HP AN8510 13_Measuring Non Insert Able Devices

8/14/2019 HP AN8510 13_Measuring Non Insert Able Devices

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Meas uring Non inse rtable

Devices

Product Note 8510-13

A new techn ique formeasuring componentsusing the HP 8510CNetwork Analyzer


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Introduct ionThe m ajority of devices used in

rea l-world microwave system s ar e

noninsert able because of the connec-tors employed. In the past , these

devices were theoretically not

measur able meaning that fully

tr aceable and verifiable dat a could

not be pr ovided. Now th e HP 8510C

with an S-para meter t est set offers

a new technique tha t provides

accur acy rivaling the best insert able

device measu rem ents. This note

reviews var ious m ethods used to

calibra te th e network an alyzer for

measur ement of noninsertable

devices and compa res th e results

an d uncerta inties of each meth od.

As shown in Figure 1, for a test

device to be insertable, both connec-

tors m ust be of the sam e connector

family, with one connector male,

and t he other female. When the test

device is inserta ble, th en th e mea-

sur ement port s can be connected

together t o establish the t hru

connection during tr ans mission

calibration. The configuration of

the measur ement test setup need

not be changed between tra nsmis-

sion calibra tion and actua lmeas ur ement of the test device.

Figure 1. Classes of Device Un derTest (DUT). For inser table devices,Port 1 connector t ype will mat e withPort 2 connector type. For reversibledevices, the same sex of the sa meconnector family are u sed on both Port1 and Port 2. Transitional devices useconn ectors of different families onPort 1 and P ort 2.

There a re two gener al types of

noninsert able test devices. The first ,

and probably the most prevalent,

is the reversible type of device.

A reversible device is one tha t h as

both connectors of the s am e family

and sex. Note th at devices with

herm aphr oditic connectors, like

precision 7 mm, are both inser ta ble

and reversible. The second cat egory

of noniserta ble devices is th e

tra nsitional type. With t ran sitional

devices, the connectors are of

different families, such as coaxialand wa veguide.

In t erms of measurement accura cy

and convenience, it would be desir-

able if all pur ely coaxial microwave

modules an d cables were configuredto be insert able. In systems using

coaxial cable to inter connect the

modules and subsystem s, it is

comm on for cables to use a ma le

connector on both en ds an d for t he

modules to u se female connectors

on all their port s. Often the design-

er is faced with the sam e measur e-

ment problem due to the fact

th at t he device by natu re is not

insertable becau se it is a coaxial to

waveguide tran sition. These non-

insert able configur at ions lead t o

test ing problems because t he deviceunder test m easurement specifica-

tions ar e seriously compr omised.

Why poorer specifications? Sim ply,

th e device cannot be inserted in t he

measur ement system using the

identical configur at ion in which t he

measur ing system alone was

calibra ted. The difference in s ystem

configur at ion between calibra tion

and measu rement pr oduces an

uncert aint y in the accuracy of the

results tha t can only be treated as

a ra ndom error ha ving an un knownmagnitude and pha se. This must

resu lt in an increa se in the specifi-

cation guardband causing unneces-

sary rejects, increased testing and

ana lysis time, and u ltimately an

increase in the cost of the device.

2


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Accuracy EnhancementAt microwave frequencies system -

atic effects such a s leaka ge, test

port mismatch, and frequencyresponse will produce uncerta inties

in the mea sur ed data . However, in a

stable measurement environment

these effects are repeatable and

can be measur ed by the net work

analyzer. This process is called

measurement calibrat ion. During

measurement calibrat ion a series

of known devices (stan dar ds) are

connected to the test ports a nd

measu red. The system atic effects

are determined as the difference

between the measur ed and the

known, or modeled, responses ofthe st an dar ds. Now the device

under test is measur ed. The

accuracy enhancement algorithm

uses an err or model of the n etwork

analyzer system to ma themat ically

relate these err ors t o the results of

the device measur ement an d thus

obtain values for the actua l

responses of the DUT.

Under ideal conditions, with per-

fectly known standards, systematic

effects would be complet ely cha ra c-

terized an d rem oved. The accur acyto which these standa rds a re known

establishes h ow well these s ystem-

atic errors can be cha ra cterized an d

removed. In fact, a well esta blished

figure of merit for a calibrat ed

system is the ma gnitude of the

residual systematic errors. These

residua l errors ar e the portion of

the uncorrected systematic errors

tha t r emain because of imperfect

modeling of the a ctual r esponse of

the calibration standar ds.

Error Mode lVector error correction techniques

can grea tly redu ce the effects of

directivity, crosstalk, source ma tch,and frequen cy response errors a s

well as t he mismat ch u ncerta inties

caused by the vector int era ction of

the input and output impedance of

the DUT with t he imperfect

source and load mat ch of the

measuring system. The HP 8510

12-term calibration and measur e-

ment model provides the h ighestaccur acy in comm on use t oday

(Figur e 2). This 12-term err or model

is used in both t he FULL 2-PORT

and th e TRL 2-PORT calibration

types offered in th e HP 8510C.

3

Figu re 2. 12-Term Erro r Model. The m ost sophisticated l2-term error m odel isrequired to account for t ran smission a nd reflection signal pa th r esponse andleakages, source and load mismat ch effects in tra nsmission measur ements, an dthe effect of an imperfect t ermina tion in reflection m easur ements.


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The Ideal CaseThe ideal case for m easur ement of a

2-port device provides best accuracy

an d complete tr aceable and verifi-able data (Figur e 3). This calibra -

tion pr ocedure uses an S-para meter

test set to measure an insertable

device. Steps 1 and 2 mea sur e

separ ate er ror ter ms for directivity,

source mat ch, and r eflection signal

pat h frequen cy response for both

test ports. Transm ission isolation is

measur ed with both ports t erminat-

ed. In step 3, the test ports are

connected together t o ma ke th e

thru a nd then measure separate

error term s for forward and r everse

load m atch and tra nsmission signalpat h frequency response.

Since the Port 1 and P ort 2 connec-

tion to accomplish th e thr u is th e

same a s will be used during the

meas ur ement , all error coefficientscan be obtained directly.

With the device connected, step 4,

the st imulus is applied to Port 1

and the forward par ameters, Sat

and Sol, are measu red. Then the

stimu lus is applied to Port 2 an d

the reverse parameter s, 522 and

Sir, are m easured. These measured

values, along with th e error t erms,

are used in the accuracy enhance-

ment algorithm to find the a ctual

device parameters with greatly

reduced uncerta inty.

In this application the thru does

not actua lly repr esent a ny specific

device, or th e special case of an

absence of any device at all. Thisis a basic principle of tran smission

measurement calibrat ion. The

tr ans mission reference is a zero-

length, zero-loss t ra nsm ission line.

Essen tially, Port 1 of the t est set is

connected directly to Port 2 of the

test set, then the ports ar e separat-

ed and t he device to be tested is

insert ed. Past pr actice has allowed

complete performance verification

with verifiable and t ra ceable speci-

fications only when t his is th e case.

If the device under test is notinsertable, then it is necessary to

use some sort of thr u device in order

to accomplish th e conn ection for

measurement of tran smission

response and load ma tch. This is

the pr oblem. With t he 12-term

calibrat ion procedur e, the thr u

connection is used to measur e the

tra nsmission signal path frequency

response and t he impedan ce of the

retu rn port . But what good does it

do to measu re th e frequency

response and load match error

terms when th e wrong adapter isinsta lled? During calibration, the

thru device is measured but it is

removed or chan ged for the a ctual

device measurement.

Due to impr ovement s in the

hardwar e and calibrat ion t ech-

niques, ther e are ways t o achieve

measurement results with accura cy

very near t o that wh ich is achiev-

able with t he ideal inserta ble case.

Now we will exam ine common

techniques for m easurement of

noninsert able devices and th e newHP 8510C adapter removal method.

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Figure 3. Ideal Case-2-Port Cal. Measurem ent of insert able devise using anS-param eter (two-path ) test set is the ideal case. All error terms can be measu redwith th e correct t est port connectors in place, and the device under test does notrequire physical reversal.


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Case 2

Mode ling the N on -Zero

ThruIf the char acterist ics of the thr u

device are k nown, acceptable m ea-

sur ement s can be made by modeling

the effect that t he thr u device has

upon m easurement of the system

err ors. In this met hod the difference

between t he connection used for

tr ans mission calibrat ion an d for

conn ection of th e DUT is m odeled

into a delay/thru t ype standard of

the H P calibrat ion kit definition by

specifying the insertion loss, electri-

cal length, an d impedance chara c-

terist ics of the thr u. If th e

delay/thr u model is exact, then th e

effect of the chan ge to the t est port s

is removed from th e error ter ms.

This technique can be very effective

if the magnitude, phase, and

impedance of the thr u connection is

modeled very a ccur ately, but ma y

not pr ovide su fficient corr ection of

the actua l effect of th e non-zero

thru u pon the magnitude and phase

of th e forwar d an d reverse load

ma tch term s. This will produce

errors in t he measu rement of lowloss devices.

Case 3

Complete Noninsertable

CalibrationThe m ost complete an d effective

calibrat ion procedure for nonin-

sert able devices is called adapter

removal. This technique (Figure 6)

requires an adapter that has the

sam e connector types a s th e device

under test a nd calibration stan -

dar ds for both connector t ypes. The

electr ical length of the ada pter

need only be specified within 1/4

wavelength a t ea ch frequency. The

current Hewlett-Packard Type-N,

3.5 mm , and 2.4 mm calibration kits

ar e supplied with t he in-fam ily

ada pters a lready defined for u se in

the adapter removal procedure. In

order to use any oth er ada pter, such

as a waveguide to coaxial tr ans i-

tion, the adapt er mu st be specified

as described in the box inset,

Specify the a dapt er, on pa ge 8.

The adapter removal algorithm uses

the r esults of the two cal sets a long

with th e nominal electr ical length of

the adapt er to compute t he actualS-para meters of the adapter. This

data is used to generate a separ ate

thir d cal set in which th e forwar d

and reverse match and tr acking

terms a re as if Port 1 an d Port 2

could actually be connected. This

is possible because th e actua l

S-para meters of the adapt er are

measu red with great accur acy,

allowing the effects of the ada pter

to be completely rem oved when th e

third cal set is generated.

6

Figure 6. Adapte r Removal Calibration. A 2-Port calibration (either F ULL 2-PORT or TRL 2-PORT) for each port , along with kn owledge of the nomin al lengthof the adapter, allow complete removal of the effects of the adapter from the errorcoefficient set.


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Perform the 2-PortCalibrationsTwo 2-Port calibrations ar e per-

form ed, first with t he ada pterconnected to Port 2, then with th e

ada pter connected to Port 1. The

resu lt of each calibration is stored

in a separ ate cal set. Note th at both

of th ese calibra tions are per form ed

using t he ideal zero-length, zero-

loss t hr u connection.

If the device ha s a waveguide port

and a coaxial port , there is an addi-

tional considera tion. For a typical

waveguide calibrat ion t he SET Z 0function u nder t he CAL menu is set

to 1; for th e typical coax calibra tionthe SET Z 0 function is set t o 50.

Be certain that the correct value

is enter ed before beginning ea ch

calibrat ion an d, if the Smith char t

is used, for impedance measu re-

ment a t th e appropriate ports of

the DUT.

Modify and Sa vethe New Cal SetWhen th e calibrat ions a re complete,

press CAL, MORE, MODIFY CAL

SET, then ADAPTER REMOVAL.

Now press CAL SET for PORT 1and specify the cal set u sed to store

the Port 1 calibration results; then

press CAL SET for PORT 2 and

specify the cal set u sed to store th e

Port 2 calibration result s. Next

specify the cal k it which contains

the definition of the adapt er by

pressing t he softkey labeled with

the cal kit n am e. Finally, press

MODIF Y & SAVE then specify a

separ at e cal set to contain th e new

err or coefficients. Th e er ror coeffi-

cients will be computed a nd st ored,

corr ection is tur ned on, and err or-corr ected data is displayed.

Verify th e CalibrationFollowing th e mu ltiple calibrat ions

and the a dapter r emoval procedure,

verify th e a ccur acy of the calibra-tions and the adapter removal algo-

rithm by measur ing the adapter.

Because th e adapter used during

calibrat ion has been math ematical-

ly removed from t he er ror coeffi-

cient set, the m easurement should

accurat ely represent t he actual

response of the a dapt er. This step

serves as a verificat ion of the

calibrat ion. If unexpected phas e

variat ions show up in the response

of the a dapt er (such as shown in

par t B of Figure 7) it is a sign th at

the electrical delay of the a dapt erwas n ot specified closely enough in

the cal kit definition.

Fortu nat ely, if the adapt er length

ha s n ot been s pecified corr ectly, it

is not necessar y to repeat th e two

2-Port calibrat ions. Simply chan ge

the ada pter offset delay specifica-

tion in the cal kit definition t o the

correct value and then repeat th e

menu sequence under adapter

removal.

7

Figure 7. Measu remen t of AdapterAfter Adapter Remo val. Par t A showsthe insertion phase of the ada pter afteradapt er removal. Par t B shows unex-pected phase tra nsitions which will bepresent if the electrical delay of theadapt er is not specified within 1/4wavelength at each frequency.


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Spec ify the AdapterIt is importa nt t o recognize th at t he

nominal electr ical delay of th e ada pter

mu st be k nown within 1/4 wavelengthat ea ch measur ement frequency. The

electrical delay of the ada pter mu st be

known because the adapter removal

cal-culat ions include tak ing a squar e root

of a complex number. In order to deter-

mine t he correct sign of the r oot, th e

algorithm u ses the adapter length t o

place the result in the correct quadrant.

The a dapt er s electrical length mu st be

enter ed into one of the H P 8510 cal kit

definitions.

Measure the AdapterMeasur e th e nominal electrical delay of

th e ada pter as follows:

1. With Port 1 configured so that t he

ada pter ma y be connected, perform a

simple Sat Response calibration at Port

1 desire a sh ort circuit.

2. Connect the adapter to Port 1 and

terminate th e adapter with a short

circuit.

3. Measur e the electr ical delay of the

adapter. Select PHASE, RESPONSE

MENU , ELECTRICAL DELAY,

th en a djust electr ical delay to achieve

a flat t ra ce. If th e adapt er is a wave-

guide device, select waveguide d elay

an d enter t he corr ect cutoff frequency.

One-half the meas ured electrical

delay value is the actu al nominal

length of th e adapt er. If the short

circuit used to terminate the adapter

is offset, rem ember t o subtra ct itselectrical length from the

measurement.

Modify the Cal Kit

Next, m odify one of th e cal kits t o

include this adapter definition as follows:

1. Select th e cal kit to include the

ada pter d efinition by pressing CAL ,

MORE, MODIFY .

2. Refer to th e cal kit St an dar d Assign-

ment ta ble in th e cal kit manua l and

choose an un used st an dar d, 20 forinstance. Press DEFINE STAN-

DARD , then enter 20, x1, then select

the sta ndard type by pressing

DELAY/THRU .

3. Ent er th e electr ical delay of the ada pt-

er by pressing SP ECIFY OFFS ET,

OFFS ET DE LAY, then entering the

value for electrical delay measured

above. If the a dapt er is a wa veguide

device, pr ess WAVEGUIDE , then

press MINIMUM FREQUE NCY

an d ent er t he cutoff frequen cy. Pr essSTD OFFSET DONE .

4. Next, enter a descriptive label for th e

adapter by pressing LABEL STAN-

DARD then using the knob and th e

Title menu. Pr ess TITLE DON E.

Now press STD DONE (DEFINED).

(It is not necessa ry to specify an y

oth er char acteristics of th e adap ter

except Offset Delay, Minimu m a nd

Maximum Fr equency, an d Coax or

Waveguide.)

5. Now press SP ECIFY CLASS ,

MORE, MORE, then SPECIFY:

ADAPTER and enter the s tandard

number of the adapt er, 20, x1.

Press CLASS DONE .

6. Enter an a ppropriate class label by

pressing LABEL CLASS, MORE,

MORE, ADAPTER then using the

Title menu .

7. Enter a n appr opriate label for th ecalibration kit by pressing LABEL

KIT an d defining the title using the

Title menu .

8. Finally, press KIT DONE (MODI-

FIED) to save th is new cal kit

definition

This cal kit is now ready to be used in

the adapter removal procedure.

8


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Results Using AdapterRemovalThe following plots sh ow compar -

isons of results obtained with va ri-ous techniques. Figure 8 is a way to

verify tha t th e adapter removal

algorith m works corr ectly. Fir st,

part (a) shows a 7 mm beaded air

line measured using the standar d

full 2-Port calibrat ion. The S21Frequency domain magnitude is a

typical r esponse for this type of

device. The S11 time band pass

domain measurement clearly shows

the internal beads that support th e

center conductor. Next, par t (b)

shows th e resu lts of two, 2-port

calibra tions combined us ing theadapter removal procedure, then

the sam e air line is measured.

Par t (c) shows measu rement of

the 7 mm to 7mm adapter used

in this sequence. It was m ade up

of a 7 mm to 3.5 mm m ale adap ter

connected t o a 3.5 mm fema le to

7 mm a dapter. Notice that it has

generally poorer retu rn loss and

a more complex intern al str ucture

than the air line.

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Figure 8. 7 mm Bead less Airline Comparisons. Measur ements of this deviceusing (a) the sta ndar d full 2-Port calibrat ion a nd (b) the adapt er rem oval calibrat ionshow corresponding results in both th e frequency and t he t ime domains. Very closeagreement is shown even though the ada pter is generally poorer quality than t hedevice under t est. Pa rt (c) shows the S11 frequency and t ime band pass domainmeasurements of the adapter.

(a) Frequency and Time Band Pass Res ults , Standard Ful l 2-PortCalibrations.

(b) Frequency and Time Ban d P ass Resu lts , Adapter Removal Cal ibration.

(c) Frequency and Time Band Pass Results , Adapter used in (b)


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Figure 9 compar es measur ements of

a low-loss 3.5 mm r eversible device

ma de by connecting 7 mm t o 3.5

mm female adapters to the air lineused in Figur e 8. For th e first four

plots, the a ir line is measu red after

switching between t he very equal,

high qua lity 3.5 mm ma le to female

an d female to female ada pters in

th e HP 85052B 3.5 mm calibrat ion

kit. In th e second set of four plots,

the sa me device is measur ed using

the a dapter r emoval with the 3.5

mm female to female ada pter. Since

th e test device is stable and the

adapters are h igh quality, there ar e

only minor differences between th e

two sets of results. In pa rt icular,note th e difference in th e time

domain traces obtained using

adapter removal where t he load

ma tch effects a re not rem oved as

well using the swap equa l adapter

technique.

A technique n ot shown here was

investigated t hat involved a combi-

na tion of a 2-port calibration an d a

simpler 1-port calibrat ion t o mea-

sure an d remove the adapt er.

Compa rison of test resu lts showed

that the load mat ch term in th ereverse dir ection was typically 6 dB

worse tha n th e HP 8510C adapter

removal procedure. Further investi-

gation showed this 2-port/1-port

procedure no better th an using the

swap ada pter t echnique with good

adapters and tha t the results were

str ongly affected when the ada pterexhibited poor m at ch. The HP 8510C

ada pter r emoval procedur e shows

no such dependence upon the

adapter match.

Note tha t th e HP 8510C adapter

removal procedure pr oduces a fully

error-corrected measurement of the

2-port device. The mea sur ement

resu lts of th e HP 8510C ada pter

removal procedure ar e tra ceable

to the extent th at the calibration

sta nda rds us ed for both of the

2-port calibrat ions ar e tra ceable.The actual un certa inties of the m ea-

surement a fter the adapter removal

procedure can be determ ined using

the sta ndard techniques applied to

2-port calibrat ions. It is n ecessar y

to factor in th e errors du e to inaccu-

ra cies of the calibrat ion sta ndar ds

once for each calibration.

In some applicat ions th e adapt er

removal procedur e ma y be less con-

venient sin ce two 2-port calibra-

tions ar e requir ed. However,adapt er rem oval can pr ovide a new

level of confidence even if you

choose to use the less a ccur at e tech-

nique of swap equal ada pters t o

measure the device under test.

Becaus e adapt er r emoval provides

an exact measurement of the

adapters, you obtain a realistic

value for the difference between

their length , loss an d impedance.

So, for mea sur ement s tha t do not

require verifiable accuracy, ada pter

removal ma y allow you t o use less

accurate calibration methods in theactual device measurement but

with a better idea of the actual

effects of the n on-zero thr u.

10


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11

Figure 9. Comparin g Calibration Metho ds. Compar ison of results m easur ing a3.5 mm r eversible device (port 1 female port 2 fema le) using a two-path test set:(a) shows switching between high qua lity adapter s; (b) shows new a dapter removalprocedure. Since the switched ada pters a re equa l, there is little difference betweenthe results.

(a) Results after SwappingBetween Equal Adapters.

(b) Results after AdapterRemoval Procedure.


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For more informat ion aboutHewlett-Packard test and measure-m e n t p r o d u c t s , a p p l ic a t i o n s , s e r -v i ce s , and for a current sa l e s

of f i ce l i s t ing , v i s i t our web s i t e ,http://www.hp.com/go/tmdir. Youcan also contact one of the followingc e n t e r s a n d a s k f o r a t e s t a n dmeasurement sales representative .

United States:Hewlett-Packard CompanyTest and Measu rement Call CenterP.O. Box 4026En glewood, CO 80155-40261 800 452 4844

Canada:Hewlett-Packard Canada Ltd.5150 Spectru m WayMississauga, OntarioL4W 5G1(905) 206 4725

Europe:Hewlett-PackardEuropean Marketing CentreP.O. Box 9991180 AZ AmstelveenThe Netherlands(31 20) 547 9900

Japan:Hewlett-Packard J apan Ltd.Measurement Assistance Center9-1, Takakura-Cho, Hachioji-Shi,Tokyo 192, J apa nTel: (81) 426-56-7832Fax: (81) 426-56-7840

Latin America:Hewlett-PackardLatin American Region Headquar ters5200 Blue La goon Dr ive, 9th F loorMiam i, Florida 33126, U.S.A.(305) 267 4245/4220

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Hong KongTel: (852) 2599 7777Fa x: (852) 2506 9285

Data Subject to ChangeCopyrigh t 1997Hewlett-Packard CompanyPrin ted in U.S.A. 11/975956-4373E

HP AN8510 13_Measuring Non Insert Able Devices

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Transcript of HP AN8510 13_Measuring Non Insert Able Devices