Network Analyzer Basics

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2 Network Analysis is NOT. Router Bridge Repeater Hub Your IEEE X.25 ISDN switched-packet data stream is running at 147 MBPS with -9 a BER of X 10...

3 What Types of Devices are Tested? Integration High Low Duplexers Diplexers Filters Couplers Bridges Splitters, dividers Combiners Isolators Circulators Attenuators Adapters Opens, shorts, loads Delay lines Cables Transmission lines Waveguide Resonators Dielectrics R, L, C's Antennas Switches Multiplexers Mixers Samplers Multipliers Diodes RFICs MMICs T/R modules Transceivers Receivers Tuners Converters VCAs Amplifiers VCOs VTFs Oscillators Modulators VCAtten s Transistors Passive Device type Active

4 Device Test Measurement Model Complex Response tool Simpl e Ded. Testers VSA SA VNA TG/SA SNA NF Mtr. Imped. An. Param. An. Power Mtr. Det/Scope Harm. Dist. LO stability Image Rej. I-V LCR/Z Gain/Flat. Compr'n Phase/GD AM-PM Isolation Rtn Ls/VSWR Impedance S-parameters Absol. Power Gain/Flatness NF NF RFIC test Intermodulation Distortion Measurement plane DC CW Swept Swept Noise 2-tone Multi- Complex Pulsed- Protocol freq power tone modulation RF Simple Complex Stimulus type BER EVM ACP Regrowth Constell. Eye Full call sequence Pulsed S-parm. Pulse profiling

5 Lightwave Analogy to RF Energy Incident Transmitted Reflected Lightwave DUT RF

6 Why Do We Need to Test Components? Verify specifications of building blocks for more complex RF systems Ensure distortionless transmission of communications signals linear: constant amplitude, linear phase / constant group delay nonlinear: harmonics, intermodulation, compression, AMto-PM conversion Ensure good match when absorbing power (e.g., an antenna) KPWR FM 97

7 The Need for Both Magnitude and Phase 1. Complete characterization of linear networks 2. Complex impedance needed to design matching circuits S 21 S 11 S 22 S Time-domain characterization Mag 3. Complex values needed for device modeling Base High-frequency transistor model Emitter Collector Time 5. Vector-error correction Error Measured Actual

8 Agenda What measurements do we make? Transmission-line basics Reflection and transmission parameters S-parameter definition Network analyzer hardware Signal separation devices Detection types Dynamic range T/R versus S-parameter test sets Error models and calibration Types of measurement error One- and two-port models Error-correction choices Basic uncertainty calculations Example measurements Appendix

9 Transmission Line Basics + - I Low frequencies wavelengths >> wire length current (I) travels down wires easily for efficient power transmission measured voltage and current not dependent on position along wire High frequencies wavelength or << length of transmission medium need transmission lines for efficient power transmission matching to characteristic impedance (Zo) is very important for low reflection and maximum power transfer measured envelope voltage dependent on

10 Transmission line Zo Zo determines relationship between voltage and current waves Zo is a function of physical dimensions and ε r Zo is usually a real impedance (e.g. 50 or 75 ohms) Twisted-pair Waveguide attenuation is lowest at 77 ohms a b Coaxial w2 Coplanar w1 εr h w Microstrip h normalized values ohm standard power handling capacity peaks at 30 ohms characteristic impedance for coaxial airlines (ohms)

11 Power Transfer Efficiency RS Load Power (normalized) RL / RS RL For complex impedances, maximum power transfer occurs when ZL = ZS* (conjugate match) Rs +jx -jx RL Maximum power is transferred when RL = RS

12 Transmission Line Terminated with Zo Zs = Zo Zo = characteristic impedance of transmission line Zo V inc Vrefl = 0! (all the incident power is absorbed in the load) For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line

13 Transmission Line Terminated with Short, Open Zs = Zo V inc Vrefl In-phase (0 o ) for open, out-of-phase (180 o ) for short For reflection, a transmission line terminated in a short or open reflects all power back to source

14 Transmission Line Terminated with 25 Ω Zs = Zo ZL = 25 Ω V inc Vrefl Standing wave pattern does not go to zero as with short or open

15 High-Frequency Device Characterization Incident R Reflected A REFLECTION Transmitted B TRANSMISSION Reflected Incident = A R Transmitted Incident = B R SWR S-Parameters S 11, S 22 Reflection Coefficient Γ, ρ Return Loss Impedance, Admittance R+jX, G+jB Gain / Loss S-Parameters S 21, S 12 Transmission Coefficient Τ,τ Insertion Phase Group Delay

16 Reflection Parameters Reflection Coefficient Γ Return loss = -20 log(ρ), = V reflected V incident = ρ Φ ρ = Γ = Z L Z O Z L + ZO Emax Emin Voltage Standing Wave Ratio VSWR = Emax Emin = 1 + ρ 1 - ρ No reflection (ZL = Zo) Full reflection (ZL = open, short) 0 ρ 1 db RL 0 db 1 VSWR

17 Smith Chart Review. +jx Polar plane 90 o R o o -jx Rectilinear impedance plane Smith Chart maps rectilinear impedance plane onto polar plane 0 Z = 0 L Γ Z = Zo L Γ = 0-90 o (short) Z = L = 1 ±180 O Smith chart Constant X Γ Constant R = 1 0 O (open)

18 Transmission Parameters V Incident DUT V Transmitted Transmission Coefficient = Τ = V Transmitted V Incident = τ φ V Trans Insertion Loss (db) = - 20 Log V Inc = - 20 log τ V Trans Gain (db) = 20 Log V Inc = 20 log τ

19 Linear Versus Nonlinear Behavior Sin 360 o * f * t A t o A A * Sin 360 o * f (t - t o ) Time phase shift = to * 360 o * f Linear behavior: input and output frequencies are the same (no additional frequencies created) output frequency only undergoes magnitude and phase change Time f 1 Frequency Input DUT Output f 1 Frequency f 1 Nonlinear behavior: output frequency may undergo frequency shift (e.g. with mixers) additional frequencies created (harmonics, Frequency intermodulation) Time

20 Criteria for Distortionless Transmission Linear Networks Constant amplitude over bandwidth of interest Linear phase over bandwidth of interest Magnitude Phase Frequency Frequency

21 Magnitude Variation with Frequency F(t) = sin wt + 1/3 sin 3wt + 1/5 sin 5wt Time Time Linear Network Magnitude Frequency Frequency Frequency

22 Phase Variation with Frequency F(t) = sin wt + 1 /3 sin 3wt + 1 /5 sin 5wt Linear Network Time Time Magnitude Frequency Frequency Frequency -360

23 Deviation from Linear Phase Use electrical delay to remove linear portion of phase response o Phase 45 /Div RF filter response Linear electrical length added (Electrical delay function) + yields Deviation from linear phase o Phase 1 /Div Frequency Frequency Frequency Low resolution High resolution

24 Group Delay Phaseφ Δφ Frequency Δω ω t g t o Group delay ripple Average delay Group Delay (t ) g = d φ d ω = 1 φ ω φ in radians in radians/sec in degrees * d φ 360 o d f f in Hertz (ω = 2 π f) Frequency group-delay ripple indicates phase distortion average delay indicates electrical length of DUT aperture of measurement is very important

25 Why Measure Group Delay? Phase Phase d φ d ω f d φ d ω f Group Delay Group Delay f Same p-p phase ripple can result in different group delay f

26 Characterizing Unknown Devices Using parameters (H, Y, Z, S) to characterize devices: gives linear behavioral model of our device measure parameters (e.g. voltage and current) versus frequency under various source and load conditions (e.g. short and open circuits) compute device parameters from measured data predict H-parameters circuit performance Y-parameters under any source Z-parameters and load conditions V1 = h11i1 + h12v2 I1 = y11v1 + y12v2 V1 = z11i1 + z12i2 I2 = h21i1 + h22v2 I2 = y21v1 + y22v2 V2 = z21i1 + z22i2 h11 = V1 I1 V2=0 h12 = V1 V2 I1=0 (requires short circuit) (requires open circuit)

27 Why Use S-Parameters? relatively easy to obtain at 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 familiar measurements (gain, loss, reflection coefficient...) can cascade S-parameters of multiple devices to predict system performance can compute H, Y, or Z parameters from S-parameters if desired can easily import and Incident S21 use S-parameter Transmitted files in our electronicsimulation tools S11 a1 b2 b1 Reflected Transmitted DUT Port 1 Port 2 S12 b1 =S11a 1 + S 12 a2 b2 = S21 a 1 + S22 a2 S22 Reflected a2 Incident

28 Measuring S-Parameters Incident S 21 Transmitted Forward b 1 a 1 b 2 Z 0 S 11 Reflected DUT a 2 = 0 Load S 11 = S 21 Reflected Incident = Transmitted Incident = b 1 a 1 a 2 = 0 = b 2 a 1 a 2 = 0 S 22 = S 12 Reflected Incident = Transmitted Incident = b 2 a 2 a 1 = 0 = b 1 a 2 a 1 = 0 Z 0 Load a 1 = 0 b 1 DUT Transmitted S 12 S 22 Reflected Incident b 2 a 2 Reverse

29 Equating S-Parameters with Common Measurement Terms S11 = forward reflection coefficient (input match) S22 = reverse reflection coefficient (output match) S21 = forward transmission coefficient (gain or loss) S12 = reverse transmission coefficient (isolation) Remember, S-parameters are inherently complex, linear quantities -- however, we often express them in a log-magnitude format

30 Criteria for Distortionless Transmission Nonlinear Networks Saturation, crossover, intermodulation, and other nonlinear effects can cause signal distortion Effect on system depends on amount and type of distortion and system architecture Time Time Frequency Frequency

31 SPECTRUM ANALYZER 9 khz GHz Measuring Nonlinear Behavior Most common measurements: using a network analyzer and power sweeps gain compression AM to PM conversion using a spectrum analyzer + source(s) harmonics, particularly second and third intermodulation products resulting from two or more RF carriers LPF DUT 8563A RL 0 dbm ATTEN 10 db 10 db / DIV LPF CENTER MHz SPAN khz RB 30 Hz VB 30 Hz ST 20 sec

32 . What is the Difference Between Network and Spectrum Analyzers? 8563A SPECTRUM ANALYZER 9 khz GHz Amplitude Ratio Measures known signal Amplitude Measures unknown signals Frequency Network analyzers: measure components, devices, circuits, sub-assemblies contain source and receiver display ratioed amplitude and phase (frequency or power sweeps) Network offer Analyzer advanced Basics error correction Frequency Spectrum analyzers: measure signal amplitude characteristics carrier level, sidebands, harmonics...) can demodulate (& measure) complex signals are receivers only (single channel) can be used for scalar component test (no phase) with tracking gen or ext

33 Agenda What measurements do we make? Network analyzer hardware Error models and calibration Example measurements Appendix

34 Generalized Network Analyzer Block Diagram Incident DUT Transmitted SOURCE Reflected SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY

35 Source Supplies stimulus for system Swept frequency or power Traditionally NAs used separate source Most Agilent analyzers sold today have integrated, synthesized sources

36 Signal Separation SOURCE Incident Reflected DUT Transmitted SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR measure incident signal for reference separate incident and reflected signals PROCESSOR / DISPLAY splitter bridge directional coupler Detector Test Port

37 Directivity Directivity is a measure of how well a coupler can separate signals moving in opposite directions (undesired leakage signal) (desired reflected signal) Test port Directional Coupler

38 Interaction of Directivity with the DUT (Without Error Correction) 0 DUT RL = 40 db Data Max Return Loss 30 Device Directivity Add in-phase 60 Frequency Directivity Device Data Min Add out-of-phase (cancellation) Directivity Device Data = Vector Sum

39 Detector Types Diode Scalar broadband (no phase information) SOURCE INCIDENT (R) Incident Reflected REFLECTED (A) DUT SIGNAL SEPARATION TRANSMITTED (B) RECEIVER / DETECTOR Transmitted RF DC AC PROCESSOR / DISPLAY Tuned Receiver RF IF = F LO ± F RF ADC / DSP Vector (magnitude and phase) IF Filter LO

40 Broadband Diode Detection Easy to make broadband Inexpensive compared to tuned receiver Good for measuring frequency-translating devices Improve dynamic range by increasing power Medium sensitivity / dynamic range 10 MHz 26.5 GHz

41 Narrowband Detection - Tuned Receiver ADC / DSP Best sensitivity / dynamic range Provides harmonic / spurious signal rejection Improve dynamic range by increasing power, decreasing IF bandwidth, or averaging Trade off noise floor and measurement speed 10 MHz 26.5 GHz

42 Comparison of Receiver Techniques 0 db Broadband (diode) detection 0 db Narrowband (tuned-receiver) detection -50 db -50 db -100 db -100 db -60 dbm Sensitivity < -100 dbm Sensitivity higher noise floor false responses high dynamic range harmonic immunity Dynamic range = maximum receiver power - receiver noise floor

43 Dynamic Range and Accuracy 100 Error Due to Interfering Signal 10 - Error (db, deg) magn error phase error Dynamic range is very important for measurement accuracy! Interfering signal (db)

44 T/R Versus S-Parameter Test Sets Transmission/Reflection Test Set S-Parameter Test Set Source Source Transfer switch R R A B A B Port 1 Port 2 Port 1 Port 2 Fwd DUT Fwd DUT Rev RF always comes out port 1 port 2 is always receiver response, one-port cal available RF comes out port 1 or port 2 forward and reverse measurements two-port calibration possible

45 Hld Cor PRm Hld Cor PRm 1 CH2 START MHz MHz START CH1 Duplexer Test - Tx-Ant and Ant-Rx S CH2 S 12 log MAG REF 0 db 10 db/ db 0 REF db/ 10 MAG log 21 CH1 1 STOP MHz MHz STOP MHz MHz PASS PASS 1_ db db _ 2 HP-IB STATUS Processor / Display Incident DUT Transmitted 50 MH-20GHz NETWORK ANYZER SOURCE Reflected ACTIVE CHANNEL RESPONSE ENTRY SIGNAL SEPARATION STIMULUS INSTRUMENT STATE R CHANNEL INCIDENT (R) REFLECTED (A) TRANSMITTED (B) T R L S RECEIVER / DETECTOR PORT 1 PORT 2 PROCESSOR / DISPLAY CH2 START MHz STOP MHz CH1 START MHz STOP MHz Hld PASS 2 markers limit lines pass/fail indicators linear/log formats grid/polar/smith charts Cor PRm 1 Hld 1 Cor Duplexer Test - Tx-Ant Ant-Rx and PRm S 12 log MAG REF 0 db 10 db/ CH2 db 0 REF db/ 10 MAG log 21 S CH MHz PASS MHz db _ db _

46 Internal Measurement Automation Simple: recall states More powerful: Test sequencing available on 8753/ 8720 families keystroke recording some advanced functions IBASIC available on 8712 family sophisticated programs custom user interfaces ABCDEFGHIJKLMNOPQRSTUVWXYZ / * = < > ( ) & "" ",. /? ; : ' [ ] 1 TO *WAI" 3 OFF;*WAI" 4 SSTOP" 5 CSPAN" HZ;*WAI" 7 OFF;:INIT1;*WAI" 8 ONCE" 9 ON" 10 BWID" 11 ON; *WAI" 12 'XFR:POW:RAT 1,0';DET NBAN; *WAI" 13 OFF;:INIT1;*WAI" 14 ONCE" 15 ON;*WAI" 16 END

47 Agilent s Series of HF Vector Analyzers Microwave 8720ET/ES series 13.5, 20, 40 GHz economical fast, small, integrated test mixers, high-power amps RF 8712ET/ES series 1.3, 3 GHz low cost narrowband and broadband detection IBASIC / LAN 8510C series 110 GHz in coax highest accuracy modular, flexible pulse systems Tx/Rx module test 8753ET/ES series 3, 6 GHz highest RF accuracy flexible hardware more features Offset and harmonic RF sweeps

48 Agilent s LF/RF Vector Analyzers Combination NA / SA 4395A/4396B 500 MHz (4395A), 1.8 GHz (4396B) impedance-measuring option fast, FFT-based spectrum analysis time-gated spectrum-analyzer option IBASIC standard test fixtures LF E5100A/B 180, 300 MHz economical fast, small target markets: crystals, resonators, filters equivalent-circuit models evaporation-monitor-function option

49 SPECTRUM ANALYZER 9 khz GHz Spectrum Analyzer / Tracking Generator RF in DUT LO IF 8563A Spectrum analyzer TG out f = IF Tracking generator DUT Key differences from network analyzer: one channel -- no ratioed or phase measurements More expensive than scalar NA (but better dynamic range) Only error correction available is normalization (and possibly open-short averaging) Poorer accuracy Small incremental cost if SA is required for other measurements

50 Agenda What measurements do we make? Network analyzer hardware Error models and calibration Example measurements Appendix Why do we even need error-correction and calibration? It is impossible to make perfect hardware It would be extremely expensive to make hardware good enough to eliminate the need for error correction

51 Calibration Topics What measurements do we make? Network analyzer hardware Error models and calibration measurement errors what is vector error correction? calibration types accuracy examples calibration considerations Example measurements Appendix

52 Measurement Error Modeling CAL RE-CAL Systematic errors due to imperfections in the analyzer and test setup assumed to be time invariant (predictable) Random errors vary with time in random fashion (unpredictable) main contributors: instrument noise, switch and connector repeatability Drift errors due to system performance changing after a calibration has been done primarily caused by temperature variation Measured Data Errors: SYSTEMATI C RANDO M Unknown Device DRIFT

53 Systematic Measurement Errors R Directivity A Crosstalk B DUT Frequency response reflection tracking (A/R) transmission tracking (B/R) Source Mismatch Load Mismatch Six forward and six reverse error terms yields 12 error terms for twoport devices

54 Types of Error Correction response (normalization) simple to perform only corrects for tracking errors stores reference trace in memory, thru then does data divided by memory vector requires more standards requires an analyzer that can measure phase accounts for all major sources of systematic error SHORT S 11a OPEN thru S 11m LOAD

55 What is Vector-Error Correction? Process of characterizing systematic error terms measure known standards remove effects from subsequent measurements 1-port calibration (reflection measurements) only 3 systematic error terms measured directivity, source match, and reflection tracking Full 2-port calibration (reflection and transmission measurements) 12 systematic error terms measured usually requires 12 measurements on four known standards (SOLT) Standards defined in cal kit definition file network analyzer contains standard cal kit definitions CAL KIT DEFINITION MUST MATCH ACTUAL CAL KIT USED! User-built standards must be characterized and entered into user cal kit

56 Reflection: One-Port Model RF in Ideal RF in Error Adapter 1 E D = Directivity S11 A E D E S S11A E RT E S = Reflection tracking = Source Match S11 M S11 M S11 M = Measured E RT S11 A = Actual To solve for error terms, we measure 3 standards to generate 3 equations and 3 unknowns S11M = ED + Assumes good termination at port two if testing two-port devices If using port 2 of NA and DUT reverse isolation is low (e.g., filter passband): assumption of good termination is not valid two-port error correction yields better results ERT S11A 1 - ES S11A

57 Before and After One-Port Calibration Return Loss (db) data before 1-port calibration VSWR 60 data after 1-port calibration MHz

58 RT S E RT E E D E S E L E L E TT S m E X S m E X m E S E RT E S S m E D RT S L E L E TT E m E X E m E X S E S RT S L E TT E E E X S m E X E m S E TT m D E TT S m E D E TT S m E X RT S E RT E E D E S E L E L E TT S m E X S m E X m E S RT E RT E D E S E L E TT S m E X S m E X E m S a 1 b 1 Two-Port Error Correction Forward model Port 1 EX Port 2 S 21 E b A TT 2 E S E D S 11 S 22 a A A 2 E L E RT S 12 A Reverse model Port 1 Port 2 E RT' S21 a A 1 E L' S 11 S 22 E ES' D' A A b 1 E TT' S 12 A E X' b 2 a 2 E D E S E RT E D' E S' ERT' = fwd directivity = fwd source match = fwd reflection tracking = rev directivity = rev source match = rev reflection tracking E L E TT E X E L' ETT' E X' = fwd load match = fwd transmission tracking = fwd isolation = rev load match = rev transmission tracking = rev isolation a 22 S )( m ( D E S ') ( )( ' ' ' ) ' ' S 12a = = E RT ( 1 + S TT ' E ' m E D )( ') ' ( )( 1 ' E S 11 D m E S ' E RT ( 1 )( + 22 D E m S ' ' E TT ) m '( D )( E S ' E TT ' ' ) ) Each actual S-parameter is a function of all four measured S-parameters Analyzer must make forward and reverse sweep to update any one S-parameter Luckily, you don't need to know these equations to use network analyzers!!! m D ( 1 )( E S a 21 = S X E m S m D' ( 1 )( E S a 11 = S D E m S 1 + ( )( 11 E RT ( )( ( ' )) m X E S E L E S E S ' RT S L ' ' E E E ') ' ( )( E L E TT S m E X ' RT S L E ' E + ( E )( ( ' )) 1 ' TT ' ' E ') ' ( )( TT ' ' E ') ( )( ' ' ) ' ) ' ) '

59 Crosstalk: Signal Leakage Between Test Ports During Transmission Can be a problem with: high-isolation devices (e.g., switch in open position) high-dynamic range devices (some filter stopbands) Isolation calibration adds noise to error model (measuring near noise floor of system) only perform if really needed (use averaging if necessary) if crosstalk is independent of DUT match, use two terminations if dependent on DUT match, use DUT with termination on output LOAD DUT DUT LOAD DUT

60 Convenient Generally not accurate No errors removed Errors and Calibration Standards UNCORRECTED RESPONSE FULL 2-PORT DUT thru DUT Easy to perform Use when highest accuracy is not required Removes frequency response error ENHANCED-RESPONSE Combines response and 1-port Corrects source match for transmission measurements SHORT OPEN LOAD DUT For reflection measurements Need good termination for high accuracy with twoport devices Removes these errors: Directivity Source match Reflection tracking 1-PORT SHORT OPEN LOAD Highest accuracy Removes these errors: Directivity Source, load match Reflection tracking Transmission tracking Crosstalk thru DUT SHORT OPEN LOAD

61 Calibration Summary Reflection Reflection tracking Test Set (cal type) T/R (one-port) S-parameter (two-port) SHORT OPEN Directivity LOAD Source match Load match * error can be corrected error cannot be corrected enhanced response cal corrects for source match during transmission measurements Transmission Transmission Tracking Crosstalk Source match Load match * ( ) Test Set (cal type) T/R S-parameter (response, isolation) (two-port)

62 Reflection Example Using a One-Port Cal Directivity: 40 db (.010) Load match: 18 db (.126) DUT 16 db RL (.158) 1 db loss (.891) Remember: convert all db values to linear for uncertainty calculations! -db ( ) 20 ρ or loss (linear) = (.891)(.126)(.891) =.100 Measurement uncertainty: -20 * log ( ) = 11.4 db (-4.6dB) -20 * log ( ) = 26.4 db (+10.4 db)

63 Using a One-Port Cal + Attenuator Directivity: 40 db (.010).158 Load match: 18 db (.126) 10 db attenuator (.316) SWR = 1.05 (.024) DUT 16 db RL (.158) 1 db loss (.891) Measurement uncertainty: -20 * log ( ) = 14.1 db (-1.9 db) -20 * log ( ) = 18.5 db (+2.5 db) (.891)(.316)(.126)(.316)(.891) =.010 (.891)(.024)(.891) =.019 Worst-case error = =.039 Low-loss bi-directional devices generally require two-port calibration for low measurement uncertainty

64 Transmission Example Using Response Cal RL = 14 db (.200) RL = 18 db (.126) Thru calibration (normalization) builds error into measurement due to source and load match interaction Calibration Uncertainty = (1 ± ρ S ρ L ) = (1 ± (.200)(.126) = ± 0.22 db

65 Filter Measurement with Response Cal Source match = 14 db (.200) DUT 1 db loss (.891) 16 db RL (.158) Load match = 18 db (.126) 1 (.126)(.158) =.020 (.126)(.891)(.200)(.891) =.020 Total measurement uncertainty: = db = db (.158)(.200) =.032 Measurement uncertainty = 1 ± ( ) = 1 ±.072 = db db

66 Measuring Amplifiers with a Response Cal Source match = 14 db (.200) DUT 16 db RL (.158) Load match = 18 db (.126) 1 (.126)(.158) =.020 (.158)(.200) =.032 Total measurement uncertainty: = db = db Measurement uncertainty = 1 ± ( ) = 1 ±.052 = db db

67 Source match = 35 db (.0178) Filter Measurements using the Enhanced Response Calibration Effective source match = 35 db! DUT 1 db loss (.891) 16 db RL (.158) Load match = 18 db (.126) Calibration Uncertainty = (1 ± ρ S ρ L ) = (1 ± (.0178)(.126) = ±.02 db 1 (.126)(.158) =.020 (.126)(.891)(.0178)(.891) =.0018 (.158)(.0178) =.0028 Measurement uncertainty = 1 ± ( ) = 1 ±.0246 = db db Total measurement uncertainty: = ± 0.24 db

68 Source match = 35 db (.0178) Using the Enhanced Response Calibration Plus an Attenuator 10 db attenuator (.316) SWR = 1.05 (.024 linear or 32.4 db) Analyzer load match =18 db (.126) DUT 1 db loss (.891) 16 db RL (.158) Effective load match = (.316)(.316)(.126) =.0366 (28.7dB) 1 (.0366)(.158) =.006 (.0366)(.891)(.0178)(.891) =.0005 (.158)(.0178) =.0028 Calibration Uncertainty = (1 ± ρ S ρ L ) = (1 ± (.0178)(.0366) = ±.01 db Measurement uncertainty = 1 ± ( ) = 1 ±.0093 = ± 0.08 db Total measurement uncertainty: = ± 0.09 db

69 Calculating Measurement Uncertainty After a Two-Port Calibration Corrected error terms: (8753ES GHz Type-N) Directivity = 47 db Source match = 36 db Load match = 47 db Refl. tracking =.019 db Trans. tracking =.026 db Isolation = 100 db Transmission uncertainty DUT 1 db loss (.891) 16 db RL (.158) Reflection uncertainty = ± (.. *.. *.. *. ) 2 a D a S a a L a RT m S S E S E S S E S E 1 = ± ( ( )) = ±.0088 = 16 db db, db (worst-case) = ± ( /.. *.. *. *.. *.. ) a a I a a S a a S L a L TT m = ±.0056 = 1 db ±0.05 db (worst-case) S S E S S E S S E E S E E 1 = ± ( / ( )) S

70 Response versus Two-Port Calibration Measuring filter insertion loss CH1 S21&M log MAG 1 db/ REF 0 db CH2 MEM log MAG 1 db/ REF 0 db Cor After two-port calibration After response calibration Cor Uncorrected x2 1 2 START MHz STOP MHz

71 ECal: Electronic Calibration (85060/90 series) Variety of modules cover 30 khz to 26.5 GHz Six connector types available (50 Ω and 75 Ω) Single-connection reduces calibration time makes calibrations easy to perform minimizes wear on cables and standards eliminates operator errors Highly repeatable temperaturecompensated terminations provide excellent accuracy 85093A Electronic Calibration Module 30 khz - 6 GHz Microwave modules use a transmission line shunted by PIN-diode switches in various combinations

72 Adapter Considerations reflection from adapter leakage signal Coupler directivity = 40 db desired signal ρ measured = Directivity + adapter + ρ ρ DUT Adapter DUT Termination DUT has SMA (f) connectors Worst-case System Directivity Adapting from APC-7 to SMA (m) APC-7 calibration done here 28 db APC-7 to SMA (m) SWR: db APC-7 to N (f) + N (m) to SMA (m) SWR:1.05 SWR: db APC-7 to N (m) + N (f) to SMA (f) + SMA (m) to (m) SWR:1.05 SWR:1.25 SWR:1.15

73 Calibrating Non-Insertable Devices When doing a through cal, normally test ports mate directly cables can be connected directly without an adapter result is a zero-length through What is an insertable device? has same type of connector, but different sex on each port has same type of sexless connector on each port (e.g. APC-7) What is a non-insertable device? one that cannot be inserted in place of a zerolength through has same connectors on each port (type and sex) has different type of connector on each port (e.g., waveguide on one port, coaxial on the other) What calibration choices do I have for non- DUT

74 Swap Equal Adapters Method Port 1 DUT Port 2 Adapter Port 1 A Port 2 Accuracy depends on how well the adapters are matched - loss, electrical length, match and impedance should all be equal 1. Transmission cal using adapter A. Port 1 Adapter Port 2 B 2. Reflection cal using adapter B. Port 1 DUT Adapter Port 2 B 3. Measure DUT using adapter B.

75 Adapter Removal Calibration Calibration is very accurate and traceable In firmware of 8753, 8720 and 8510 series Also accomplished with ECal modules (85060/90) Uses adapter with same connectors as DUT Must specify electrical length of adapter to within 1/4 wavelength of highest frequency (to avoid phase ambiguity) Port 1 DUT Port 2 Cal Port 1 Adapter Port 2 Adapter B Cal Set 1 Port 1 Cal Adapter Adapter B Port 2 Cal Set 2 [CAL] [MORE] [MODIFY CAL SET] [ADAPTER REMOVAL] 1. Perform 2-port cal with adapter on port 2. Save in cal set Perform 2-port cal with adapter on port 1. Save in cal set Use ADAPTER REMOVAL to generate new cal set. Port 1 DUT Adapter B Port 2 4. Measure DUT without cal adapter.

76 Thru-Reflect-Line (TRL) Calibration We know about Short-Open-Load-Thru (SOLT) calibration... What is TRL? A two-port calibration technique Good for noncoaxial environments (waveguide, fixtures, wafer probing) Uses the same 12-term error model as the more common SOLT cal Uses practical calibration standards that TRL was developed for noncoaxial microwave are easily fabricated and characterized Two variations: TRL (requires 4 receivers) measurements and TRL* (only three receivers needed) Other variations: Line-Reflect-Match (LRM), Thru-Reflect-Match (TRM), plus many others

77 Agenda What measurements do we make? Network analyzer hardware Error models and calibration Example measurements Appendix

78 Frequency Sweep - Filter Test CH1 S 21 log MAG 10 db/ REF 0 db CH1 S 11 log MAG 5 db/ REF 0 db Cor 69.1 db Stopba nd rejectio n START MHz STOP MHz Cor CENTER MHz CH1 S21 log MAG 1 db/ REF 0 db m1: GHz db m2-ref: GHz 0.00 db ref 2 SPAN MHz Return loss Insertion loss Cor x2 1 2 START MHz STOP MHz

79 Optimize Filter Measurements with Swept-List Mode PRm CH1 S21 log MAG 12 db/ REF 0 db Segment 3: 29 ms (108 points, -10 dbm, 6000 Hz) Linear sweep: 676 ms (201 pts, 300 Hz, -10 dbm) Swept-list sweep: 349 ms (201 pts, variable BW's & power) PASS Segment 1: 87 ms (25 points, +10 dbm, 300 Hz) Segment 5: 129 ms (38 points, +10 dbm, 300 Hz) START MHz STOP MHz Segments 2,4: 52 ms (15 points, +10 dbm, 300 Hz)

80 Power Sweeps - Compression Output Power (dbm) Compression region Linear region (slope = small-signal gain) Saturated output power Input Power (dbm)

81 Power Sweep - Gain Compression CH1 S21 1og MAG 1 db/ REF 32 db db 12.3 dbm db compression: input power resulting in 1 db drop in gain START -10 dbm CW MHz STOP 15 dbm

82 AM (db) PM (deg) Amplitude AM to PM Conversion Measure of phase deviation caused by amplitude variations Power sweep Mag(Am i n ) DUT AM can be undesired: supply ripple, fading, thermal AM can be desired: modulation (e.g. QAM) Test Stimulus Time Amplitude Q AM - PM Conversion = Mag(Pm ) (deg/d out Mag(Am B) in ) AM (db) PM (deg) Output Response Time Mag(AM o ut ) Mag(Pm o ut ) AM to PM conversion can cause bit errors I

83 Measuring AM to PM Conversion 1:Transmission Log Mag 1.0 db/ Ref db 2:Transmission /M Phase 5.0 deg/ Ref deg Ch1:Mkr dbm db Ch2:Mkr db 0.86 deg 1 2 Use transmission setup with a power sweep Display phase of S21 AM - PM = 0.86 deg/db 2 Start dbm Start dbm 1 CW MHz CW MHz 1 Stop 0.00 dbm Stop 0.00 dbm

84 Agenda What measurements do we make? Network analyzer hardware Error models and calibration Example measurements Appendix Advanced Topics time domain frequency-translating devices high-power amplifiers extended dynamic range multiport devices in-fixture measurements crystal resonators balanced/differential Inside the network analyzer Challenge quiz!

85 Time-Domain Reflectometry (TDR) What is TDR? time-domain reflectometry analyze impedance versus time distinguish between inductive and capacitive transitions With gating: analyze transitions analyzer standards inductive transition impedance Zo capacitive transition non-zo transmission line time

86 TDR Basics Using a Network Analyzer start with broadband frequency sweep (often requires microwave VNA use inverse-fourier transform to compute time-domain resolution inversely proportionate to frequency span Time Domain Frequency Domain F -1 CH1 S22 Re 50 mu/ REF 0 U t f Cor 20 GHz 6 GHz t 0F(t)*dt Integrate 1/s*F(s) TDR F -1 t f CH1 START 0 s STOP 1.5 ns

87 Time-Domain Gating TDR and gating can remove undesired reflections (a form of error correction) Only useful for broadband devices (a load or thru for example) Define gate to only include DUT CH1 S11&M log MAG 5 db/ REF 0 db Use two-port calibration PRm Cor CH1 MEM Re 20 mu/ REF 0 U PRm Cor RISE TIME ps mm 1 1: mu 638 ps 2: mu 668 ps 3: mu 721 ps Gate 2 1: db GHz 2: db GHz 2 3 CH1 START 0 s Thru in time domain STOP 1.5 ns 1 START GHz Thru in frequency domain, with and without gating STOP GHz

88 Ten Steps for Performing TDR 1. Set up desired frequency range (need wide span for good spatial resolution) 2. Under SYSTEM, transform menu, press "set freq low pass" 3. Perform one- or two-port calibration 4. Select S11 measurement * 5. Turn on transform (low pass step) * 6. Set format to real * 7. Adjust transform window to trade off rise time with ringing and overshoot * 8. Adjust start and stop times if desired 9. For gating: set start and stop frequencies for gate turn gating on * adjust gate shape to trade off resolution with ripple * 10. To display gated response in frequency domain * If using turn two transform channels off (even (leave if coupled), gating these on) parameters * must be set independently change format second to log-magnitude channel *

89 Time-Domain Transmission RF Input RF Output Main Wave Leakage CH1 S21 log MAG 15 db/ REF 0 db Cor Triple Travel CH1 S21 log MAG 10 db/ REF 0 db Cor RF Leakage Surface Wave Triple Travel Gate off Gate on START -1 us STOP 6 us

90 Time-Domain Filter Tuning Deterministic method used for tuning cavity-resonator filters Traditional frequencydomain tuning is very difficult: lots of training needed may take 20 to 90 minutes to tune a single filter Need VNA with fast sweep speeds and fast timedomain processing

91 Filter Reflection in Time Domain Set analyzer s center frequency = center frequency of the filter Measure S 11 or S 22 in the time domain Nulls in the time-domain response correspond to individual resonators in filter

92 Tuning Resonator #3 Easier to identify mistuned resonator in time-domain: null #3 is missing Hard to tell which resonator is mistuned from frequencydomain response Adjust resonators by minimizing null Adjust coupling apertures using the peaks in-between the dips

93 Frequency-Translating Devices Medium-dynamic range measurements (35 db) 8753ES 1 2 Ref In Attenuator Filter Attenuator FREQ OFFS ON off LO MENU DOWN CONVERTER UP CONVERTER RF > LO High-dynamic range measurements (100 db) 8753ES Ref in Ref out Reference mixer Start: 900 MHz Stop: 650 MHz Fixed LO: 1 GHz LO power: 13 dbm Start: 100 MHz Stop: 350 MHz RF < LO VIEW MEASURE RETURN Filter Attenuator CH1 CONV MEAS log MAG 10 db/ REF 10 db Attenuat or DUT Attenuator START MHz STOP MHz ESG-D4000A Powe r splitt er

94 High-Power Amplifiers 8753ES Preamp Ref In Source Preamp AUT DUT R A B AUT +43 dbm max input (20 watts!) 8720ES Option A High-Power Amplifier Test System

95 High-Dynamic Range CH1 MEM LOG 15 db/ REF 3 db Measurements CH2 MEM LOG 15 db/ REF 3 db PRm Cor Avg 10 PRm Standard 8753ES Cor Avg ES Special Option H16 CH1 START MHz CH2 START MHz STOP MHz STOP MHz

96 Multiport Device Test 8753 H39 CH1 S 21 log MAG 10 db/ REF 0 db 1_ db CH2 S 12 log MAG 10 db/ REF 0 db 1_ db MHz PRm Duplexer Test - Tx-Ant and Ant-Rx Cor 1 1 Hld PASS MHz PRm Cor PASS Hld CH1 START MHz STOP MHz CH2 START MHz STOP MHz 2 Multiport analyzers and test sets: improve throughput by reducing the number of connections to DUTs with more than two ports allow simultaneous viewing of two paths (good for tuning duplexers) include mechanical or solid-state switches, 50 or 75 ohms degrade raw performance so calibration is a must (use two-port cals whenever possible) Agilent offers a variety of standard and custom multiport analyzers and test sets

97 87050E/87075C Standard Multiport Test Sets For use with 8712E family 50 Ω: 3 MHz to 2.2 GHz, 4, 8, or 12 ports 75 Ω: 3 MHz to 1.3 GHz, 6 or 12 ports Test Set Cal and SelfCal dramatically improve calibration times Systems offer fully-specified performance at test ports Once a month: perform a Test Set Cal with external standards to remove systematic errors in the analyzer, test set, cables, and fixture Test Set Cal Fixture SelfCal DUT Once an hour: automatically perform a SelfCal using internal standards to remove systematic errors in the analyzer and test set

98 Test Set Cal Eliminates Redundant Connections of Calibration Standards Reflection Connections Through Connections 12-port 12-port 8-port 8-port 4-port 4-port Test Set Cal Traditional VNA Calibration

99 In-Fixture Measurements Measurement problem: coaxial calibration plane is not the same as the in-fixture measurement plane Calibration plane Measurement plane Fixture E D E S DUT E T Error correction with coaxial calibration Loss Phase shift Mismatch

100 Characterizing Crystal Resonators/Filters E5100A/B Network Analyzer Ch1 Z: R phase 40 / REF 0 1: U MHz Min Cor 1 START MHz SEG START STOP POINTS POWER IFBW STOP MHz MHz MHz dbm 200Hz > MHz END MHz dbm 200Hz Example of crystal resonator measurement

101 Balanced-Device Measurements ATN-4000 series (4-port test set + software) measure tough singled-ended devices like couplers measure fully-balanced or single-ended-to-balanced DUTs characterize mode conversions (e.g. common-to-differential) incorporates 4-port error correction for exceptional accuracy works with 8753ES and 8720ES analyzers more info at Channel Partner

102 Traditional Scalar Analyzer Incident DUT Transmitted SOURCE Reflected processor/display source INCIDENT (R) REFLECTED (A) SIGNAL SEPARATION TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY Example: 8757D/E requires external detectors, couplers, bridges, splitters good for low-cost microwave scalar applications RF R A B RF R A B Detector Detector Reflection Bridge DUT Termination DUT Detector Transmission

103 Directional Coupler Directivity Coupling Factor (fwd) x Loss (through arm) Directivity = Isolation (rev) Directivity (db) = Isolation (db) - Coupling Factor (db) - Loss (db) 50 db 20 db Examples: Test port Directivity = 50 db - 20 db = 30 db 50 db 30 db 10 db Test port Directivity = 50 db - 30 db - 10 db = 10 db 60 db 20 db 10 db Test port Directivity = 60 db - 20 db - 10 db = 30 db

104 One Method of Measuring Coupler Directivity 1.0 (0 db) (reference) Coupler Directivity 35 db (.018) Source short.018 (35 db) (normalized) Directivity = 35 db - 0 db = 35 db Source load Assume perfect load (no reflection)

105 Directional Bridge 50 Ω 50 Ω Detector 50 Ω Test Port 50-ohm load at test port balances the bridge -- detector reads zero Non-50-ohm load imbalances bridge Measuring magnitude and phase of imbalance gives complex impedance "Directivity" is difference between maximum and minimum balance

106 NA Hardware: Front Ends, Mixers Versus Samplers SOURCE INCIDENT (R) Incident Reflected REFLECTED (A) DUT SIGNAL SEPARATION TRANSMITTED (B) RECEIVER / DETECTOR Transmitted PROCESSOR / DISPLAY ADC / DSP Sampler-based front end S ADC / DSP Mixer-based front end It is cheaper and easier to make broadband front ends using samplers instead of mixers Harmonic generator f frequency "comb"

107 Three Versus Four-Receiver Analyzers Source Source Transfer switch Transfer switch R R1 A B A B R2 Port 1 Port 2 3 receivers more economical TRL*, LRM* cals only includes: 8753ES 8720ES (standard) Port 1 Port 2 4 receivers more expensive true TRL, LRM cals includes: 8720ES (option 400) 8510C

108 Why Are Four Receivers Better Than Three? TRL TRL* TRL* 8720ES Option 400 adds fourth sampler, allowing full TRL calibration assumes the source and load match of a test port are equal (port symmetry between forward and reverse measurements) this is only a fair assumption for three-receiver network analyzers TRL four receivers are necessary to make the required measurements TRL and TRL* use identical calibration standards In noncoaxial applications, TRL achieves better source and load match correction than TRL* What about coaxial applications? SOLT is usually the preferred calibration method coaxial TRL can be more accurate than SOLT, but not commonly used

109 Challenge Quiz 1. Can filters cause distortion in communications systems? A. Yes, due to impairment of phase and magnitude response B. Yes, due to nonlinear components such as ferrite inductors C. No, only active devices can cause distortion D. No, filters only cause linear phase shifts E. Both A and B above 2. Which statement about transmission lines is false? A. Useful for efficient transmission of RF power B. Requires termination in characteristic impedance for low VSWR C. Envelope voltage of RF signal is independent of position along line D. Used when wavelength of signal is small compared to length of line E. Can be realized in a variety of forms such as coaxial, waveguide, microstrip 3. Which statement about narrowband detection is false? A. Is generally the cheapest way to detect microwave signals B. Provides much greater dynamic range than diode detection C. Uses variable-bandwidth IF filters to set analyzer noise floor D. Provides rejection of harmonic and spurious signals E. Uses mixers or samplers as downconverters

110 Challenge Quiz (continued) 4. Maximum dynamic range with narrowband detection is defined as: A. Maximum receiver input power minus the stopband of the device under te B. Maximum receiver input power minus the receiver's noise floor C. Detector 1-dB-compression point minus the harmonic level of the source D. Receiver damage level plus the maximum source output power E. Maximum source output power minus the receiver's noise floor 5. With a T/R analyzer, the following error terms can be corrected: A. Source match, load match, transmission tracking B. Load match, reflection tracking, transmission tracking C. Source match, reflection tracking, transmission tracking D. Directivity, source match, load match E. Directivity, reflection tracking, load match 6. Calibration(s) can remove which of the following types of measurement A. Systematic and drift B. Systematic and random C. Random and drift D. Repeatability and systematic E. Repeatability and drift

111 Challenge Quiz (continued) 7. Which statement about TRL calibration is false? A. Is a type of two-port error correction B. Uses easily fabricated and characterized standards C. Most commonly used in noncoaxial environments D. Is not available on the 8720ES family of microwave network analyzers E. Has a special version for three-sampler network analyzers 8. For which component is it hardest to get accurate transmission and reflection measurements when using a T/R network analyzer? A. Amplifiers because output power causes receiver compression B. Cables because load match cannot be corrected C. Filter stopbands because of lack of dynamic range D. Mixers because of lack of broadband detectors E. Attenuators because source match cannot be corrected 9. Power sweeps are good for which measurements? A. Gain compression B. AM to PM conversion C. Saturated output power

112 Answers to Challenge Quiz 1. E 2. C 3. A 4. B 5. C 6. A 7. D 8. B 9. E