專業(yè)外語電磁波傳播第9講

1、編輯pptLecture 9 Electromagnetic Wave Propagation (I)編輯ppt編輯ppt-通信、廣播載波的產生、輻射、傳播、接收和傳輸 天線和收發(fā)和傳輸設備的設計、射頻信道的分析計算 如：移動通信、衛(wèi)星通信、微波中繼通信、無線接入網 無線局域網、光纖通信、電視廣播等-雷達探測與反探測技術 各種雷達高性能天線和收發(fā)設備的設計、目標識別、成象 隱身設計-電磁兼容和抗干擾 設計電子器件、電路和系統是相互之間干擾最小編輯ppt 國防領域：電磁炸彈和電磁炸彈防護 醫(yī)療領域：微波治療 食品： 微波爐，滅菌 商業(yè)： 射頻識別IC卡 .編輯ppt衛(wèi)星通信地球站天線系統衛(wèi)星通信

2、地球站天線系統極軌衛(wèi)星跟蹤極軌衛(wèi)星跟蹤接收天線接收天線 衛(wèi)星通信地球站 編輯ppt編輯ppt編輯ppt編輯pptGround-Wave Propagation 地波：沿地球表面空間向外傳播 無線電波。Space-Wave Propagation 空間波：象光線一樣沿直線傳播的無線電波，又稱為視波。Sky-Wave Propagation 天波：利用電離層的反射來傳播無線電波。propagation prpgein 編輯ppt編輯pptrefraction rifrkn reflection riflekninterference intfirns編輯pptpower line interfer

3、ence 電力線干擾power-supply interference 電源干擾intermodulation interference 互調干擾inter symbol interference 符號間干擾, 碼間干擾inverse mixture interference 倒向混頻干擾編輯pptadjacent-channel interference 鄰信道干擾atmospheric interference 天電干擾audio interference 聲頻信號干擾radio interference 射電干擾, 無線電干擾snow interference “雪花”干擾adjacen

4、t deisnt 臨近的編輯pptmirror interference 鏡像干擾multipath interference 多徑干擾noise interference 噪聲干擾background interference 背景干擾image frequency interference 像頻干擾編輯pptharmonic interference 諧波干擾hum interference 交流聲干擾broad band interference 寬帶干擾broadcast interference 廣播干擾back door interference 后門干擾編輯pptcolour s

5、ubcarrier interference 彩色副載波干擾common mode interference 共模干擾continuous wave interference 連續(xù)波干擾crosstalk interference 交叉干擾, 串話干擾electromagetic interference 電磁干擾beat interference拍頻干擾編輯ppt10.1 Introduction 編輯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. 編輯ppt參考譯文:編輯pptdestination n.目的地polarization n.物偏振(現象),極化(作用),兩極化,分化polarize v.(使)偏振, (使)極化, (使)兩極分化plane

10、 electromagnetic wave 平面電磁波orientation n.方向, 方位vector n.數向量, 矢量, 帶菌者編輯ppthorizon n.地平(線),(知識,思想等的)范圍,視野parallel adj.平行的, 類似的, 并聯的n.平行線,類似, 相似物v.相應, 平行perpendicular adj.垂直的, 正交的n.垂線rotate v.(使)旋轉counter-clockwise 逆時針方向編輯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.編輯pptFacility n. 設備 fsilitirugged

13、adj.高低不平的 harsh adj.粗糙的, 荒蕪的terrain n.地形transponder n.衛(wèi)星轉發(fā)器rgidtrnspnd 編輯ppt參考譯文:編輯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. 編輯pptvacuum n.真空 adj.真空的loss n.損失，遺失，喪失dielectric adj. 絕緣的 dissipate v.消散 disipeitvkjum daiilektrik 編輯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