A spherical representation of the Smith chart

In this article a limitation of the conventional 2D Smith chart has been highlighted and discussed. An extension to the Smith chart has been proposed in an attempt to overcome these limitations. The extension involved transforming the 2D impedance plane into three dimensions and mapping it onto the surface of a sphere. This is believed to be the first time that this formulation of the Smith chart has been presented. A number of representations of the spherical Smith chart were then considered. These included the use of constant resistance, reactance, impedance, and reflection coefficient lines. Finally some of the issues associated with the graphical displaying of the 3D Smith chart were discussed.     

利用2.4GHz WLAN前端模块实现多无线技术共存

引言 @@ 无线局域网(WLAN)技术现已成为了家用和工业用电器中移动计算及数据通信的必然标准.近来,这种技术更被用于无线互联网语音(VoIP)电话、多媒体分发(multi-media distribution)、游戏以及监视系统等领域.将WLAN集成到手机里的需求正不断高涨,但手机同时还必须兼备游戏、PDA、数字相机、用于电邮和网络浏览的通用分组无线服务(general packet radio services,GPRS)、全球定位系统(global positioning system,GPS)以及蓝牙(Bluetooth)应用等众多功能.表1列出了目前被集成到手持式设备中的各种无线服务和其工作频带.     

A three-dimensional parabolic equation applied to VHF/UHFpropagation over irregular terrain

The two-dimensional (2-D) parabolic equation (PE) is widely used for making radiowave propagation predictions in the troposphere. The effects of transverse terrain gradients, propagation around the sides of obstacles, and scattering from large obstacles to the side of the great circle path are not modeled, leading to prediction errors in many situations. In this paper, these errors are addressed by extending the 2-D PE to three dimensions. This changes the matrix form of the PE making it difficult to solve. A novel iterative solver technique, which is highly efficient and guaranteed to converge, is presented. In order to confine the domain of computation, a three-dimensional (3-D) rectangular box is placed around the region of interest. A new second-order nonreflecting boundary condition is imposed on the surface of this box and its angular validity is established. The boundary condition is shown to keep unwanted fictitious reflections to an acceptable level in the domain of interest. The terrain boundary conditions for this 3-D PE method are developed and an original technique for incorporating them into the matrix form of the iterative solver is described. This is done using the concept of virtual field points below the ground. The prediction accuracy of the 3-D PE in comparison to the 2-D PE is tested both against indoor scaled frequency measurements and very high frequency (VHF) field trials