studied. The main target of the work is not to introduce a new technique of study but to search for suitable combinations of the structural and geometrical characteristics of the printed geometry whereby the electromagnetic interference of the external field to the circuit would be reduced. This reduction is desirable in all modern applications. The results derived prove that this object can be achieved at high frequencies and when the substrate is multilayered.     

通过串音预测实现PCB的电磁兼容性设计

对PCB串音进行分析 ,归纳出影响串音的因素 ,以便在PCB设计中能够采取针对性措施 ,从而有效地降低串音和EMI水平。主要从PCB地线面结构布局方面考虑串音问题 ,通过分析不同地线面结构对串音大小的影响 ,得出部分满足电磁兼容性的PCB设计原则。     

A study of dielectric relaxation in aluminosilicate-filledlow-density polyethylene

Space charge formation in low-density polyethylene (LDPE) filled with zeolites and clays has been investigated by the thermally stimulated current method. The presence of fillers affects the dielectric properties due to additional dielectric relaxation phenomena, which depend on the structure of the inorganic filler. Pores or cages existing in the zeolite frame enable their compensated ions to move away from their neutral position under electric field to form dipoles of very low activation energy and high attempt-to-escape frequency. The activation energy is related to the pore sizes of zeolites. However, kaolin-based clay which has movable cations on its surfaces form an interfacial dipole between the LDPE and clay. A `Maxwell-Wagner' interfacial relaxation behavior was observed in the clay-filled LDPE system. The activation energy of interfacial relaxation of the clay-filled LDPE system is higher than that of dipole relaxation of the zeolite-filled LDPE     

Preparing and polarizing stability of Teflon AF nonlinear opticalpolymer electret double layer film system

Nonlinear optical activity of an nonlinear optical (NLO) polymer electret originates from the preferential orientation of dipoles doped or chemically attached to the polymer matrix. In this paper, the idea of fabricating a Teflon AF/nonlinear optical polymer electret double layer film system is proposed to improve the orientation stability of the dipole in the polymer electret. The polar stability has been investigated by means of measuring the open-circuit thermally stimulated depolarization (TSD) spectrum, the electro-optical coefficient, and the isothermal surface potential decay. The results indicate that the double layer film system may markedly increase the orientation stability of the dipole in the NLO polymer layer. Because the Teflon AF layer has high charge storage stability, the dipole orientation can be bound by the electric field generated by the space charge in Teflon AF layer