宽带接入的现状和未来趋势

宽带数字通信的持续发展不断地对现有公用网络的能力提出的新的要求。在支持电信业务的新的接入技术大量涌现的同时，管制制度的重大变革也在对电信市场进行着重塑。本文描述了宽带业务的现状和接入结构与技术的发展趋势。     

IP城域传输网的特点和解决方案

介绍了城域传输网的业务要求、规划原则以及宽带多业务传输网的几种实现方案,最后提出了吉林省城域传输网的解决思路。     

乘子法及C波段宽带GaAs FET放大器

本文探讨一种新乘子迭代的乘子法.并用于计算机优化设计有约束条件下的GaAsFET放大器.乘子法中,为使乘子λ~(?)收敛到有限值,文章建议应选择参数C初始值.使之与被优化目标函数权因子的最大值在同一数量级.作者将研制成功的二个三级GaAs FET放大器进行级联后测试.在3～7.4GHz频率范围内.得增益49=2.5dB,最大噪声系数3.6dB(典型3.3dB),1dB增益压缩点的最小输出功率-13dBm.实验证实乘子法是行之有效的.文中给出基于匹配网络综合理论分析得到的三级GaAs FET放大器新的拓扑类型及网络元件的计算机优化值.     

天线宽带匹配网络的粒子群优化设计

提出了基于粒子群优化算法(Particle Swarm Optimization,PSO)设计天线宽带匹配网络的方法;采用了等效阻抗方法解决了UHF频段天线宽带匹配网络实际制作中元件值随频率畸变较大的困难;最后利用上述方法设计了一付30~512MHz全向超宽频带小型化天线的匹配网络,设计结果使得带内VSWR<3.0,并与实验结果吻合良好。     

圆锥印刷四臂螺旋天线的分析与设计

提出了一种应用于全球定位系统(GPS)的宽波束圆极化圆锥印刷四臂螺旋天线。数值分析表明螺旋角和螺旋臂的长度是影响波瓣宽度的两个主要因素,文中给出了其变化规律。基于此,我们设计了一个中心频率为1.57542GHz的圆极化圆锥印刷四臂螺旋天线,并制作了模型天线。测试结果显示该天线在中心频率处的3dB波瓣宽度约为200°,满足半球覆盖特性;3dB轴比带宽约为0.35GHz;驻波比在1.5以下的频率范围为1.47~1.6GHz。实验结果和仿真结果吻合良好。     

Penetration of broadband services – The role of policies

Penetration of broadband services is seen as a key for developing Europe into an information society. This paper provides an overview of broadband policies in the EU, South Korea, Japan and US. On this background, the paper discusses how active policy can stimulate the demand for broadband services.     

A technique for elimination of reflected rays from antenna measurements performed in echoic environment

The paper describes a technique for analyzing antenna measurements and removing reflected components present in measurements performed in echoic environments. The method is based on digital signal processing methods, and frequency-domain measurements are used to design a discrete-time, finite impulse response digital filter using least-squares methods. The frequency response of the filter is equal to the transmission coefficient measurements performed in an anechoic chamber. In order to verify the method, processed measurements of mutual coupling between stacked patch antennas were compared to the computer simulations of anechoic response, and a very close agreement was achieved.     

宽带接入市场初探

简述当前宽带接入网建设和市场竞争情况,提出了发展用户宽带接入网应考虑的重点问题,并指出宽带网发展的决定因素,避免资源浪费、商家间的协调等5个需要注意的问题。     

高气压CO2激光器宽带输出频谱特性的理论研究

从理论上研究了高气压CO2激光器的宽带输出频谱特性.结果表明,在20个大气压下,CO2激光器有宽带输出,带宽高达5.0 cm-1(相当于150 GHz),从971 cm-1~976 cm-1,峰值在10R(16)线处,10R(14)线和10R(18)线差不多对称地分布其两侧.很小的增益差异(4.6%)造成了很大的能量输出差异(100多倍).比较了谐振腔内有无色散元件时的输出频谱,理论证明了谐振腔内无任何色散元件时的宽带输出频谱是光滑连续的,而频率依赖的反馈引起了输出频谱很强的精细结构.理论计算结果与实验测量结果符合较好.     

Two-dimensional J-spectra with absorption-mode lineshapes

Two-dimensional J-spectroscopy offers the possibility of a complete separation of chemical shifts and J-couplings. However, the usefulness of the experiment is considerably reduced by the fact that peaks in the spectra have the phase-twist lineshape. We present a simple new spectroscopic method for recording J-spectra in which the peaks are both in the absorption mode and retain their natural intensities, albeit at the cost of a considerable reduction in the signal-to-noise ratio. No special data-processing is required. The method is tested on quinine, and the steroid dehydroisoandrosterone.