英文翻译外文文献翻译23毕业设计外文英文翻译射频与微波应用.doc

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1、附录A 英文原文Radio Frequency and Microwave ApplicationsA.1 IntroductionThis chapter lays the foundation for understanding higher-frequency wave phenomena and divides the task of active circuit design for RE/MV frequencies into specific concept blocks. These concept blocks create a gradual approach to und

2、erstanding and designing RF/MW circuits and represent specific realms of knowledge that need to be mastered to become an accomplished designer.Before we describe and analyze these types of waves we need to consider why RF/microwaves as a subject has become so important, that it is placed at the fore

3、front of our modern technology. Furthermore, we need to expand our minds to the many possibilities that these signals can provide for peaceful practices by exploring various commercial applications useful to mankind.A 1.1 A Short History of RF and MicrowavesCirca 18641873, James Clark Maxwell integr

4、ated the entirety of mans knowledge of electricity and magnetism by introducing a set of four coherent and self-consistent equations that describe the behavior of electric and magnetic fields on a classical level. This wav the beginning of microwave engineering, as presented in a treatise by Maxwell

5、 at that time .He predicted, purely from a mathematical standpoint and on a theoretical basis, the existence of electromagnetic wave propagation and that light was also a from of electromagnetic energy both completely new concepts at the time.From 1885 to 1887, Oliver Heaviside simplified Maxwells w

6、ork in his published papers. From 1887 to 1891, a German physics professor, Heinrich Hertz, verified Maxwells predictions experimentally and demonstrated the propagation of electromagnetic wave. He also investigated wave propagation phenomena along transmission line and antennas and developed severa

7、l useful structures. He could be called the first microwave engineer.Marconi tried to commercialize radio at a much lower frequency for long-distance communications, but as he had a business interest in all of his work and developments, this was not a purely scientific endeavor.Neither Hertz nor Hea

8、viside investigated the possibility of electromagnetic wave propagation inside a hollow metal tube because it was felt that two conductors were necessary for the transfer of electromagnetic wave or energy. In 1897, Lord Rayleigh showed mathematically that electromagnetic wave propagation was possibl

9、e in wave-guides, both circular and rectangular. He showed that there are infinite sets of modes of the TE and TM type possible, each with its own cut-off frequency. These were all theoretical predictions with no experimental verifications.From 1897 to 1936, the wave-guide was essentially forgotten

10、until two men, George Southworth (AT&T) and W. L. Barron (MIT), who showed experimentally that a wave-guide could be used as small bandwidth transmission medium, capable of carrying high power signals.With the invention of the transistor in the 1950s and the advent of microwave integrated circuits i

11、n the 1960s, the concept of a microwave system on a chip became a reality. There have been many other developments, mostly in terms of application mass, that have made RF and microwave an enormously useful and popular subject. Maxwells equations laid the foundation and laws of the science of electro

12、magnetic, of which the field of RF and microwave is a small subset. Due to the exact and all-encompassing nature of these laws in predicting electromagnetic phenomena, along with the great body of analytical and experimental investigations performed since then, we can consider the field of RF and mi

13、crowave engineering a “mature discipline” at this time.A.1.2 Applications of Maxwells Equations As indicated earlier in Chapter 2, Fundamental Concepts in Electrical and Electronics Engineering, standard circuit theory can neither be use at RF nor particularly at microwave frequencies. This is becau

14、se the dimensions of the device or components are comparable to the wavelength, which means that phase of an electrical signal (e.g., a current or voltage) changes significantly over the physical length of the device or component. Thus use of Maxwells equations at these higher frequencies becomes im

15、perative. In contrast, the signal wavelengths at lower frequencies are so much larger than the device or component dimensions, that these are negligible variation in phase across the dimensions of the circuit. Thus Maxwells equations simplify into basic circuit theory, as covered in Chapter 3, Mathe

16、matical Foundation for Understanding Circuits. At the other extreme of the frequency range lies the optical field, where the wavelength is much smaller than the device or circuit dimensions. In this case, Maxwells equations simplify into a subject commonly referred to as geometrical optics, which tr

17、eats light as a ray traveling on a straight line. These optical techniques may be applied successfully to the analysis of very high microwave frequencies (e.g., high millimeter wave range),where they are referred to as “quasi-optical.” Of course, it should be noted that further application of Maxwel

18、ls equation leads to an advanced field of optics called “physical apices or Fourier optics,” which treats light as a wave and explains such phenomena as diffraction and interference, where geometrical optics fails completely. The important conclusion to be drawn from this discussion is that Maxwells

19、 equations present a unified theory of analysis for any system at any frequency, provided we use appropriate simplifications when the wavelengths involved are much larger, comparable to, or much smaller than the circuit dimensions.A.1.2 Properties of RF and Microwaves An important property of signal

20、s at RF, and particularly at higher microwave frequencies, is their great capacity to carry information. This is due to the large bandwidths available at these high frequencies. For example, a 10 percent bandwidth at 60MHz carrier signal is 6MHz, which is approximately one TV channel of information;

21、 on the other hand 10 percent of a microwave carrier signals at 60 GHz is 6GHz, which is equivalent to 1000 TV channels. Another property of microwaves is that they travel by line of sight, very much like the traveling of light rays, as described in the field of geometrical optics. Furthermore, unli

22、ke lower-frequency signals, microwave signals are not bent by ionosphere. Thus use of line-of-sight communication towers or links on the ground and orbiting satellites around the globe are a necessity for local or global communications. A very important civilian as well as military instrument is rad

23、ar. The concept of radar is based on radar cross-section which is the effective reflection area of the target. A targets visibility greatly depends on the targets electrical size, which is a function of the incident signals wavelength. Microwave frequency is the ideal signal band for radar applicati

24、ons. Of course, another important advantage of use of microwaves in radars is the availability of higher antenna gain as the frequency is increased for a given physical antenna size. This is because the antenna gain being proportional to the electrical size of the antenna becomes larger as frequency

25、 is increased in the microwave band. The key factor in all this is that microwave signal wavelengths in radars are comparable to the physical size of the transmitting antenna as well as the target. There is a fourth and yet very important property of microwaves; the molecular, atomic, and nuclear re

26、sonance of conductive materials and substances when exposed to microwave fields. This property creates a wide variety of applications. For example, because almost all biological units are composed predominantly of water and water is a good conductor, microwave technology has tremendous importance in

27、 the fields of detection, diagnostics, and treatment of biological problems or medical investigations (e.g., diathermy, scanning, etc.). There are other areas in which this basic property would create a variety of applications such as remote sensing, heating (e.g., industrial purification and cookin

28、g) and many others are listed in a later section.A.2 Reasons for Using RF/MicrowavesOver the past several decades, there has been a growing trend toward use of RF/microwaves in system applications. There are many reasons among which the following are prominent:Wider bandwidths due to higher frequenc

29、ySmaller component size leading to smaller systemsMore available and less crowded frequency spectrumLower interference due to lower signal crowdingHigher speed of operationHigher antenna gain possible in a smaller spaceOn the other hand, there are some disadvantages to using RF/microwaves, such as:

30、more expensive components, availability of lower power levels, existence of higher signal losses, and use of high-speed semiconductors (such as GaAs or INP) along with their corresponding less-mature technology (relative to the traditional silicon technology, which is now quite mature and less expen

31、sive). In many RF/microwave applications the advantages of a system operating at these frequencies outweigh the disadvantages and propel engineers to a high-frequency design.A.3 RF/Microwave ApplicationsThe major applications of RF/microwave signals can be categorized as follows:A.3.1 CommunicationT

32、his application includes satellite, space, long-distance telephone, marine, cellular telephone, data, mobile phone, aircraft, vehicle, personal, and wireless local area network (WLAN), among others. Two important subcategories of applications need to be considered: TV and radio broadcast, and optica

33、l communications.TV and radio broadcastIn this application, RF/microwaves are used as the carrier signal for audio and video signals. An example is the Direct Broadcast System (DBS), which is designed to link satellites directly to home users.Optical communicationsIn this application, a microwave mo

34、dulator is used in the transmitting side of a low-loss optical fiber with a microwave demodulator at the other end. The microwave signal acts as a modulating signal with the optical signal as the carrier. Optical communication is useful in cases where a much larger number of frequency channels and l

35、ess interference from outside electromagnetic radiation are desired. Current applications include telephone cables, computer network links, low-noise transmission lines, and so on.A.3.2 RadarThis application includes air defense, aircraft/ship guidance, smart weapons, police, weather, collision avoi

36、dance, and imaging.A.3.3 NavigationThis application is used for orientation and guidance of aircraft, ships, and land vehicles. Particular applications in this area as follow:Microwave Landing System (MLS), used to guide aircraft to land safely at airportsGlobal Positioning System (GPS), used to fin

37、d ones exact coordinates on the globeA.3.4 Remote Sensing In this application, many satellites are used to monitor the globe constantly for weather conditions, meteorology, ozone, soil moisture, agriculture, crop protection from frost, forests, snow thickness, icebergs, and other factors such as mon

38、itoring and exploration of natural resources.A.3.5 Domestic and industrial ApplicationsThis application includes microwave ovens, microwave clothes dryers, fluid heating systems, moisture sensors, tank gauges, automatic door openers, automatic toll collection, highway traffic monitoring and control,

39、 chip defect detection, flow meters, power transmission in space, food preservation, pest control, and so onA.3.6 Wireless ApplicationsShort-distance communication inside as well as between buildings in a local area network (LAN) arrangement can be accomplished using RF and microwaves. Connecting bu

40、ildings via cables (e.g., coax or fiber optic) creates serious problems in congested metropolitan areas because the cable has to be run underground from the upper floors of one building to the upper floors of the other. This problem, however, can be greatly alleviated using RF and microwave transmit

41、ter/receiver systems that are mounted on rooftops or in office windows. Inside buildings, RF and microwaves can be used effectively to create a wireless LAN in order to connect telephones, computers, and various LANs to each other. Using wireless LANs has a major advantage in office rearrangement wh

42、ere phones, computers, and partitions are easily moved with no change in wiring in the wall outlets. This creates enormous flexibility and cost savings for any business entity.附录B 中文翻译射频与微波应用B.1 引言本章为理解更高频率的颠簸现象奠定了基础，这里我们将射频/微波频端的有源电路的设计分为不同的概念模块，他们以循序渐进的方式出现，以便我们理解和设计射频/微波电路，并且该部分内容也是一个熟练设计的人员所必须掌握

43、的知识领域。 在讲述这类电波之前，需要考虑这样一个问题：为什么射频/微波变得如此重要，以至于人们要将其归入现代技术的前沿科学？此外，通过研究该学科有益人类的各种商业应用，我们必须开拓思路，探索将微波信号用于和平用途的各种可能性。B.1.1 射频和微波简史大约从1864年到1873年间，詹姆士克拉克麦克斯韦将人类所掌握的电磁学知识归结为一组由四个一致相干的方程构成的方程组，以次描述经典电磁场的特性。正如麦克斯韦当时所讲，这是微波工程学的开始。他还以纯数学观点从理论上预言存在电磁波传播现象，以及光也是电磁波的一种形式，这在当时是全新的概念。从1885年到1887年尖，奥利弗海维赛德在其发表的论文中

44、将麦克斯韦方程进一步简化。从1887年到1891年尖，德国物理学教授赫兹通过实验并演示了麦克斯韦关于电磁波传播现象的预言。他还研究了传输线和天线中的颠簸传输现象，提出了几种有用的结构。他应该算是最早的微波工程师。接下来，马可尼试图以更低的频率实现长距离通信，并使之商品化，但由于他所有的工作都涉及到商业利益，所以这不是纯科学行为。赫兹和海维赛德都没有考察电磁波在真空管中传播的可能性，因此当时人们认为电磁波或电磁能的转换必须需要两种导体才能进行。1897年，瑞利从数学上证明电磁波也可以在圆形和方形的波导中传播，无论是横波颠簸还是横磁波，都存在无穷多种可能的模式，每一种都有自己特定的截止频率。但所有

45、这些都只是理论上的推测，尚未被实验验证。从1897年到 1936年，正当人们差不多已忘记波导时，AT&T乔治Southworth和MIT的Barron再次想到它，通过实验证明波导可用做低带宽的传输介质，这就意味着它能够携带大功率信号。随着20世纪50年代晶体管的发明和60年代微波集成电路的出现，芯片级微波系统的设想已经变成了事实。适应于当时应用的需要，还有许多其他的发展。所有这些，都使得射频/微波成为一个非常有用和热门的研究领域。麦克斯韦方程为电磁学理论奠定了基础，而射频/微波只是这个领域中很小的一个分支。由于麦克斯韦定律可能准确预测各种电磁现象，加之后续进行的大量的理论分析和实验研究工作，可

46、以说射频/微波工程是一门成熟的学科。B.1.2 麦克斯韦方程的应用基本电路理论对射频，尤其微波频段不适用。这是因为元件的尺寸和波长具有可能性，这意味着，电信号（电流或电压）的相位将会随着所通过的设备或元器件的尺寸显著变化。于是，人们迫切需要将麦克斯韦方程应用于这些更高的频段。当信号频率很低以至于其波长比元器件尺寸大得多时，电路上的相位变化可以近似忽略。这时麦克斯韦方程就简化为基本电路理论。当信号频率很高以至于波长要比器件或电路尺寸小很多时，对应频率轴上另一端的光场。此时，麦克斯韦方程可简化为通常所说的集合光学，它将光视为沿直线传播的射线。以上光学方法可成功运用于高频微波分析，这时称其为“准光学

47、”。麦克斯韦方程的进一步运用导致光学中一个新领域的出现，称作“物理光学”或者“傅里叶光学”，它将光看成是一种波，这就很好地解释了传统几何光学所不能解释的光的衍射和干涉现象。从以上讨论中可得如下重要结论：当系统的波长与电路尺寸相比大得多、小得多或者可比拟时，只要进行适当的简化，麦克斯韦方程就可对任何频率下的任何系统提供统一的分析理论。B.1.3 射频/微波特性无线电信号，特别是高频信号的一个显著特点是它能携带大量的信息，这得益于高频所提供的较宽的带宽。例如，60MHz的载波信号的10%带宽是6MHz，这近似于一个电视频道；而60GHz载波信号的10%是6GHz，这等效于一千个电视频道。微波的另一

48、个特征是按视线传播，这和几何光学中光的传播方式非常相似。此外，与低频信号不同，微波信号不会经电离层弯曲或反射。因此，在本地或全球通信中，必须在地面上或绕地球运转的卫星上安装实现通信塔。雷达是很重要的军民两用设备，它主要依靠雷达截面，即目标的有效反射面积来发现目标，微波段是使用雷达的理想频段。目标能否发现，很大程度上取决于目标的电学尺寸，它是入射信号的波长的函数。在雷达中使用微波的另一个优点是：给定天线尺寸后，增大信号频率可以获得更大的天线增益，这是因为天线的增益与天线的电尺寸成正比，在微波频段随着频率的增大而增大。其中的关键因素是雷达中所用微波信号的波长与发射天线及目标尺寸可相比拟。微波的第四个，也是非常重要的一个特性是：处于微波场中的分子、原子能共振，这一特性可用于许多方面。例如，几乎所有的生物体都主要由水构成，而水是一种导体，所以微波技术在检测、诊断、处理生物学问题及医学研究（如透热疗法，扫描）方面都有着重要的应用。还有一些其他的领域，例如遥感，加热（工业提纯和烹饪等）等，这些都将在下一节中介绍。1 使用射频/微波的理由在过去的几十年间，逐渐趋于使用射频/微波系统，主要原因如下：高频率，宽带宽元器件小，系统小充裕的可用频率用于雷达的波长短，分辨率高信号无阻塞，干扰小工作速度快小范