首先介绍了基于最新Linux内核的防火墙技术netfilter框架结构,包括包过滤防火墙、代理服务器、完全状态检测技术、NAT、DMZ的概念、原理和用途,以及在Linux中具体实现的方法。着重探讨了一个用Perl/CGI编写的集成的WebAdmin来构建一个...首先介绍了基于最新Linux内核的防火墙技术netfilter框架结构,包括包过滤防火墙、代理服务器、完全状态检测技术、NAT、DMZ的概念、原理和用途,以及在Linux中具体实现的方法。着重探讨了一个用Perl/CGI编写的集成的WebAdmin来构建一个集成的带有状态检测功能的防火墙系统,该系统可以通过WebAdmin管理界面来进行本地/远程配置管理整个防火墙的策略,并提供了包括对于ADSL服务获得的动态IP地址的支持,DNS代理的集成,日志的记录,连接追踪,并特别集成了一个PPTPVPN的功能,使得该系统成为一个all in one的防火墙系统。展开更多
Modern electronic circuit requires compact,multifunctional technology in communication systems.However,it is very difficult due to the limitations in passive component miniaturization and the complication of fabricati...Modern electronic circuit requires compact,multifunctional technology in communication systems.However,it is very difficult due to the limitations in passive component miniaturization and the complication of fabrication process.The bandpass filter is one of the most important passive components in millimeter（mm）-wave communication system,attracting significant interest in three-dimension（3D） miniaturized design,which is few reported.In this paper,a bandpass filter structure using low-temperature co-fired ceramic（LTCC） technology,which is fully integrated in a system-in package（SIP） communication module,is presented for miniaturized and high reliable mm-wave application.The bandpass filter with 3D end-coupled microstrip resonators is implemented in order to achieve a high performance bandwidth characteristic.Specifically,all of the resonators are embedded into different ceramic layers to decrease the insertion loss and enhance the out-of-band rejection performance by optimizing the coupling coefficient and the coupling strength.A fence structure,which is formed by metal-filled via array with the gap less than quarter wavelength,is placed around the embedded bandpass filter to avoid electromagnetic（EM） interference problem in multilayer structure.This structural model is validated through actual LTCC process.The bandpass filter is successfully manufactured by modifying the co-fireablity characteristics,adjusting the sintering profile,releasing the interfacial stress,and reducing the shrinkage mismatch with different materials.Measured results show good performance and agree well with the high frequency EM full wave simulation.The influence of layer thickness and dielectric constant on the frequency response in fabricated process is analyzed,where thicker ceramic sheets let the filter response shift to higher frequency.Moreover,measured S-parameters denote the center frequency is also strongly influenced by the variation of ceramic material＇s dielectric constants.By analyzing the relationship b展开更多
文摘首先介绍了基于最新Linux内核的防火墙技术netfilter框架结构,包括包过滤防火墙、代理服务器、完全状态检测技术、NAT、DMZ的概念、原理和用途,以及在Linux中具体实现的方法。着重探讨了一个用Perl/CGI编写的集成的WebAdmin来构建一个集成的带有状态检测功能的防火墙系统,该系统可以通过WebAdmin管理界面来进行本地/远程配置管理整个防火墙的策略,并提供了包括对于ADSL服务获得的动态IP地址的支持,DNS代理的集成,日志的记录,连接追踪,并特别集成了一个PPTPVPN的功能,使得该系统成为一个all in one的防火墙系统。
基金supported by Research Fund for the Doctoral Program of Higher Education of China(Grant No.20060614021)Sichuan Provincial Fundamental Research of China(Grant No.2008JY0057),Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2009J091)
文摘Modern electronic circuit requires compact,multifunctional technology in communication systems.However,it is very difficult due to the limitations in passive component miniaturization and the complication of fabrication process.The bandpass filter is one of the most important passive components in millimeter（mm）-wave communication system,attracting significant interest in three-dimension（3D） miniaturized design,which is few reported.In this paper,a bandpass filter structure using low-temperature co-fired ceramic（LTCC） technology,which is fully integrated in a system-in package（SIP） communication module,is presented for miniaturized and high reliable mm-wave application.The bandpass filter with 3D end-coupled microstrip resonators is implemented in order to achieve a high performance bandwidth characteristic.Specifically,all of the resonators are embedded into different ceramic layers to decrease the insertion loss and enhance the out-of-band rejection performance by optimizing the coupling coefficient and the coupling strength.A fence structure,which is formed by metal-filled via array with the gap less than quarter wavelength,is placed around the embedded bandpass filter to avoid electromagnetic（EM） interference problem in multilayer structure.This structural model is validated through actual LTCC process.The bandpass filter is successfully manufactured by modifying the co-fireablity characteristics,adjusting the sintering profile,releasing the interfacial stress,and reducing the shrinkage mismatch with different materials.Measured results show good performance and agree well with the high frequency EM full wave simulation.The influence of layer thickness and dielectric constant on the frequency response in fabricated process is analyzed,where thicker ceramic sheets let the filter response shift to higher frequency.Moreover,measured S-parameters denote the center frequency is also strongly influenced by the variation of ceramic material＇s dielectric constants.By analyzing the relationship b
