Network Analyzer Basicsy

1

What types of devices are tested?What types of devices are tested?H

i

g

h

DuplexersDiplexersFiltersCouplers

RFICsMMICsT/R modulesTransceiversCouplers

BridgesSplitters, dividersCombiners

Transceivers

ReceiversTuners

IsolatorsCirculatorsAttenuators

Converters

VCAs

gration

Antennas

Switches

AdaptersOpens, shorts, loadsDelay linesCables

Amplifiers

VCOsVTFs

Integ SwitchesMultiplexers

MixersSamplers

CablesTransmission linesWaveguideResonators

VTFsOscillatorsModulatorsVCAtten's

o

w

Multipliers

Diodes

DielectricsR, L, C's Transistors

2Device type ActivePassive

L

o

E l Wh M t h i I t tExample Where Match is Important

KPWR

FM 97

KPWR

FM 97 RR

Wire and bad antenna (poor match at 97 MHz) results in

Proper transmission line and antenna results in 1500 W radiated power -

150 W radiated power signal is received about three times further!

3Good match between antenna and RF amplifier is extremely important to radio stations to get maximum radiated power

Th N d f B th M it d d PhThe Need for Both Magnitude and Phase

Complete characterization of 1. SS 11

21

22

S

4. Time Domain Characterization

linear networksS

S

S 11 22

12

Complex impedance needed to d i t hi i it

Mag2.design matching circuits

Time

Vector Accuracy Enhancement

E

5.High Frequency Transistor Model

Error

MeasuredCollectorBase

4Complex values needed for device modeling

3. ActualEmitter

Hi h F D i Ch t i tiHigh-Frequency Device CharacterizationLightwave Analogy

Incident dReflected

TransmittedReflected

5

Smith Chart Review90o+jX

Polar plane

.4.6

.8

1.0

0 +R

Polar plane

0o180o+-

.20 R

-90 o

-jXRectilinear impedance plane 90p p

Constant X

Smith Chart maps rectilinear impedanceZ = ZoL

= 0 Constant R

Z ( )Z 0 ( h t)p p

plane onto polar planeZ = L

= 0 O1(open)

LZ = 0

= 180 O1

(short)

6

Smith Chart

Power TransferRS

RLFor complex impedances, maximum power

)

transfer occurs when ZL = ZS* (conjugate match)

0,81

1,2

o

r

m

a

l

i

z

e

d

)

Zs = R + jX

0,20,40,6

d

P

o

w

e

r

(

n

00,

0 1 2 3 4 5 6 7 8 9 10

L

o

a

d

RL / RS ZL = Zs* = R - jX

7

Maximum power is transferred when RL = RS

Transmission Line Review

Low frequencies Iow eque c es Wavelength >> wire length Current (I) travels down wires easily for efficient power transmission

I

y p Voltage and current not dependent on position

Hi h f iHigh frequencies Wavelength or

T i i Li T i t d ith ZTransmission Line Terminated with Zo

Zs = ZoZo = characteristic impedance of transmission line

Zo

VincVrefl = 0! (all the incident power is absorbed in the load)

9

For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line

T i i Li T i t d ith Sh t OTransmission Line Terminated with Short, Open

Zs = Zo

VVinc

Vrefl In phase (0 ) for openOut of phase (180 ) for shortoo

10

For reflection, a transmission line terminated in a short or open reflects all power back to source

T i i Li T i d i h 25 Transmission Line Terminated with 25

Zs = Zo

ZL = 25

VVinc

Vrefl

11Standing wave pattern does not go to zero as with short or open

Hi h F D i Ch t i tiHigh-Frequency Device Characterization

IncidentTransmitted

Reflected

TransmittedR B

TRANSMISSIONREFLECTIONA

TransmittedIncident

ReflectedIncident

AR=

BR=c de t

Group

Incident

Return

R

Gain / Loss

S-ParametersS21 S12

Delay

Transmission

Insertion Phase

SWR

S-ParametersS11,S22 Reflection

Impedance, Admittance

ReturnLoss

12

S21,S12 TransmissionCoefficient

Coefficient R+jX, G+jB

Reflection ParametersZL ZOReflection Vreflected = L OZL + OZ

ReflectionCoefficient =

reflected

Vincident=

= Return loss = -20 log(),Voltage Standing Wave Ratio

EVSWR = Emax

E=

1 + EmaxEmin 1 +

No reflection Full reflection

Emin 1 - No reflection

(ZL = Zo)

Full reflection(ZL = open, short)

dBRL

0 10 dB

13

RLVSWR1

Transmission ParametersVV VTransmittedVIncident

DUT

VTransmittedTransmission Coefficient = = VTransmittedVIncident

=

Insertion Loss (dB) = 20 LogV Trans

= 20 log Insertion Loss (dB) = - 20 Log V Inc

= - 20 log

Gain (dB) = 20 LogV Trans

= 20 log 14

Gain (dB) 20 Log V Inc

20 log

L F N t k Ch t i tiLow-Frequency Network Characterization

H-parameters Y-parameters Z-parametersH parametersV1 = h11I1 + h12V2V2 = h21I1 + h22V2

Y parametersI1 = y11V1 + y12V2I2 = y21V1 + y22V2

Z parametersV1 = z11I1 + z12I2V2 = z21I1 + z22I2V2 = h21I1 + h22V2 I2 = y21V1 + y22V2 V2 = z21I1 + z22I2

h11 = V1I1 ( i h t i it)I1 V2=0h12 = V1

(requires short circuit)

V2 I1=0 (requires open circuit)

15

All of these parameters require measuring voltage and current (as a function of frequency)

Limitations of H Y Z ParametersLimitations of H, Y, Z Parameters(Why use S-parameters?)( y p )

H,Y, Z parametersd l l d d h h Hard to measure total voltage and current at device ports at high

frequenciesA ti d i ill t lf d t t ith h t / Active devices may oscillate or self-destruct with shorts / opens

S-parameters Relate to familiar measurements(gain loss reflection coefficient ) Relate to familiar measurements(gain, loss, reflection coefficient ...) Relatively easy to measure Can cascade S-parameters of multiple

Incident TransmittedS21a1 b2Ca cascade S pa a ete s o u t p edevices to predict system performance Analytically convenient

S11Reflected S22

Reflectedb1

b2

a 2

DUTPort 1 Port 2y y

CAD programsFlow-graph analysis

Transmitted Incidentb1 a 2

S12b1 = S11 a1 +S12 a2b S S

16

Can compute H, Y,or Z parametersfrom S-parameters if desired

b2 = S21 a1 + S22 a2

ScatteringParametersScatteringParameters

Athighfrequencies,Z,Y,h &ABCDparametersaredifficult(ifnotimpossible)tomeasure.

o V andI arenotuniquelydefinedo Evenifdefined,V andI areextremelydifficult

to measure (particularly I)tomeasure(particularlyI).o Requiredopenandshortcircuitconditionsare

oftendifficulttoachieve.

Scattering(S)parametersareoftenthebestrepresentationformultiportnetworksathighfrequency.

17

ScatteringParameters(cont.)ScatteringParameters(cont.)Sparametersaredefinedassumingtransmissionlinesareconnectedtoeachport.g p

1 21a 2a

1 2

z z

1

1b 2b01 1,Z 02 2,Z

O h t i i li

1z 2zLocalcoordinates

Oneachtransmissionline:

0 0i i i iz zi i i i i i iiV zV z V e V e V z

0 0

i i i ii

ii

i

V z V zI z

Z Z

1, 2i

0 0i i

0i i i i ia z V z Z Incoming wave function18

0i i i i ib z V z Z Outgoing wave function

ForaOneForaOnePortNetworkPortNetwork

011 0 ZV L

01

01

1

1

00L

ZZ

VV

1a1b

01Z

1 0b 1l 1 0a

1 1

11 1

0 0

0Lb a

S a

Foraoneportnetwork,S11 isdefinedtobethesame as

11S 11 1 0S a sameasL.

0i i i i ia z V z Z Incoming wave function 0i i i i ib z V z Z Outgoing wave function

19

ForaTwoForaTwoPortNetworkPortNetwork

a1 21

a

1b 2b2a

01 1,Z 02 2,Z

1z 2z

Scattering 1 11 1 12 20 0 0b S a S a Scatteringmatrix 2 21 1 22 20 0 0b S a S a

1 11 12 1

000

0b S S a

b S ab S S 2 21 22 2 00b S S a

20

ScatteringParametersScatteringParameters

1 11 1 12 20 0 0b S a S a 2 21 1 22 20 0 0b S a S a

Outputismatched inputreflectioncoef.

11100

bS

a

Inputis

pw/outputmatched

t i i f

21 0

1

0

0

aa

bS

matched reversetransmissioncoef.

w/inputmatched

1

122 0

0

0

a

Sa

b

forwardtransmissioncoef.w/outputmatched

2

221

1 0

00

a

bS

a Outputis

matched

outputreflectioncoef.w/inputmatched

222 2 000

a

bS

a Inputismatched / p

12 0a

21

ScatteringParameters(cont.)ScatteringParameters(cont.)Whyarethewavefunctions(a andb)definedastheyare?

1 21a

b b2a

01 1,Z 02 2,Z

1z 2z1b 2b

*2

01 10 Re 0 0 ii i iV

P V I

(assuminglosslesslines) 0

0 Re 0 02 2i i i i

P V IZ ( g )

Note: 00 0i i ia V Z 210 0

2i iP a

22

ScatteringParameters(cont.)ScatteringParameters(cont.)

Similarly,

2

0

201 002

12

ii i

i

VP b

Z

0i

Also,

0 i ili i il

V l V e 0 i ili i iV l eV

2 2 21 1 02 2

i ili i i i iP l a l a e

2 2 21 12

02

i ili i i i il bP l b e

23

Measuring S-ParametersgIncident TransmittedS 21a 1

b 2

S 11Reflected

b

a 1Z 0

Loada 0

DUTForward

S Reflected b1

b 1 a2 = 0

S 11 = ReflectedIncident

= 1a 1 a2 = 0

S Transmittedb

2

S 22 = ReflectedIncident

=b2a 2 a1 = 0

S 21 =Incident

= 2a 1 a2 = 0 S 12 =Transmitted

Incident=

b1

a 2 a1 = 0

S 22b2a1 = 0

DUTZ 0 R

IncidentTransmitted S 12

22Reflected

a2

DUTZ 0Load

Reverse

24

1IncidentTransmitted S 12

b

SSParameterMeasurementsParameterMeasurements

Sparameters are typically measured, at microwave frequencies,S parametersaretypicallymeasured,atmicrowavefrequencies,withanetworkanalyzer(NA).

Theseinstrumentshavefoundwide,almostuniversal,applicationsincethemidtolate1970s.

Vectornetworkanalyzer:MagnitudesandphasesoftheSparametersaremeasured.

Scalarnetworkanalyzer:OnlythemagnitudesoftheSparametersismeasured.

25

VectorNetworkAnalyzer(VNA)VectorNetworkAnalyzer(VNA)

aPort1 1a

1b

DUT

1b

HewlettPackard8510 2bDUT

2a

26

Network Analysis of VNA MeasurementNetwork Analysis of VNA MeasurementNetworkAnalysisofVNAMeasurementNetworkAnalysisofVNAMeasurement

1a 1b 2a 2b

27

SSParameterMeasurementsParameterMeasurements

Port 1 Port 21ma 2

ma

2mb1mb

Meas. plane 1 Meas. plane 2Ref. plane Ref. plane

Errorboxescontaineffectsof test cables connectors couplersoftestcables,connectors,couplers,

28

SSParameterMeasurements(cont.)ParameterMeasurements(cont.)

21AS 12BS1 21S 1 1

1ma 21

11AS

22AS 22

BS

12

11BS

1

11S

21

22S

1 12mb

12AS 21

BS1 12S 11mb 2

ma

21 12 21 12A A B BS S S S

Assume error boxes are reciprocaland

" " .A BS S andWe need to calibrate to find

A BS S S dIf are known we can extract from measurements A BS S S andIf are known we can extract from measurements.This is called deembedding Thisiscalled deembedding.

29

CalibrationCalibrationShort,open,matchcalibrationprocedure

1ma

121S

S

1

Connect SC OC Z0

1mb

11S

22S Connect

-1 +10

0

h t t h

,A B Calibrationloads112S1 short open match

2S

2111 11

222

1SCm

SS S

S

3( , , )m m mS S S

measurements :21 12

11L

inS SS 221

11 11221OC

mS

S SS

11 11 11

( , , )

3SC OC match

S S S unknowns for each port :

11221

inLS

11 11matchmS S 11 21 22, ,S S S

30

Generalized Network Analyzer Block Diagram

Incident Transmitted

DUT

SOURCE Reflected

SIGNAL

REFLECTED(A)

TRANSMITTED(B)

INCIDENT (R)

SEPARATION

RECEIVER / DETECTOR

(A) (B)(R)

RECEIVER / DETECTOR

31PROCESSOR / DISPLAY

Traditional Scalar Analyzer

Traditional scalar system consists of processor/display and source

Example: HP 8757D requires external detectors, couplers, bridges, splittersrequires external detectors, couplers, bridges, splitters good for low-cost microwave scalar applications

RF R A BRF R A B

Detector

B id

Detector

Detector

32

DUT

BridgeTermination

Reflection TransmissionDUT

M d S l A lModern Scalar AnalyzerE thi f t i i d fl ti t iEverything necessary for transmission and reflection measurements isinternal!

One-port (reflection) and response (transmission) calibrations

Narrowband and broadband detectorsLarge display

33Synthesized source Transmission/reflection test set

Spectrum Analyzer / Tracking Generator

RF in

IFIFLO

DUT

8563A SPECTRUM ANALYZER 9 kHz - 26.5 GHz

TG out

Spectrum analyzer

DUT

Tracking generatorf = IF

DUT

Key differences from network analyzer: one channel -- no ratioed or phase measurements one channel no ratioed or phase measurements More expensive than scalar NA Only error correction available is normalization

34

Poorer accuracy Small incremental cost if SA is already needed

Modern Vector AnalyzerFeatures:Synthesizer

15 MHz to 60 MHzintegrated sourcesampler-based front endtuned receiverMUX

996 kHz

tuned receivermagnitude and phasevector-error correction

A S4 kHz

TestSet

RF

300 kHz

Reference

detector

T/R or S-parameter test setsB S 4 kHz

4 kHz

to3 GHz

Phase R S

4 kHzLock

ADC CPU DisplayDUT

ADC CPU Display

Digital Control

N t d l l lik HP 8711/13C l k j t lik t l

Source ReceiverTestSet

35

Note: modern scalar analyzers like HP 8711/13C look just like vector analyzers, but they don't display phase

T/R Versus S-Parameter Test SetsTransmission/Reflection Test Set S-Parameter Test Set

Source Source

Transfer switch

B

R

A B

R

ABA BA

Port 1 Port 2

DUTFwd

Port 1 Port 2

DUTFwd Rev

RF always comes out port 1 port 2 is always receiver

RF comes out port 1 or port 2 forward and reverse measurements

36

port 2 is always receiver response, one-port cal available

forward and reverse measurements two-port calibration possible

Processor / Display

Incident Transmitted

HACTIVE CHANNEL

RESPONSE

ENTRY

NETWORK ANALYZER50 MHz-20GHz

SIGNAL

SOURCE

Incident

Reflected

Transmitted

DUT

STIMULUS INSTRUMENT STATE R CHANNEL

R LT S

HP-IB STATUS

RECEIVER / DETECTOR

REFLECTED(A)

TRANSMITTED(B)

INCIDENT (R)

SIGNALSEPARATION

PORT 2PORT 1

PROCESSOR / DISPLAY

markers limit lines pass/fail indicators linear/log formats

37

grid/polar/Smith charts

M t E M d liMeasurement Error ModelingSystematic errors

due to imperfections in the analyzer and test setup are assumed to be time invariant (predictable) can be characterized (during calibration process) and mathematicallycan be characterized (during calibration process) and mathematically

removed during measurementsRandom errors

vary with time in random fashion (unpredictable) cannot be removed by calibration main contributors:main contributors:

instrument noise (source phase noise, IF noise floor, etc.) SYSTEMATIC

Errors:

switch repeatabilityconnector repeatability

Drift errors

Unknown Device

Measured Data RANDOM

DRIFTDrift errors are due to instrument or test-system performancechanging after a calibration has been done

DRIFT

38

are primarily caused by temperature variation can be removed by further calibration(s)

S t ti M t ESystematic Measurement Errors

A BCrosstalkR CrosstalkDirectivity

DUT

Source LoadFrequency response

reflection tracking (A/R)Mismatch Mismatch transmission tracking (B/R)

39

Six forward and six reverse error terms yields 12 error terms for two-port devices

Types of Error CorrectionTwo main types of error correction:

response (normalization)p ( )simple to performonly corrects for tracking errorsy gstores reference trace in memory,then does data divided by memory thruy y

vectorrequires more standardsqrequires an analyzer that can measure phaseaccounts for all major sources of systematic erroraccounts for all major sources of systematic error

SHORT

S11AOPEN

LOAD

thru

40

S11MLOAD

Wh t i V t E C ti ?What is Vector-Error Correction? Process of characterizing systematic error terms

measure known standardsremove effects from subsequent measurementsremove effects from subsequent measurements.

1-port calibration (reflection measurements)only 3 systematic error terms measureddirectivity, source match, and reflection tracking

Full 2-port calibration( fl d )(reflection and transmission measurements)

12 systematic error terms measuredusually requires 12 measurements on four known standards (SOLT)usua y equ es easu e e ts o ou ow sta da ds (SO )

Some standards can be measured multiple times(e.g., THRU is usually measured four times) Standards defined in cal kit definition file

network analyzer contains standard cal kit definitionsCAL KIT DEFINITION MUST MATCH ACTUAL CAL KIT USED!

41

Reflection: One-Port ModelIdeal

If you know the systematic error terms, you can solvefor the actual S-parameter

S S

RF infor the actual S parameter Assumes good termination at port two if testing two-port devices If port 2 is connected to the network analyzer and DUT reverse

S11M S11A isolation is low (e.g., filter passband):assumption of good termination is not valid

Error Adapter

two-port error correction yields better results

ED = DirectivityERT = Reflection tracking

1RF in

o dap e

ERT Reflection trackingES = Source Match

S11M = MeasuredS11M S11AESED

S11M = MeasuredS11A = ActualERT

42S11M = ED + ERT S11A

1 - ES S11A

To solve for S11A, we have 3 equations and 3 unknowns

B f d Aft O P t C lib tiBefore and After One-Port Calibration

0

Data BeforeE C ti

02.0

Error Correction20

B

) 1 1

40

L

o

s

s

(

d

B

W

R

1.1

R

e

t

u

r

n

L

V

S

W

1.01

Data AfterError Correction

60

R

1.001

436000 12000

Adapter Considerationsdesired signal

reflection from adapter

= total

adapter DUT+

Coupler directivity = 40 dB

leakage signal

TerminationAdapter DUT

Coupler directivity 40 dBDUT has SMA (f) connectors

Worst-case Ad ti f APC 7 t SMA ( )

APC-7 calibration done here

System Directivity

APC 7 to SMA (m)

Adapting from APC-7 to SMA (m)

28 dB APC-7 to SMA (m)SWR:1.06

17 dB APC-7 to N (f) + N (m) to SMA (m)SWR:1.05 SWR:1.25

4414 dBAPC-7 to N (m) + N (f) to SMA (f) + SMA (m) to (m)

SWR:1.05 SWR:1.25 SWR:1.15

T P t E C tiTwo-Port Error CorrectionPort 1 Port 2E

S21ES

ETTa1

A

X

b2 Forward modelS11

S12

S22ES

ED

ER

T

EL

1

b1A

A

Aa2

T= Directivity= Source Match= Reflection Tracking

= Load Match= Transmission Tracking= Isolation

ESED

ERT

ETT

EL

EX

A

Notice that each actual S-parameter is a

T

Notice that 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!!!

45

equations to use network analyzers!!!

Crosstalk (Isolation)

Crosstalk definition: signal leakage between portsg g pCan be a problem with:

High-isolation devices (e.g., switch in open position)DUT

High-dynamic range devices (some filter stopbands)Isolation calibration

Adds noise to error model (measuring noise floor of system)Only perform if really needed (use averaging)

if t lk i i d d t f DUT t h t t i tiif crosstalk is independent of DUT match, use two terminationsif dependent on DUT match, use DUT with termination on output

Isolation cal when crosstalk is dependent on match of DUT

46

DUT LOADDUTLOAD

Errors and Calibration Standards

UNCORRECTED RESPONSE 1-PORT FULL 2-PORT

SHORT SHORT SHORT

DUT OPEN OPEN OPENthru

ConvenientGenerally not accurateNo errors removed

DUT

LOAD LOAD LOAD

No errors removedEasy to performUse when highestaccuracy is not required

For reflection measurementsN d d f h h

DUT

DUT

thru

accuracy is not requiredRemoves frequencyresponse error

Need good termination for high accuracy with two-port devicesRemoves these errors:

Di ti it

Highest accuracyRemoves these errors:

DUT

DirectivitySource matchReflection tracking

DirectivitySource, load matchReflection trackingOther errors:

47

Transmission trackingCrosstalk

Random (Noise, Repeatability)Drift

C lib ti SCalibration Summary

S-parameter(two-port)

T/R(one-port)

Reflection Test Set (cal type)SHORT

Reflection trackingDirectivity

(two port)(one port)

OPEN

DirectivitySource matchL d t h

LOAD

S parameterT/R

Load match

T i iTest Set (cal type)

T i i T ki

S-parameter(two-port)

T/R(response, isolation)

Transmissionerror can be corrected

Transmission TrackingCrosstalkS t h *( )

error cannot be corrected* HP 8711C enhanced response cal can correct for source

48

Source matchLoad match

( )match during transmission measurements