专业外语电磁波传播第9讲

Lecture 9 Electromagnetic Wave Propagation (I) n n TextText n n BackgroundsBackgrounds n n Vocabulary Vocabulary n n Text TourText Tour n n 英译汉英译汉 n n 小作文小作文 BackgroundsBackgrounds 电磁场的典型应用电磁场的典型应用 -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 其它应用举例：其它应用举例： 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 . 卫星通信地球站天线系统 极轨卫星跟踪 接收天线 卫星通信地球站 terrestrial propagation of electromagnetic wavesterrestrial propagation of electromagnetic waves 陆地传播的电磁波陆地传播的电磁波 Ground-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 terrestrial propagation of electromagnetic terrestrial propagation of electromagnetic waveswaves陆地传播的电磁波陆地传播的电磁波 optical properties of radio waves optical properties of radio waves 无线电波的光学性质无线电波的光学性质 refraction 折射： 波穿过不同的介质的时候传播方向会发生 变化。 reflection 反射 diffraction 衍射：又称为绕射，光线照射到物体边沿后通过 散射继续在空间发射的现象。 interference 干涉：频率相同的两列波叠加，使某些区域的振 动加强，某些区域的振动减弱，而且振动 加强的区域和振动减弱的区域相互隔开。 refraction rifrkn reflection riflekn interference intfirns Interference in useInterference in use power line interference 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 Interference in useInterference in use adjacent-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 adjacent deisnt 临近的 Interference in useInterference in use mirror 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 Interference in useInterference in use harmonic 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 Interference in useInterference in use colour subcarrier 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 Text TourText Tour 10.1 Introduction An electromagnetic wave contains an electronic field and a magnetic field at 90to each other. 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 polarization 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 vector 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 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. Paragraph 1Paragraph 1 参考译文: VocabularyVocabulary destination 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 electromagnetic wave 平面电磁波 orientation n.方向, 方位 vector n.数向量, 矢量, 带菌者 VocabularyVocabulary horizon 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 In Electronic communications systems, sometime it is impractical or impossible 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 above 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. Paragraph 2Paragraph 2 VocabularyVocabulary Facility n. 设备 fsiliti rugged 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 rgid trnspnd 参考译文: 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 referred 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 waves, 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. Paragraph 3Paragraph 3 VocabularyVocabulary vacuum n.真空 adj.真空的 loss n.损失，遗失，丧失 dielectric adj. 绝缘的 dissipate v.消散 disipeit vkjum daiilektrik Radio waves are electromagnetic waves and. like light, propagate through free space in straight