研一課程考試微波測量基礎(chǔ)ch

1、第三章頻譜測量基礎(chǔ)OverviewWhat is Spectrum Analysis?8563ASPECTRUM ANALYZER 9 kHz - 26.5 GHz頻譜分析儀是研究電信號頻譜結(jié)構(gòu)的儀器，用于信號失真度、調(diào)制度、譜純度、頻率穩(wěn)定度和交調(diào)失真等信號參數(shù)的測量，可用以測量放大器和濾波器等電路系統(tǒng)的某些參數(shù)，是一種多用途的電子測量儀器。它又可稱為頻域示波器、跟蹤示波器、分析示波器、諧波分析器、頻率特性分析儀或傅里葉分析儀等?，F(xiàn)代頻譜分析儀能以模擬方式或數(shù)字方式顯示分析結(jié)果，能分析1赫以下的甚低 頻到亞毫米波段的全部無線電頻段的電信號。OverviewTypes of Tests Mad

2、e.MMoodduullaattiioonnDDiissttoorrttiioonnNNooiissee第三章 頻譜測量基礎(chǔ)3.8、頻譜儀使用注意事項3.7、頻譜儀基本操作3.6、頻譜儀誤差分析3.5、頻譜儀基本測量3.4、頻譜儀基本指標3.3、頻譜儀原理實現(xiàn)3.2、頻譜儀基本概念3.1、頻譜儀基礎(chǔ)信號分析波形信息幅度 周期 頻率幅頻信息頻率、功率諧波、雜波噪聲、失真矢量信息幅度誤差矢量誤差相位誤差調(diào)制域頻域時域3.1 頻譜分析儀基礎(chǔ)粗略掃中頻的頻譜監(jiān)視器掃本振的全景頻譜儀發(fā)展史智能頻譜分析儀多功能頻譜分析儀高性能頻譜分析儀微波通信網(wǎng)絡(luò)、導(dǎo)航、電子對抗頻譜儀主要用途頻率管理信號監(jiān)測3.1 頻譜

3、分析儀基礎(chǔ)信號頻域分析信號頻率 諧波分量信號功率寄生、交調(diào)信號邊帶時域分析信號周期升降沿峰值電壓OverviewDifferent Types of AnalyzersFourier AnalyzerParallel filters measuredAsimultaneouslyLCD shows full spectral displayf1f2fOverviewDifferent Types of AnalyzersSwept AnalyzerFilter 'sweeps' over rangeAof interestLCD shows full spectral disp

4、layf1f2f3.1 頻譜分析儀基礎(chǔ)信號時域與頻域的分析harmonic distortionoccupied bandwidthsignal stabilityoutput powerintermodulation distortionpower bandwidthcarrier-to-noise ratioAmplitude (power)時域測量頻域測量示波器方式頻譜分析方式時域頻域Nusoidal signal examined in the frequency左圖中的示波器顯示的正弦波實際上含有諧波成分。3.1 頻譜分析儀基礎(chǔ)模擬濾波器模數(shù)轉(zhuǎn)換器數(shù)字濾波器衰減器取樣器處理器顯示器A

5、F輸入fSFTDC頻譜分析儀動態(tài)信號分析儀信 號 頻 譜 分 析3.1 頻譜分析儀基礎(chǔ)V2窗口V1V3f1f2fs1fs2fs3頻譜分析儀動態(tài)信號分析儀信 號 頻 譜 分 析第三章 頻譜測量基礎(chǔ)3.8、頻譜儀使用注意事項3.7、頻譜儀基本操作3.6、頻譜儀誤差分析3.5、頻譜儀基本測量3.4、頻譜儀基本指標3.3、頻譜儀原理實現(xiàn)33.22、頻譜儀基本概念3.1、頻譜儀基礎(chǔ)頻譜分析儀基本概念f(a)輸入頻譜(b)屏幕譜線形狀(c)分辨力太低圖形掃 速靈敏度分辨率頻譜分析儀基本概念頻譜儀的靈敏度常以顯示平均噪聲電平來表示Pin = -174dBm + fdB+10logBfdB 整機的噪聲系數(shù)B的

6、3dB中頻帶寬掃 速靈敏度分辨率頻譜分析儀基本概念REF0dBmATTEN10dB當(dāng)VBWRBW時：ST K*SPAN/（RBW）2PEAKLOG 10dB/當(dāng)VBWRBW時：STK*SPAN/（RBW*VBW）同步調(diào)諧濾波器 K>2.5數(shù)字濾波器 K<1CENTER#RES BW300MHzxx MHzSPAN500kHzSWP xx msec#VBWxxMHz掃 速靈敏度分辨率頻譜分析儀基本概念檢波D2D2D2D3D3D3D功率(dB)功率(dB)f2f3f(a二) 階失真2f1-f2（bf1f22f2-f1三階失真動態(tài)范圍信號失真頻譜分析儀基本概念檢波(1kHz)噪聲電平30

7、405060708090二階失真三階失真-70-60-50-40-30-20-10混頻器輸入電平動態(tài)范圍dBc動態(tài)范圍信號失真頻譜分析儀基本概念 檢波PEAKLOG 10 正峰值檢波dB/ROSENFELL檢波取樣檢波負峰值檢波CENTER 300MHzSPAN500 MHzRES BW 1 MHzVBW 1 MHzSWP 50 msec中頻信號頻譜儀經(jīng)包絡(luò)檢波器后有四種REF -40dBmATTEN 10 dB檢波方式動態(tài)范圍信號失真頻譜分析儀基本概念預(yù)選器的特點：預(yù)選器為帶通濾波器，其33ddBB寬為定值，但中心頻率是隨流過自身的電流來改變的，頻率 范圍為22GGHHzz2266.55GG

8、HHzz。它與本振同步調(diào)諧，對帶外和鏡像響應(yīng)有很好的抑制，達到對被測信號的預(yù)選的目的。時 間 門預(yù) 選 器頻譜分析儀基本概念復(fù)合信號觸發(fā)信號時間門實測譜線時 間 門預(yù) 選 器第三章 頻譜測量基礎(chǔ)3.8、頻譜儀使用注意事項3.7、頻譜儀基本操作3.6、頻譜儀誤差分析3.5、頻譜儀基本測量3.4、頻譜儀基本指標3.3、頻譜儀原理實現(xiàn)3.2、頻譜儀基本概念3.1、頻譜儀基礎(chǔ)頻譜分析儀基本原理實現(xiàn)第一第二低通低通濾波器變頻器濾波器變頻器F2IFF1IF第三步進帶寬對數(shù)帶通射頻濾波器變頻器放大器 濾波器 放大器衰減器MXR1F3IFFRFLOGYTFMXR2檢波掃描斜波發(fā)生器F1lo顯示器第一本振YTO

9、器Theory of OperationSpectrum Analyzer Block DiagramRF input attenuatorIF gainIF filterdetectormixerInput signalLog AmpPre-Selector Or Low Pass Filterfilterlocal oscillatorsweep generatorCrystal ReferenceCRT display頻譜儀構(gòu)造框圖說明射頻輸入衰減器中頻濾波器混頻器中頻放大器檢波器混頻器輸入射頻信號Pre-Selector Or Low Pass Filter對數(shù)放大器濾波器本地振蕩器鋸

10、齒波掃平器參考振蕩器屏幕顯示Theory of OperationMixerMIXERinputRFIFf LO- f sigf+ f sig LOf sigLOf sigf LOf LOThe RF mixing processCircuit symbol for an RF mixer頻譜儀工作模式f sSignal RangeLO Rangef LOff- LOf LOf s+s0123(GHz)f sIF filter012456mixer3detectorfs3.66.5input3.6f IFsweep generatorALOf LO0123(GHz)f6345(GHz)LCD

11、display3.66.5通過變頻得到想要的信號fLO-混頻器fLO-finfLO+finLO 掃描fiffinIF filter0 finRangeLOSweep generator00LO Range顯示結(jié)果4213通過變頻得到想要的信號fLO-混頻器fLO-finfLO+finInput signal displayedfLO- fin = fIFfiffin0 finRangeLO00LO Range顯示結(jié)果42fin13進行信號的精確測量-中頻濾波器 IF Bandwidth: also known as resolution bandwidth and RBW Provides s

12、hape of frequency domain signal實際信號顯示信號ff中頻濾波器輸入進行信號的精確測量-中頻濾波器3 dB檢波器Mixer輸入信號中頻濾波器/分辨率帶寬 (RBW)LORBW顯示掃頻3 dB BWTheory of OperationIF FilterIF FILTERInput SpectrumIF Bandwidth (RBW)Display分辨率帶寬RBW對信號和噪聲的影響44頻譜儀分辨率對測量的影響DetectorMixer輸入信號中頻濾波器/分辨率帶寬 (RBW)LORBWDisplaySweep3 dB3 dB BW頻譜儀分辨率對動態(tài)范圍的影響-RBW設(shè)

13、置與動態(tài)范圍噪聲電平改變量 (dB) =10 log(RBW新)/(RBW舊)減小RBW=降低噪聲100 kHz RBW10 dB10 kHz RBW10 dB1 kHz RBW實現(xiàn)各種模式的精確采樣檢波器-檢波器輸入信號幅度largest value in正峰值采樣:bin displayed"bins"負峰值采樣: smallest value inbin displayed平均值采樣: last value in bin displayed檢波方式: Pos Peak,Neg Peak,SamplePos PeakNeg PeakSample采樣點頻譜顯示48檢波方式

14、檢波方式檢波方式小信號的濾波模式-濾波器輸入信號濾波器帶寬(VBW)的設(shè)定對測量結(jié)果影響濾波器為一低通濾波器zl 其主要作用為進行信號檢波，噪聲過濾、平滑，因此將對被測信號帶來失真損傷l 當(dāng)信號夾雜在噪聲中時，通過除噪聲濾波器可有效濾58本振、衰減、放大、掃頻器的相關(guān)信息LO鋸齒波掃描frequencyLCD DISPLAYVCORF 輸入衰減器中頻增益Theory of OperationFront Panel OperationPrimary functions (Frequency, Amplitude, Span)SoftkeysSPECTRUM ANALYZER 9 kHz - 26

15、.5 GHz8563AControl functions (RBW, sweep time, VBW)RF InputNumeric keypadPrimary functions (Frequency, Amplitude, Span)Control functions (RBW, sweep time, VBW)RF InputNumeric keypad第三章 頻譜測量基礎(chǔ)3.8、頻譜儀使用注意事項3.7、頻譜儀基本操作3.6、頻譜儀誤差分析3.5、頻譜儀基本測量3.4、頻譜儀基本指標3.3、頻譜儀原理實現(xiàn)3.2、頻譜儀基本概念3.1、頻譜儀基礎(chǔ)Specifications8563ASP

16、ECTRUM ANALYZER 9 kHz - 26.5 GHzÊ Frequency RangeÊ Accuracy: Frequency & AmplitudeÊ ResolutionÊ SensitivityÊ DistortionÊ Dynamic RangeSpecificationsFrequency RangeLLoowwfrfreeqquueennccieiessfoforrbbaasseebbaannddaannddIFIFMMeeaassuurriningghhaarrmmoonnicicss5500GGH

17、Hzzaannddbbeeyyoonndd!SpecificationsAccuracyAbsolute Amplitude in dBmRelative Amplitude in dBFrequencyRelative FrequencySpecificationsAccuracy: Frequency Readout AccuracyTypical datasheet specification:Spans < 2 MHz:+ (freq. readout x freq. ref. accuracy+ 1% of frequency span+ 15% of resolution b

18、andwidth+ 10 Hz "residual error")FrequencySpecificationsAccuracy: Frequency Readout Accuracy ExampleSingle Marker Example:2 GHz400 kHz span3 kHz RBW(2x109 Hz) x (1.3x10-7 /yr.ref.error) 1% of 400 kHz span15% of 3 kHz RBW 10 Hz residual errorTotal =Calculation:=260 Hz= 4000 Hz=+_450 Hz10 Hz

19、4720 HzSpecificationsAccuracy: Relative Amplitude Accuracyl Display fidelityRelativel Frequency responseAmplitude in dBl RF Input attenuatorl Reference levell Resolution bandwidthl Display scalingSpecificationsAccuracy: Relative Amplitude Accuracy - Display Fidelityl Applies when signals are not pla

20、ced at thesame reference amplitudeRelative Amplitude in dBl Display fidelity includesLog amplifier or linear fidelityDetector linearityDigitizing circuit linearityl Technique for best accuracySpecificationsAccuracy: Relative Amplitude Accuracy - Freq. ResponseSignals in the Same Harmonic Band+1 dB0-

21、 1 dBBAND 1Specification: ± 1 dBSpecificationsAccuracy: Relative Amplitude AccuracyRelativel RF Input attenuatorAmplitude in dBl Reference levell Resolution bandwidthl Display scalingSpecificationsAccuracy: Absolute Amplitude AccuracyAbsolute Amplitude in dBml Calibrator accuracyl Frequency res

22、ponsel Reference level uncertaintySpecificationsResolutionWhat Determines Resolution?Resolution BandwidthResidual FMRBW Type and SelectivityNoise SidebandsSpecificationsResolution: Resolution BandwidthDetectorMixerInput SpectrumIF Filter/Resolution Bandwidth Filter (RBW)LORBWDisplaySweep3 dB3 dB BWD

23、emo- Theory: IF filterOne signal - change RBW to see how display traces out shape of IF filter8447FAmplifierSpectrum Analyzer Setupfc=170 MhzRBW=1 MHz VBW=300 kHzspan=10 MHzSpec AnSignal Generator SetupBandpass filter (center frequency = 170 MHz)f=170 MHz, A=-25 dBmOnOffPower Splitter (used as combi

24、ne)ESG-D4000ASigl GenESG-D4000ASigl GenoutinSpecificationsResolution: Resolution Bandwidth10 kHz RBW3 dB10 kHzDemo- Resolution: RBWTwo equal-amplitude signals spaced 10 kHz apart - change RBW to 10 kHz to see 3 dB 'dip'8447FAmplifierSpectrum Analyzer Setupfc=170 MhzSpec AnRBW=30 kHz VBW=1 kH

25、zspan=100 kHz1 Signal Generator Setupf=170 MHz, A=-25 dBmOnOn2 Signal Generator Setupf=170.01 MHz, A=-25 dBmPower Splitter (used as combiner)ESG-D4000ASigl GenESG-D4000ASigl GenoutinSpecificationsResolution: RBW Type and Selectivity3 dB3 dB BW60 dB60 dB BW60 dB BWSelectivity=3 dB BWSpecificationsRes

26、olution: RBW Type and SelectivityRBW = 1 kHzSelectivity 15:1RBW = 10 kHz3 dBdistortion products7.5 kHz60 dB60 dB BW= 15 kHz10 kHz 10 kHzSpecificationsResolution: Residual FMResidual FM "Smears" the SignalSpecificationsResolution: Noise SidebandsPNoise Sidebands can prevent resolution of un

27、equal signalshase NoiseSpecificationsResolution: RBW Determines Measurement Timept too fastPenalty For Sweeping Too Fast Is An Uncalibrated DisplaySweSpecificationsResolution: Digital Resolution BandwidthsTypical SelectivityAnalogDigital15:15:1ANALOG FILTERDIGITAL FILTERSPAN 3 kHzRES BW 100 HzSpecif

28、icationsSensitivity/DANLDetectorMixerRFInputRES BWFilterLOAASSppeeccttrruummAAnnaalylyzzeerrGGeenneerraatteessaannddAAmmpplilfifieiessNNooisiseeJJuussttLLikikee AAnnyyAAccttiviveeCCirirccuuititSweepSpecificationsSensitivity/DANLsignal level10 dBAttenuation = 20 dBAttenuation = 10 dBSignal-To-Noise R

29、atio Decreases as RF Input Attenuation is IncreasedEEffffeeccttiivvee LLeevveell ooff DDiissppllaayyeedd NNooiissee iiss aa FFuunnccttiioonn ooff RRFF IInnppuutt AAtttteennuuaattiioonnSpecificationsSensitivity/DANL: IF Filter (RBW)100 kHz RBW10 dB10 dB10 kHz RBW1 kHz RBWDecreased BW = Decreased Nois

30、eDDiissppllaayyeedd NNooiissee iiss aa FFuunnccttiioonn ooff IIFF FFiilltteerr BBaannddwwiiddtthhSpecificationsSensitivity/DANL: VBWIIddeennBBWW SSmmooootthheess NNooiissee ffoorr EEaassiieerrttiiffiiccaattiioonn ooff LLooww LLeevveell SSiiggnnaallssSpecificationsSensitivity/DANL2.2 dBSignal Equals

31、NoiseSSeennssiittiivviittyy iiss tthhee SSmmaalleesstt SSiiggnnaall TThhaattCCaann BBee MMeeaassuurreeddSpecificationsSensitivity/DANL+Narrowest Resolution BW+Minimum RF Input Attenuation+SufficientFiltering(BW < .01 Res BW)FFoorr BBeesstt SSeennssiittiivviittyy UUssee:失真對測量動態(tài)范圍的影響-混頻器狀態(tài)與動態(tài)范圍Most

32、 Influential Distortion is the Second and Third Order！< -50< -40 dBc< -50 dBcdBc諧波失真兩音交調(diào)/多階交調(diào)失真對測量動態(tài)范圍的影響-混頻器狀態(tài)與動態(tài)范圍失真產(chǎn)物將隨著輸入信號的變化而變化。33三階信號失真Power in dB兩階產(chǎn)物2f - fff2f - f212211雙音失真23Power in dBSecond Order: 2 dB/dB of Fundamental Third Order:3 dB/dB of Fundamental2f諧波失真3ff混頻器的非線性特性頻譜儀的動態(tài)范圍

33、-設(shè)置與動態(tài)范圍可使用如下方法測量的動態(tài)范圍：u Narrowest Resolution BW（更窄的RBW）u Minimum RF Input Attenuation（降低衰減）u SufficientFiltering足夠的濾波帶寬(BW < .01 Res BW)SpecificationsDistortionMixers Generate DistortionFrequency Translated SignalsResultantSignal To Be MeasuredMixer Generated DistortionSpecificationsDistortionMo

34、st Influential Distortion is the Second and Third Order< -40 dBc< -50 dBc< -50 dBcTwo-Tone IntermodHarmonic DistortionSpecificationsDistortionDistortion Products Increase as a Function of Fundamental's Power33Third-order distortionPower in dBSecond-order distortion2f - fff22f2- f 1121Tw

35、o-Tone Intermod23Power in dBSecond Order: 2 dB/dB of Fundamental Third Order:3 dB/dB of Fundamental2fHarmonic Distortion3ffSpecificationsDistortionRelative Amplitude Distortion Changes with Input Power Level1 dB20 dB1 dB21 dB3 dB2 dB2ff3fSpecificationsDistortionDistortion is a Function of Mixer Leve

36、l0.-20SecondOrder-40-60-80Third Order-100-60-300+30TOIPOWER AT MIXER =INPUT - ATTENUATOR SETTING dBmDISTORTION, dBcSpecificationsDistortionDistortion Test:Is it Internally or Externally Generated?RF INPUTATTENUATORIF GAIN2Watch Signal on Screen:Change Input Attn by 10 dB1¿ No change in amplitud

37、e = distortion is part of input signal (external)¿ Change in amplitude = at least some of the distortion is being generated inside the analyzer (internal)SpecificationsDynamic RangeDynamic Range is defined as theum ratio of two signal levels simultaneously present at the input which can bemeasu

38、red to a specified accuracy. You can imagine connecting two signals to the analyzer input - one which is theum allowable level for the analyzer's input range and the other which is much smaller. The smaller one is reduced in amplitude until it is no longer detectable by the analyzer. When the sm

39、aller signal is just measurable, the ratio of the two signal levels (in dB) defines the dynamic range of the analyzer.What effects might make it undetectable? All the things we've just discussed. Such things as residual responses of the analyzer, harmonic distortion of the large signal (due to a

40、nalyzer imperfections), and the internal noise of the analyzer.These will all be large enough to cover up the smaller signal as we decrease its amplitude. The dynamic range of the instrument determines the amplitude range over which we can reliably make measurements.DDyynnaammiiccRRaannggeeSpecificationsDynamic RangeSignal-to-Noise Ratio Can Be Graphed0.-20-40-60-80-100-60-300+30POWER AT MIXER =I