电子信息工程专业英语翻译清华出版社EnglishforITandEE-03

Technical English,For Information Science and Electronic Engineering,Unit 3,EM Fields, Antenna and Microwaves,Part I,Electromagnetic Field,3,New Words,4,1,The electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. It is one of the four fundamental forces in the nature (the others are gravitation, the weak interaction, and the strong interaction),电磁场在空间无限延伸，并描述电磁相互作用。,5,2,The field can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. The way in which charges and currents interact with the electromagnetic field is described by Maxwells equations and the Lorentz force law.,电荷和电流与电磁场相互作用的方式由麦克斯韦方程组和洛伦兹力定律所描述。,6,3,From a classical point of view, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner, whereas from a quantum mechanical point of view, the field can be viewed as being composed of photons.,从经典的角度，电磁场可认为是光滑、连续的场，以波动方式传播；而从量子力学的角度，场可看作是由光子组成的。,7,4 Structure of the electromagnetic field,The electromagnetic field may be viewed in two distinct ways. Continuous structure: Classically, electric and magnetic fields are thought of as being produced by smooth motions of charged objects. For example, oscillating charges produce electric and magnetic fields that may be viewed in a “smooth”, continuous, wavelike manner.,例如，振荡电荷产生电场和磁场，可看成平滑的、连续的波动方式。,8,5,In this case, energy is viewed as being transferred continuously through the electromagnetic field between any two locations. For instance, the metal atoms in a radio transmitter appear to transfer energy continuously. This view is useful to a certain extent (radiation of low frequency), but problems are found at high frequencies (see ultraviolet catastrophe). This problem leads to another view.,The ultraviolet catastrophe, also called the Rayleigh-Jeans catastrophe, was a prediction of early 20th century classical physics that an ideal black body at thermal equilibrium will emit radiation with infinite power.,9,6,Discrete structure: The electromagnetic field may be thought of in a more “coarse” way. Experiments reveal that electromagnetic energy transfer is better described as being carried away in photons with a fixed frequency. Plancks relation links the energy E of a photon to its frequency n through the equation: E = h n,普朗克的关系式将光子的能量E及其频率n 通过下式联系起来,10,6,where h is Plancks constant, named in honor of Max Planck, and n is the frequency of the photon. For example, in the photoelectric effect the emission of electrons from metallic surfaces by electromagnetic radiation it is found that increasing the intensity of the incident radiation has no effect, and that only the frequency of the radiation is relevant in ejecting electrons.1,例如在光电效应中，即因电磁辐射而从金属表面发射电子的现象，我们发现增加入射辐射的强度并无影响，只有辐射频率与发射的电子有关。,11,7,This quantum picture of the electromagnetic field has proved very successful, giving rise to quantum electrodynamics, a quantum field theory describing the interaction of electromagnetic radiation with charged matter.,已经证明电磁场的量子描述是非常成功的，引出了量子电动力学，一种描述电磁辐射与带电物体之间的相互作用的量子场理论。,12,8 Dynamics of the electromagnetic field,In the past, electrically charged objects were thought to produce two types of field associated with their charge property. An electric field is produced when the charge is stationary with respect to an observer measuring the properties of the charge and a magnetic field (as well as an electric field) is produced when the charge moves (creating an electric current) with respect to this observer.,相对于测量电荷性质的观察者，电荷静止时产生电场，电荷运动（产生电流）时产生磁场（和电场）。,13,8,Over time, it was realized that the electric and magnetic fields are better thought of as two parts of a greater whole the electromagnetic field.2,随着时间的推移，人们认识到电场和磁场是电磁场这一整体的两个部分。,14,9,Once this electromagnetic field has been produced from a given charge distribution, other charged objects in this field will experience a force (in a similar way that planets experience a force in the gravitational field of the Sun). If these other charges and currents are comparable in size to the sources producing the above electromagnetic field, then a new net electromagnetic field will be produced.3,电磁场中其它带电体就会受到一个力的作用,如果另外这些电荷和电流的大小与产生上述电磁场的源是可比的，那么将产生一个新的净电磁场。,15,9,Thus, the electromagnetic field may be viewed as a dynamic entity that causes other charges and currents to move, and which is also affected by them. These interactions are described by Maxwells equations and the Lorentz force law.,电磁场可以认为是一个动力学实体，它促使其它电荷和电流运动，同时又受它们影响。,Part II,Microstrip Antenna,17,New Words,18,New Words,19,1,In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane.1,片状天线是一种窄带宽波束的天线，通过将天线单元图样蚀刻到粘贴在绝缘基底上的金属轨迹而制成，基底的另一面则粘贴连续的金属层形成接地平面。,20,1,Common microstrip antenna radiator shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas eschew a dielectric substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less robust but provides better bandwidth.,一些片状天线为了避免绝缘基底，在接地平面的上空用绝缘逆电流器悬挂一个金属贴片；这种结构的鲁棒性不是很好，但能提供更好的带宽。,21,1,Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.2,因为这种天线外形低矮，机械强度大，并且形状上适应性强，通常装在飞机或太空飞行器外表，或组合在移动无线电通信设备上。,22,2,Microstrip antennas are also relatively inexpensive to manufacture and design because of the simple 2-dimensional physical geometry. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonant frequency. A single patch antenna provides a maximum directive gain of around 6-9 dBi.,因为其简单的二维形状,dBi: decibel isotropic, the forward gain of an antenna compared with the isotropic antenna, which uniformly distributes energy in all directions.,23,2,It is relatively easy to print an array of patches on a single (large) substrate using lithographic techniques. Patch arrays can provide much higher gains than a single patch at little additional cost; matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches.,通过平板印刷技术我们很容易在单个大绝缘体上印刷贴片阵列。,用形成辐射电波的片状微带天线的同样机理，可对印刷微带天线的馈电结构进行匹配和相位调节。,24,2,The ability to create high gain arrays in a low-profile antenna is one reason that patch arrays are common on airplanes and in other military applications.,以低矮的天线构成高增益阵列的能力是片状天线广泛用于飞机和其他军事应用的原因之一。,25,3,The most commonly employed microstrip antenna is a rectangular patch. The rectangular patch antenna is approximately a one-half wavelength long section of rectangular microstrip transmission line. When air is the antenna substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength.,矩形贴片天线长近似为矩形微带传输线的一段，其长度等于半波长。,矩形微带天线的长度大约为自由空间波长的一半,26,3,Since the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. The resonant length of the antenna is slightly shorter because of the extended electric “fringing fields” which increase the electrical length of the antenna slightly.,天线的谐振长度略短一些，这是因为边缘场稍微增加了天线的电气长度。,Fringing fields: the electric fields produced by scattered electrons in an electron microscope.,27,3,An early model of the microstrip antenna is a section of microstrip transmission line with equivalent loads on either end to represent the radiation loss.,微带天线的一个早期模型是一段微带传输线，在一端具有等效负载，代表辐射损耗。,28,4,The dielectric loading of a microstrip antenna affects both its radiation pattern and impedance bandwidth. As the dielectric constant of the substrate increases, the antenna bandwidth decreases which increases the Q factor of the antenna and therefore decreases the impedance bandwidth.3,随着基底介电常数的增大，天线的带宽减小，其Q值提高，因而阻抗带宽减小。,29,4,This relationship did not immediately follow when using the transmission line model of the antenna, but is apparent when using the cavity model which was introduced in the late 1970s. The radiation from a rectangular microstrip antenna may be understood as a pair of equivalent slots.,当使用天线的传输线模型时这种情况并没有发生，到了七十年代后期出现空腔模型时这种情况就显现出来了。,30,4,These slots act as an array and have the highest directivity when the antenna has an air dielectric and decreases as the antenna is loaded by material with increasing relative dielectric constant.,这些狭缝就像一个阵列，当天线使用空气电介质时方向性最好，但是当天线的负载材料的相对介电常数增加时方向性会减弱。,31,5,An advantage inherent to patch antennas is the ability to have polarization diversity. Patch antennas can easily be designed to have various polarizations, using multiple feed points, or a single feed point with asymmetric patch structures.4 This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.,片状天线能很容易地通过多个馈点或具有非对称片结构的单一馈点设计成具有各种极化特性。,32,6,The half-wave rectangular microstrip antenna has a virtual shorting plane along its center. This may be replaced with a physical shoring plane to create a quarter-wavelength microstrip antenna. This is sometimes called a half-patch.,沿中心的虚拟短路平面,用物理短路平面替代上述虚拟短路平面就可以做成四分之一波长微带天线,33,6,The antenna only has a single radiation edge (equivalent slot) which lowers the directivity/gain of the antenna. The impedance bandwidth is slightly lower than a half-wavelength full patch as the coupling between radiating edges has been eliminated.,由于没有辐射边缘之间的耦合，所以阻抗带宽比半波长全贴片窄。,Part III,Microwaves,35,New Words,36,New Words,37,1,Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. Microwaves have wavelengths approximately in the range of 30 cm (frequency = 1 GHz) to 1 mm (300 GHz). This range of wavelengths has led many to question the naming convention used for microwaves as the name suggests a micrometer wavelength.1,这个波长范围已经使人对命名习惯提出了问题，因为微波使人联想到微米波长。,38,1,However, the boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The same equations of electromagnetic theory apply at all frequencies.,是相当随意的，在不同的学科领域有不同的用法,39,1,Apparatus and techniques may be described as “microwave” when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is no longer accurate.,信号的波长与设备的尺度大致相同,集总元件电路理论不再准确,40,1,The term microwave generally refers to “alternating current signals with frequencies between 300 MHz (3108 Hz) and 300 GHz (31011 Hz).” However, both IEC standard 60050 and IEEE standard 100 define “microwave” frequencies starting at 1 GHz (30 cm wavelength).,41,2,The existence of electromagnetic waves, of which microwaves are part of the frequency spectrum, was predicted by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region.,构建了在UHF频段产生和检测微波的装置，证明电磁波的存在,42,2, 3,In 1894 J. C. Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves. The microwave range includes ultra-high frequency (UHF) (0.33 GHz), super high frequency (SHF) (330 GHz), and extremely high frequency (EHF) (30300 GHz) signals.,微波传播的研究,43,4,Above 300 GHz, the absorption of electromagnetic radiation by Earths atmosphere is so great that it is effectively opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.,地球大气对高于300 GHz的电磁辐射的吸收是如此之大，以至于变得实际上是不透明，直到所谓的红外线和可见光窗口的频率范围，大气又变得透明。,44,5 Devices,Vacuum tube based devices operate on the ballistic motion of electrons in a vacuum under the influence of controlling electric or magnetic fields, and include the magnetron, klystron, traveling wave tube (TWT), and gyrotron.2,基于电子管的器件是在受控制电场和磁场影响的真空内由电子的冲击运动而工作的，包括磁控管，速调管，行波管和振动陀螺仪。,45,5,These devices work in the density modulated mode, rather than the current modulated mode. This means that they work on the basis of clumps of electrons flying ballistically through them, rather than using a continuous stream.3,这意味着它们是基于真空管发出的电子簇工作的，而不是用连续的电子流。,46,6 Uses,A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food. Water, fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating.,47,6,Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field induced by the microwave beam.,它们一端带正电，另一端带负电,它们力图与微波波束所引起的交变电场保持一致,48,6,This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion. Microwave heating is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate).,旋转分子撞击其它分子，使他们运动，这种分子运动产生热量。,微波加热对液态水是最有效的，其次为脂肪和糖类（分子偶极矩较少）以及冷冻水（分子不能自由转动）。,49,6,Microwave heating is sometimes incorrectly explained as a rotational resonance of water molecules: such resonance only occurs at much higher frequencies, in the tens of gigahertz. Moreover, large industrial/commercial microwave ovens operating in the 900 MHz range also heat water and food perfectly well.,微波加热有时被错误地解释为水分子的旋转共振，而这种共振只能发生在数十千兆赫的高频。,此外，大型工业/商业微波炉在900兆赫范围内工作，也能很好地加热水和食物。,50,7,A common misconception is that microwave ovens cook food from the “inside out”. In reality, microwaves are absorbed in the outer layers of food in a manner somewhat similar to heat from other methods. The rays from a microwave electrically manipulate water particles to cook food.,实际上与其它加热方法类似，微波被食物外层吸收。,51,7,It is actually the friction caused by the movement that creates heat and warms the food. The misconception arises because microwaves penetrate dry nonconductive substances at the surfaces of many common foods, and thus often deposit initial heat more deeply than other methods.,这种误解源自微波在许多普通食物的表面穿透干燥的非导电物质，因此比起其它方法来能在更深层堆积初始热量。,52,7,Depending on water content the depth of initial heat deposition may be several centimeters or more with microwave ovens, in contrast to broiling, which relies on infrared radiation, or the thermal convection of a convection oven, which deposit heat shallowly at the food surface.,使用微波炉，初始热沉积的深度可达几个公分以上，这取决于水分含量的多少,而焙烤是依赖红外辐射或烤箱内的热对流，它们在食物表面存储的热量很浅。,53,7,Depth of penetration of microwaves is dependent on food composition and the frequency, with lower microwave frequencies being more penetrating.,54,8,Microwave radio is used in broadcasting and telecommunication transmissions because, due to their short wavelength, highly directive antennas are smaller and therefore more practical than they would be at longer wavelengths (lower frequencies).,微波无线电用于广播和电信传输，这是因为其波长短，与波长较长时相比，方向性天线体积更小也更实用。,55,8,There is also more bandwidth in the microwave spectrum than in the rest of the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz while many GHz can be used above 300 MHz. Typically, microwaves are used in television news to transmit a signal from a remote location to a television station from a specially equipped van.,比起其它无线电波段，微波频谱有更宽的频带可以利用，频率低于300兆赫时可用带宽小于300兆赫，而在300兆赫以上可用频带达到几个GHz。,56,9,Before the advent of fiber optic transmission, most long distance telephone calls were carried via microwave point-to-point links through sites like the AT&T Long Lines facility. Starting in the early 1950s, frequency division multiplex was used to send up to 5,400 telephone channels on each microwave radio channel, with as many as ten radio channels combined into one antenna for the hop to the next site, up to 70 km away.4,20世纪50年代开始，人们用频分复用在每一个微波无线电信道中传送多达5400路电话，将10路无线电信道组合起来送到一个天线，发送到70公里以外的下一个中继站。,57,10,Radar also uses microwave radiation to detect the range, speed, and other characteristics of remote objects.,58,11,Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and UNII frequencies in the 5 GHz range. Licensed long-range (up to about 25 km) Wireless Internet Access services can be found in many countries (but not the USA) in the 3.5 4.0 GHz range.,经授权许可的远距离无线互联网接入业务,ISM bands: industrial, scientific and medical radio bands. UNII: Unlicensed National Information Infrastructure,59,12,Metropolitan Area Networks: MAN protocols, such as WiMAX (Worldwide Interoperability for Microwave Access) based in the IEEE 802.16 specification. The IEEE 802.16 specification was designed to operate between 2 to 11 GHz. The c