Network Analyzer Basics-EE142 Fall 07

1 Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Network Analyzer Basics- EE142 Fall 07 Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 RFIncidentReflectedTransmittedLightwaveD UTL ightwave Analogy to RF EnergyNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Verify specifications of building blocks for more complex RF systems Create models for simulation Check our simulation models against a real circuit Ensure good match when absorbing power ( , an antenna)Why Do We Need to Test Components?KPWRFM 97 Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS1424.

2 Time-domain characterization MagTime5. Vector-error correctionErrorMeasuredActual2. Complex impedance needed to design matching circuits3. Complex values needed for device modeling 1. Complete characterization of linear networks High-frequency transistor model CollectorBaseEmitterS21S12S11S22 The Need for Both Magnitude and PhaseNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Low frequencies wavelengths >> wire length current (I) travels down wires easily for efficient power transmission measured voltage and current not dependent on position along wireHigh frequencies wavelength or << length of transmission medium need transmission lines for efficient power transmission matching to characteristic impedance (Zo)

3 Is very important for low reflection and maximum power transfer measured envelope voltage dependent on position along lineI+-Transmission Line BasicsNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Transmission line Zo Zodetermines relationship between voltage and current waves Zois a function of physical dimensions and r Zois usually a real impedance ( 50 or 75 ohms)characteristic impedancefor coaxial airlines (ohms)10203040506070 80 90 values50 ohm standardattenuation is lowest at 77 ohmspower handling capacity peaks at 30 ohmsMicrostriphwCoplanar w1w2 rWaveguideTwisted-pairCoaxial bahNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 RSRLFor complex impedances, maximum power transfer occurs when ZL= ZS*(conjugate match)Maximum power is transferred whenRL= RSRL/ 1 2 3 4 5 6 7 8 9 10 Load Power (normalized)

4 RsRL+jX-jXPower Transfer EfficiencyNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission lineZs = ZoZoVrefl = 0! (all the incident poweris absorbed in the load)VincZo = characteristic impedance of transmission lineTransmission Line Terminated with ZoNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142Zs = ZoVreflVincFor reflection, a transmission line terminated in a short or open reflects all power back to sourceIn-phase (0o) for open, out-of-phase (180o)

5 For shortTransmission Line Terminated with Short, OpenNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 VreflStanding wave pattern does not go to zero as with short or openZs = ZoZL= 25 VincTransmission Line Terminated with 25 Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 TransmittedIncidentTRANSMISSIONGain / LossS-ParametersS21, S12 GroupDelayTransmissionCoefficientInserti on PhaseReflectedIncidentREFLECTIONSWRS-Par ametersS11, S22 ReflectionCoefficientImpedance, Admittance R+jX, G+jB ReturnLoss , , IncidentReflectedTransmittedRBAAR=BR=Hig h-Frequency Device CharacterizationNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 dBNo reflection(ZL= Zo) RLVSWR01 Full reflection(ZL= open, short)0 dB1 =ZL ZOZL+OZReflection Coefficient=VreflectedVincident= = Return loss= -20 log( ),Voltage Standing Wave RatioVSWR= EmaxEmin=1 + 1 - EmaxEminReflection ParametersNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 VTransmittedVIncidentTransmission Coefficient = =VTransmittedVIncident= DUTGain (dB)

6 = 20 Log VTrans VInc = 20 log Insertion Loss (dB) = - 20 Log VTrans VInc = - 20 log Transmission ParametersNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Linear behavior: input and output frequencies are the same (no additional frequencies created) output frequency only undergoes magnitude and phase changeFrequencyf1 TimeSin 360o* f * tFrequencyAphase shift = to* 360o* f1fDUTTimeAtoA * Sin 360o* f (t - to)InputOutputTimeNonlinear behavior: output frequency may undergo frequency shift ( with mixers) additional frequencies created (harmonics, intermodulation)Frequencyf1 Linear Versus Nonlinear BehaviorNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Constant amplitudeover bandwidth of interestMagnitudePhaseFrequencyFrequency Linear phaseover bandwidth of interestCriteria for Distortionless TransmissionLinear NetworksNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142F(t)

7 = sin wt+ 1/3 sin 3wt+ 1/5 sin 5wtTimeLinear NetworkFrequencyFrequencyFrequencyMagnit udeTimeMagnitude Variation with FrequencyNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 FrequencyMagnitudeLinear NetworkFrequencyFrequencyTime0-180-360 TimeF(t) = sin wt+ 1 /3 sin 3wt+ 1 /5 sin 5wtPhase Variation with FrequencyNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Use electrical delay to remove linear portion of phase responseLinear electrical length added+yieldsFrequency(Electrical delay function)FrequencyRF filter responseDeviation from linear phasePhase 1 /DivoPhase 45 /DivoFrequencyLow resolutionHigh resolutionDeviation from Linear PhaseNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142in radiansin radians/secin degreesf in Hertz ( = 2 f) Group Delay (t )

8 G= d d = 1360od d f*FrequencyGroup delay rippleAverage delaytotgPhase Frequency group-delay ripple indicates phase distortion average delay indicates electrical length of DUT aperture of measurement is very importantGroup DelayNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Same p-p phase ripple can result in different group delayPhasePhaseGroup DelayGroup Delay d d d d ffffWhy Measure Group Delay? Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 Using parameters (H, Y, Z, S) to characterize devices.

9 Gives linear behavioral model of our device measure parameters ( voltage and current) versus frequency under various source and load conditions ( short and open circuits) compute device parameters from measured data predict circuit performance under any source and load conditionsH-parametersV1= h11I1+ h12V2I2= h21I1+ h22V2Y-parametersI1= y11V1+ y12V2I2= y21V1+ y22V2Z-parametersV1= z11I1+ z12I2V2= z21I1+ z22I2h11= V1I1V2=0h12= V1V2I1=0(requires short circuit)(requires open circuit)Characterizing Unknown DevicesNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142 relatively easy to obtainat high frequencies measure voltage traveling waves with a vector Network Analyzer don't need shorts/opens which can cause active devices to oscillate or self-destruct relate to familiarmeasurements (gain, loss, reflection coefficient.)

10 Can cascadeS-parameters of multiple devices to predict system performance can computeH, Y, or Z parameters from S-parameters if desired can easily import and use S-parameter files in our electronic-simulationtoolsIncidentTransm ittedS21S11 ReflectedS22 ReflectedTransmittedIncidentb1a1b2a2S12 DUTb1= S11a1+S12a2b2=S21a1+S22a2 Port 1 Port 2 Why Use S-Parameters? Network Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142S11=ReflectedIncident=b1a1a2=0S21 =TransmittedIncident=b2a1a2=0S22=Reflect edIncident=b2a2a1=0S12=TransmittedIncide nt=b1a2a1=0 IncidentTransmittedS21S11 Reflectedb1a1b2Z0 Loada2=0 DUTF orwardIncidentTransmittedS12S22 Reflectedb2a2ba1=0 DUTZ0 LoadReverse1 Measuring S-ParametersNetwork Analyzer BasicsJoel Dunsmore Copyright 2007 EECS142S11 = forward reflection coefficient (input match)S22 = reverse reflection coefficient (output match)S21 = forward transmission coefficient (gain or loss)