专业外语电磁波传播第9讲

1、编辑pptLecture 9 Electromagnetic Wave Propagation (I)编辑ppt编辑ppt-通信、广播载波的产生、辐射、传播、接收和传输 天线和收发和传输设备的设计、射频信道的分析计算 如：移动通信、卫星通信、微波中继通信、无线接入网 无线局域网、光纤通信、电视广播等-雷达探测与反探测技术 各种雷达高性能天线和收发设备的设计、目标识别、成象 隐身设计-电磁兼容和抗干扰 设计电子器件、电路和系统是相互之间干扰最小编辑ppt 国防领域：电磁炸弹和电磁炸弹防护 医疗领域：微波治疗 食品： 微波炉，灭菌 商业： 射频识别IC卡 .编辑ppt卫星通信地球站天线系统卫星通信

2、地球站天线系统极轨卫星跟踪极轨卫星跟踪接收天线接收天线 卫星通信地球站 编辑ppt编辑ppt编辑ppt编辑pptGround-Wave Propagation 地波：沿地球表面空间向外传播 无线电波。Space-Wave Propagation 空间波：象光线一样沿直线传播的无线电波，又称为视波。Sky-Wave Propagation 天波：利用电离层的反射来传播无线电波。propagation prpgein 编辑ppt编辑pptrefraction rifrkn reflection riflekninterference intfirns编辑pptpower line interfer

3、ence 电力线干扰power-supply interference 电源干扰intermodulation interference 互调干扰inter symbol interference 符号间干扰, 码间干扰inverse mixture interference 倒向混频干扰编辑pptadjacent-channel interference 邻信道干扰atmospheric interference 天电干扰audio interference 声频信号干扰radio interference 射电干扰, 无线电干扰snow interference “雪花”干扰adjacen

4、t deisnt 临近的编辑pptmirror interference 镜像干扰multipath interference 多径干扰noise interference 噪声干扰background interference 背景干扰image frequency interference 像频干扰编辑pptharmonic interference 谐波干扰hum interference 交流声干扰broad band interference 宽带干扰broadcast interference 广播干扰back door interference 后门干扰编辑pptcolour s

5、ubcarrier interference 彩色副载波干扰common mode interference 共模干扰continuous wave interference 连续波干扰crosstalk interference 交叉干扰, 串话干扰electromagetic interference 电磁干扰beat interference拍频干扰编辑ppt10.1 Introduction 编辑ppt An electromagnetic wave contains an electronic field and a magnetic field at 90to each other

6、. The polarization of a plane electromagnetic wave is simply the orientation of the electric field vector in respect to the surface of the Earth (i.e., looking at the horizon). If the polarization remains constant, it is described as linear polarization. Horizontal polarization and vertical polariza

7、tion are two forms of linear polarization. If the electric field is propagating parallel to the Earths surface, the wave is said to be horizontally polarized. If the electric field is propagating perpendicular to the Earths surface, the wave is said to be vertically polarized. If the polarization ve

8、ctor rotates 360as the waves moves one wavelength through space and the field strength is equal at all angles of polarization , the wave is described as having circular polarization. When the field strength varies with changes in polarization, this is described as elliptical polarization. A rotating

9、 wave can turn in either direction. If the vector rotates in a clockwise direction, it is right-handed , and if the vector rotates in a counter-clockwise direction, it is considered left-handed. 编辑ppt参考译文:编辑pptdestination n.目的地polarization n.物偏振(现象),极化(作用),两极化,分化polarize v.(使)偏振, (使)极化, (使)两极分化plane

10、 electromagnetic wave 平面电磁波orientation n.方向, 方位vector n.数向量, 矢量, 带菌者编辑ppthorizon n.地平(线),(知识,思想等的)范围,视野parallel adj.平行的, 类似的, 并联的n.平行线,类似, 相似物v.相应, 平行perpendicular adj.垂直的, 正交的n.垂线rotate v.(使)旋转counter-clockwise 逆时针方向编辑ppt In Electronic communications systems, sometime it is impractical or impossibl

11、e to interconnect two pieces of equipment with a physical facility such as a metallic wire or cable. This is especially true when the equipment is separated by large span of water, rugged mountains, or harsh desert terrain, or when communicating with satellite transponders orbiting 22,000 miles abov

12、e Earth. Also, when the transmitters and receivers are mobile, as with two-way radio communications and mobile telephone, providing connections with metallic facilities is impossible. Therefore, free space or Earths atmosphere is often used as a transmission medium.编辑pptFacility n. 设备 fsilitirugged

13、adj.高低不平的 harsh adj.粗糙的, 荒芜的terrain n.地形transponder n.卫星转发器rgidtrnspnd 编辑ppt参考译文:编辑ppt Free-space propagation of electromagnetic waves is often called radio frequency (RF) propagation or simply radio propagation. Although free space implies a vacuum, propagation through Earths atmosphere is often re

14、ferred to as free-space propagation and can often be treated as just that. The primary difference being that Earths atmosphere introduces losses to the signal that are not encountered in a vacuum. Electromagnetic waves will propagate through any dielectric material, including air. Electromagnetic wa

15、ves, however, do not propagate well through lossy conductors, such as sea water, because the electric fields cause currents to flow in the material that rapidly dissipate the waves energy. 编辑pptvacuum n.真空 adj.真空的loss n.损失，遗失，丧失dielectric adj. 绝缘的 dissipate v.消散 disipeitvkjum daiilektrik 编辑ppt Radio

16、 waves are electromagnetic waves and. like light, propagate through free space in straight line with a velocity of 300 000 000 meters per second. Other forms of electromagnetic waves include infrared, ultraviolet. X rays, and gamma rays. To propagate radio waves through Earths atmosphere, it is necessary that the energy be radiated from the source, then the energy must be captured at the receive en