微波热疗天线在生物组织中温度分布的模拟

模拟微波肿瘤热疗条件下生物组织中的温度分布,对临床治疗中微波热疗天线的设计、选择及治疗方案的确定具有重要意义.本文结合电磁场的时域有限差分(FDTD)和温度场的有限差分方法模拟了微波热疗天线在生物组织中产生的温度分布.通过单极子天线对等效组织模型的加热温度模拟结果与实验测量结果比较,对微波热疗天线在生物组织中产生的温度场模拟程序进行了验证.     

用于RFID的平面倒F天线的FDTD设计分析

基于平面倒F天线模型,设计了一种小型的适合用于RFID系统射频标签的微带贴片天线,工作在0.915 GHz频率上.利用基于非均匀网格的时域有限差分方法(Non-uniform Fitine-difference Time-domain,nu-FDTD)对该天线的设计过程进行了建模和仿真,分析了辐射贴片结构的变化对天线的回波损耗的影响,进而对天线进行优化,使得这种平面倒F天线能够适应射频标签天线的需要.     

频率选择表面谐振特性在吸波材料中的应用

利用等效电路法(ECM)及时域有限差分(FDTD)算法分析了频率选择表面(FSS)在2.0～18.0GHz的传输特性,并进行自由空间法测试;同时对含FSS复合吸波材料进行了仿真分析与弓形法反射率测试。结果表明,利用FSS谐振特性与吸波材料吸收特性相互作用,反射率小于–10.0dB的合格带宽可达到7.2GHz(5.0～12.2GHz),有效展宽了反射率曲线的合格带宽,实现了吸波材料吸收性能的宽频化设计。     

三维最优时域有限差分方法

数值色散是时域有限差分方法(FDTD)中最主要的误差来源,导致数值相速成为频率和方向的函数。文中讨论了一种基于最优有限冲激滤波器设计方法的最优差分格式,从频率空间或者波数空间中实现对理想偏微分算子的逼近,构造一种新的具有低数值色散关系的最优时域有限差分方法。文中导出了其数值色散关系和进行了稳定性分析,并通过与常用的基于泰勒级数展开定理的高阶(2,4)时域有限差分法相比较,发现最优时域有限差分法的数值色散得到了极大的改善。最后通过一个数值例子来验证其有效性。     

书讯

正由北京大学王长清、祝西里教授编著的"电磁场计算中的时域有限差分法"一书的第二版已于2014年2月由北京大学出版社作为"中外物理学精品书系"的前沿系列出版。该书全面系统地论述了时域有限差分(FDTD)法的基本原理及其在广泛领域的应用方法,并反映了最新发展成果。前三章介绍了时域有限差分法的基本原理,包括差分格式的建立,数值色散和稳定性以及网格的剖分方法。第四章系统地介绍了应用于开域问题的各种吸收边界条件。第五至七章讨论了时域有限差分法在散射、辐射、微波和光波线路分析中的应用。第八章专门讨论     

基于拉氏变换原理的三维磁化等离子 体电磁散射FDTD分析

 根据拉普拉斯变换(LT)原理,提出了一种新的分析色散介质的电磁特性的时域有限差分(FDTD)算法,称为电流密度拉普拉斯变换时域有限差分(CLT-FDTD)算法.利用磁化等离子体介质中的关于电流密度矢量与电场强度的本构方程,将其两边分别拉普拉斯变换,得到s域内的本构方程.最后进行逆拉普拉斯变换和指数差分,得到在时域里易于求解的FDTD迭代方程.通过该方法计算了非磁与磁化等离子体球的后向雷达散射截面(RCS),验证了该方法正确性与有效性.     

ADI-FDTD方法在乳腺癌检测正向计算中的应用

传统的时域有限差分(Finite-Difference Time-Domain, FDTD)算法受到稳定性条件的制约, 时间步长受限于空间网格的尺寸.医学应用讲究即时性, 为提高成像的速度, 文中采用无条件稳定的交替隐式时域有限差分(Alternating-Direction Implicit Finite-Difference Time-Domain, ADI-FDTD)算法替代传统的FDTD算法进行正向计算, 通过实验得出采用ADI-FDTD算法在保证精度的前提下, 计算时间可缩短为FDTD算法的四分之一, 为乳腺癌微波即时成像提供了可能.     

矩形微带天线的设计及FDTD分析

根据理论计算和实际修正,设计出工作于1.79GHz的矩形微带天线。利用基于非均匀网格的时域有限差分方法对天线进行建模和仿真,并分析了天线的频率特性、远场辐射方向图以及阻抗特性和驻波比。     

并联介质加载折叠臂偶极天线的辐射特性

介绍了一种由折叠臂偶极天线和并联介质块组成的小型化超宽带天线。分析了天线的辐射机理,应用时域有限差分(FDTD)方法和完全匹配层(PML)技术对天线的辐射特性进行了研究。计算结果表明:驻波系数小于3时,天线的阻抗带宽达到2.4GHz(3~5.4GHz),并且辐射脉冲保形性较好,可用于无载波超宽带无线数据通信系统。     

开口式微波加热器的研究

应用时域有限差分法(FDTD)分析和计算了一种开口式同轴加热装置。同时讨论和计算了为防止微波泄漏而设计在腔体外围的扼流槽的作用。测量结果与计算结果有相当高的一致性。表明这种装置可以在中心处产生高温,而在设计相关的微波装置时,使用时域有限差分法又是十分有效的。     

A New MIC Magic-T Using Coupled Slot Lines

Novel microwave integrated circuit (MIC) 180/spl deg/ hybrids (magic-T's) suitable for MIC are described. They make use of the two orthogonal modes (even and odd) of the coupled slot lines, and, therefore, have special port location, which is quite different from that of the conventional 180/spl deg/ hybrids such as a rat-race. That is, the two-ports, which correspond to the E-arm and the H-arm of the well-known waveguide magic-T, can be located on the same side, opposite to the other two ports. This feature is of a great practical advantage when applied to an MIC, because the crossing of the transmission lines can be omitted when this type of magic-T is applied to balanced-type circuits such as balanced mixers. Satisfactory experimental results at a center frecuency of 6 GHz are given. The isolation between the E- and the H-ports is better than 30 dB over an octave band, and the frequency sensitivity of the coupling is almost flat in the frequency range from 2 to 10 GHz.     

K-Band Integrated Double-Balanced Mixer

A novel microwave integrated circuit (MIC) double-balanced mixer with good isolation between the three ports is described. The mixer is fabricated using a combination of microstrip lines, slotlines, and coupled slotlines, together with four beam-lead Schottky-barrier diodes. The K-band magic-T has been developed for the double-balanced mixer. The minimum conversion loss measured at a signal frecuency of 19.6 GHz is 4.7 dB. Isolation between RF and LO ports is greater than 20 dB from 18 to 21 GHz. The mixer can be expected to have wide applications in MIC receivers and transmitters up to the millimeter-wave band.     

C波段高增益圆极化微带天线阵的研制

论述了圆极化微带天线阵的设计方法。以工作频率为5.8GHz,32单元圆极化微带天线阵为研究对象,设计出了与馈电网络为一体、具有圆极化特性的微带天线阵,从而解决了圆极化微带天线阵馈电网络较为复杂、工程实现较为困难这一问题。实验结果表明该天线阵具有良好的圆极化特性,进而说明了该方法是有效可行的。     

An Equivalent Circuit Model for Broadband Modified Rectangular Microstrip-Fed Monopole Antenna

A new, simple equivalent circuit model for designing a multi-mode/broadband modified rectangular microstrip-fed monopole antennas using stepped cut at four corners (SCFC) method has been presented in this paper. The SCFC method is a method in which the four corners at the edges of the patch are cut for the purpose of designing the microstrip-fed monopole antenna. The design procedure of a single mode to a broadband microstrip-fed monopole antenna is explained in order to help understand more about the proposed equivalent circuit model and SCFC method. The computer simulation technology (CST) microwave studio and advanced design system (ADS) software are used to design and simulate of the proposed microstrip-fed monopole antennas and their equivalent circuit model, respectively. The operating bandwidth of the broadband antenna with \(\hbox {S}_{11}< -10\) dB, covers the operating frequency range from 0.9 to 2.6 GHZ that it is suitable for GSM (0.9 GHz), WiFi (2.4 GHz) and LTE (2.6 GHz) applications. For the purpose of validating the simulated results, the antennas prototype has been fabricated and measured. The comparison of the measurement and simulation results shows that, there is a good agreement between them.     

Novel configurations of planar multilayer magic-T usingmicrostrip-slotline transitions

Novel configurations of microwave planar magic-T suitable for microwave integrated circuits (MICs) and monolithic MICs are described. They consist of microstrip and slotline T-junctions coupled by microstrip-slotline transitions. Since via-hole processing is not encountered, they are especially applicable to multilayer MICs. Derived equivalent network models are used efficiently for the design of the corresponding multilayer microstrip magic-T. Measured data and numerical simulations showing good amplitude and phase characteristics over an octave operating bandwidth validate the proposed configurations of planar magic-T     

Design of GaAs MESFET Oscillator Using Large-Signal S-Parameters

A design method of GaAs MESFET oscillator using large-signal S-parameters has been discussed. Together with the measurement results of the dependence of Iarge-signall S-parameters on power levels and bias conditions, computer analysis of the equivalent circuit for MESFET'S has qualitatively clarified the large signal properties of MESFET'S. On the basis of these findings, S-parameters have been designed for the MESFET oscillator over the frequency range of 6-10 GHz, which has resulted in power output of 45 mW at 10 GHz with 19-percent efficiency, and 350 mW at 6.5 GHz with 26-percent efficiency, respectively. Good agreements between predicted and obtained performances of MIC positive feedback oscillator have been ascertained, verifying the validity of the design method using large-signal S-parameters.     

A Planar Magic-T Using Substrate Integrated Circuits Concept

In this letter, a slotline to substrate integrated waveguide transition is proposed for the development of substrate integrated circuits. The insertion loss of the back-to-back transition is less than 1 dB from 8.7 to 9.0 GHz. With this transition, a planar magic-T is studied and designed. Measured results indicate a very good performance of the fabricated magic-T is observed within the experimental frequency range of 8.4-9.4 GHz. The amplitude and phase imbalances are less than 0.2 dB and 1.5deg, respectively.     

一种平面魔T结构的研究

为在小体积范围内产生雷达和信号、差信号,介绍了一种宽带平面型魔T结构的实现方法。通过选取合适的电路结构,并借助微波EM分析软件,在微带线和槽线的基板上实现了平面型魔T结构电路功能,在较宽的频带内实现了良好的幅相特性,并给出了测试结果。同时表明作为一种传输线结构二槽线,有其独特的优点和应用价值。     

A unified approach for the steady-state analysis of resonantconverters

A generalized approach for the steady-state analysis of resonant converters is presented. Different resonant converter tank circuit configurations are combined into a single tank circuit referred to as a generalized tank circuit. The load presented to this tank circuit is represented by an AC equivalent resistance, and simple complex circuit analysis is used to analyze such a generalized tank circuit. This type of unified approach simplifies the method of analysis for different configurations and eliminates the need for analysis of different schemes separately. In addition, in a computer program, the results for a particular scheme can be obtained by opening or shorting the nonrequired tank circuit components of the generalized scheme. The effect of high-frequency transformers and other parasitics can be taken into account in the analysis. A design example is presented to illustrate the method of designing a converter, and experimental results are presented to verify the analysis     

差分LC VCO的设计方法

通过分析振荡器的两种典型相位噪声模型,给出了振荡器相位噪声与电路参数的关系。在此基础上,提出了优化VCO相位噪声的设计方法：设计高Q值电感;调整尾电流的大小;调整nMOS管和pMOS管的尺寸。文章最后给出了一个2．4GHz全集成VCO的设计,仿真结果表明在2．4GHz时VCO的相位噪声为-120．4dBc／Hz@600kHz,证明该方法对于VCO的设计具有较好的指导作用。