1.射频无线通信系统介绍

1、实用标准文案1 .射频和无线通信系统介绍概述This tutorial is part of the National Instruments Measurement Fundamentals series. Each tutorial in this series teaches you a specific topic of common measurement applications by explaining the theory and giving practical examples. This tutorial covers an introduction to RF, wi

2、reless, and high-frequency signals and systems.本教程是测量NI基础系列的一部分。本系列教程中的每一个指南结合理论解释和实际的例子教你常用的 测量应用。本教程介绍介绍了射频，无线和高频信号与系统。For the complete list of tutorials, return to the NI Measurement Fundamentals Main page, or for more RF tutorials, refer to the NI RF Fundamentals Main subpage.对于教程的完整1#单，请返回NI Me

3、asurement Fundamentals Main page ,或更多的射频教程,请参阅 NI RF Fundamentals Main subpage .目录1. Marconi and the First Wireless Transmissions马可尼和第一次无线传输2. What is RF? 射频是什么？3. Why Operate at Higher Frequencies?为什么工作在更高的频率？4. Frequency Shifting through Frequency Mixing通过混频移频5. Looking for more RF Basics? 寻找更多的射频

4、基础知识？6. Relevant NI Products7. Conclusions 结论Marconi and the First Wireless TransmissionsRadio Frequency (RF) and wireless have been around for over a century with Alexander Popov and Sir Oliver Lodge laying the groundwork for Guglielmo Marconi' s wirelessradio developments in the early 20th cen

5、tury. In December 1901, Marconi performed his most prominent experiment, where he successfully transmitted Morse code from Cornwall, England, to St John ' s, Canada.在亚历山大波波夫爵士和奥利弗洛奇奠定了20世纪初马可尼无线电台的基础时，射频(RF)和无线已经出现了一个世纪。在 1901年12月，马可尼进行他最杰出的实验，在那里他成功从英国康沃尔发送莫尔斯 码到加拿大圣约翰。What is RF? 什么是射频？RFitsel

6、f has becomesynonymous with wireless and high-frequency signals, describing anything from AM radio between 535 kHz and 1605 kHz to computer local area networks(LANs) at 2.4 GHz. However, RF has traditionally defined frequencies from a few kHzto roughly 1 GHz. If one considers microwave frequencies a

7、s RF, this range extendsto 300 GHz. The following two tables outline the various nomenclatures for the frequency bands. The third table outlines some of the applications at each of the various frequency bands.RF本身已成为无线和高频信号的代名词，它包括了 535kHz7605kHz的调幅无线电至IJ 2.4 GHz的计算机局域网(LAN之间的任何频率。然而，传统定义的RF从几kHz的频率

8、至大约1GHz如果把微波频率考虑作为射频，这个范围扩展到 300GHz以下两个表概述了各频段的术语。第三表列出了在不同频段的一些应用。Table 1: Frequency Band DesignationsfkBandDescripLidn对 300 Hz伊 kmELFElreniely kw frequency300-30()0 HzlO,-MP kmVFYoicd ftequency3-30 kHz100-10 kmVLFVrn' lenv 1 req u cncy50- 300 kHz10-1 kmLFLow 1 reQue ncs03-3 MHz14),1 tmMFMedium

9、 trcqucncy3-30 MHz100 10 mHFHiyh IrequcncyM-3(X MHz10-1 mYHFVery high IrequcncylOCUlOtmUHFUltra-high fieqi叱ncy3-30 GHz10-1 cmSHFSuperhigh frequency30-3CH1 GHz1 1-1 mmEHFExtreme y high frcquciicvimillimeier Wiives；Table 1 shows a relationship between frequency (f) and wavelength (入).A wave or sinusoi

10、d canbe completely described by either its frequency or its wavelength. They are inversely proportional to each other and related to the speed of light through a particular medium. The relationshipin a vacuum is shown in the following equation:where c is the speed of light. As frequency increases, w

11、avelength decreases. For reference, a 1 GHz wave has a wavelength of roughly 1 foot, and a 100 MHz wave has a wavelength of roughly 10 feet.表1显示了频率（f）和波长（入）的关系。波或正弦波可以完全由其频率或波长描述。他们成反比关系，并与通过特定媒介的光速有关。在真空的关系如公式如下：二三了以。其中c是光速。随着频率的增加，波长减小。作为参考，1 GHz的波具有波长约为1英尺，100 MHz的波有大约10英尺的波长。Table 2: Microwave L

12、etter Band Designations/ (GHz)Ltiikr Band Dtjsiginnuin2T 4 87工4I2.4-1K18-26.526.5-4(1L bainJS btindC handX band Ku bandK bandKa handTable 3: Frequency Applications and Allocations in the U.S.AllijcaLrd PurposesFrequencies in kHz490 5】。510-535535-1605 1605-1750 15100-20()0Distress (telegraph)Govemnic

13、ntAM radio“nd/m讣bile public safely1Amateur radioFrequencirs iti M Hz26.96 -27,23, 462,525-46747550.56- 32, 33-3% 35-33, 39-40,40.02-40.9H41.015*6. 47TW 773, 74-74fit 75J 76, 150,05 156.2475 157J875-161.575. 162.0125-173.4220-222,421-430, 451-454 456-459. 460-512746-824, R51T69,豹6 901, 935-94074.8- 7

14、5.2, KB-137, 32B.63SS.4, 1；60-1215, J427-1525, 230 2290. 2310-2320. 2345-2390162.012ST7T250-5% 144-I4K 216-220, 222-225; 420-450, 902-928. 1240 1300:300 2301 2390 245072-73t 75.2-76, 2m954-72, 76-89, 174 21a 470-60KR8-99t 1 (JO-108824 849185(1-1990。T9边239J24GO1215-1240, 135ft 140al 559-1610Frequenci

15、es in GHz0.216-0J3D, 0.235-0J67. 0.4061-0.45, 0.902- 092& 0+96(J-l,215h 1215-2,229,2320- 234sl 2360-2390, 27-11, 31-3,7, 5.0547, 5.6-5925, 85-10, 10J0-1045, 10-510.5J 13JS-I3.73, 14-l42t 15.4-16.6, 172- 】77 24.05 24.45. 33 4 36. 45 #9 59 64. 66-713 76-77. 92-1002,390-2.400 2.40 -2.4H35 45559, 76

16、-77, 95-100 L* 142 10.57035, 24.05-24J5 0.902TL92s. 2.4-25. 5.85-55Alicea led PurposesClli/en band radiosPrivate mtibil radio (taxis. Irucks. busek railroads)Avuilimi (communicution “nd radar)Vtihidd recovery LoJack；Amateur radioRfldio Lonlrol (petstinal)Tclrvision brcmdLAisling VHF 4ndUHFEM India h

17、roLidaistingCulloliir ielcphonci'erstmal c<)inin uni canonsPcrsiJixal coinin, (uuliuoiscd ：Ijlokil PotJliuninit Sv31cmM (GPS) Allocated PurposesRadiir. all typesLANs (untcensed)MkMDwave ovensVehicle, aniicdliskm. iKivigadonPolice speed radartadio li equunc、idenliBcalim"!(RFID)Geostationa

18、iy salellilt with lixed earth reuavers74.9- IL7T22 142143, 17.7-此队 27.529 ls 2905-30,40.5-41A 49.2-50.2NtxieosLuiLunary salelliies. mobile receivers (big LEO. global phoneiUnliccnscd indnstriul. scicnLifie, and medical connnurHcatioti device!Amagr radioCable leleisioD rdayLocal multipoini TV discrib

19、uiionDirect broadcast TV ffr&nl iulel- li院)Fixed micruNHt七public and pri- vuic;J.6W -1626.3,24835-2.5. 5.091- 525. 6.77.075, 15.43-15.630,0407, 902-92K, 245 J25叫 5,725- 5.S75, 24 2415, 59 599 60-64, 713r72, 03.5-104, U6J-117t 122-125, 126.5-127, 152.5-153, 24424633-5.5, 5.655,925. 10-10.5. 224,2

20、5.47- 47.264256.525, 1 工 7-13,25, 1916-19.7,31-313 27.5293122-12.7, 24.75-25.05. 25.05-25250.928 4),929. 0,932 0.935,0.941- 0960, "501.990, 2J 1-2,20： 2.45忆26吸7<2,5.925 6g 10.55-1。典 10.7-13.25. 14, 14A 17J-J9.7, 21.2-23,6. 27.55-29.5, 3131.3, 38.6 40RF measurement methodology can generally b

21、e divided into three major categories: spectral analysis, vector analysis, and network analysis. Spectrum analyzers, which provide basic measurement capabilities, are the most popular type of RF instrument in many general-purpose applications. Specifically, using a spectrum analyzer you can view pow

22、er-vs-frequency information, and can sometimes demodulate analog formats, such as amplitude modulation (AM), frequency modulation (FM), and phase modulation(PM).Vector instruments include vector or real-time signal analyzers and generators. These instruments analyze and generate broadband waveforms,

23、 and capture time, frequency, phase, and power information from signals of interest. These instruments are much more powerful than spectrum analyzers and offer excellent modulation control andsignal analysis.Network analyzers, on the other hand, are typically used for making S-parameter measurements

24、 and other characterization measurements on RF or high-frequency components. Network analyzers are instruments that correlate both the generation and analysis on multiple channels but at a much higher price than spectrum analyzers and vector signal generators/analyzers.射频测量方法大致可以分为三大类：频谱分析，矢量分析和网络分析

25、。频谱分析仪，它提供基本的测量功能，在许多通用应用中是最受欢迎的RF仪器类型。具体来说，使用频谱分析仪可以查看功率与频率的信息，有时可以解调模拟格式，如调幅（ AM ,调频（FM和相位调制（PM 。矢量仪器包括矢量或实时信号分析仪和发生器。这些仪器分析和产生宽带波形，并从感兴趣的信号捕获时 间，频率，相位，功率信息。这些仪器比频谱分析仪功能强大，提供优良的调制控制和信号分析。网络分析仪通常用于射频或高频元件的S-参数测量及其他特性的测量。网络分析仪通过多通道融合了信号产生和信号分析，但是它的价格比频谱分析仪和矢量信号发生器/分析仪要高。Why Operate at Higher Frequen

26、cies?为什么工作在更高的频率？From Table 3 we notice that the frequency spectrum is quite fragmented and dense.This encompassesone of the reasons that we are constantly pushing applications into higher and higher frequencies. However, someof the other reasons accounting for this push into higher frequencies incl

27、ude efficiency in propagation, immunity to some forms of noise and impairments as well as the size of the antenna required. The antenna size is typically related to the wavelength of the signal and in practice is usually ? wavelength.This leads to a very interesting question. Typically, data is stru

28、ctured and easily represented at low frequencies; how can we represent it or physically translate it to these higher RF frequencies? For example, the human audible range is from 20 Hz to 20 kHz. According to the Nyquist theorem, we can completely represent the human audible range by sampling at 40 k

29、Hz or, more precisely, at 44.1 kHz (this is where stereo audio is sampled). Cell phones, however, operate at around 850 MHz. How does this happen?从表3中我们看到，频谱是相当分散，而且密度大。这也是我们之所以不断将应用推向更高的频率原因之 一。然而，其他因素造如传播效率，抗噪声干扰以及所需要的天线尺寸也将应用推向更高的频率。天线的 尺寸通常与信号的波长，在实践中通常是四分之一波长有关。这导致了一个很有趣的问题。通常，数据容易在低频率表示和结构化；我们

30、如何才能在频率较高的射频表示该信息或按自然规律翻译成较高的射频信息？例如，人类的听觉范围是从 20赫兹到20千赫。根据奈奎 斯特定理，我们可以完全通过在40千赫或者更准确地为 44.1千赫的进行采样来表示音频信息(这就是立体声音频米样)。然而手机工作在850兆赫。这是如何发生的？Frequency Shifting through Frequency Mixing通过混频移频Muchof the study of RFand high-frequencymeasurements occurs in the frequency domain.There is a duality between

31、the time-domain functions and those same functions represented in the frequency-domain. Figure 1 depicts frequency shifting the human audible range to transmit through cellular frequencies. The most common way to frequency shift is called mixing, which is equivalent to multiplying your signalbya sin

32、usoidal signal. The following mathematical trigonometric identity demonstrates this fact.,、co式毋i 一处一 COS(好i 十馅sm( X sm(5口上)=322Therefore, by beating two sine waves against each other, you get both sum and difference frequencies. You can shift an entire signal to a new frequency range(either up or downin spectrum) by selecting the appropriate value of -. In additio