Middleton W.M. (ed.) Reference Data for Engineers: Radio, Electronics, Computer and Communications

11-4

TABLE

2.

RESISTANCE VALUES

FOR

ATTENUATOR PADS WHEN

R,

=

1

OHM'

I

0.7

1

0.040 274

I

12.395

I

0.080 678

I

24.830

I

0.083 927

I

11.915

1

0.040 274

1

24.830

*

These values have been multiplied

by

IO5.

NOTES:

1.

If

R,

#

1

ohm, multiply all values by

R,.

2.

For

other decibel values, use formulas

in

text.

ATTENUATORS

11-5

(A)

Tee

pod

1

/b

(B)

PI

pad.

(CJ

Srfdged

tee

pod.

0

(Dj

Bnlanced pad.

Fig.

5.

Symmetrical pads

for

use between equal characteristic

impedances.

chrome, cracked carbon, tantalum nitride)

on

an insu-

lating substrate (mica, ceramic, quartz) are used. Figs.

2,

3,

and

4

illustrate coaxial cross sections.

For a broadband match between impedances

R

and

R2,

use the minimum-loss L pad (Fig. 6).

Fig.

6.

Unsymmetrical matching pad between

R,

and

R2.

Power Dissipation Within a Tee

Pad

Table

4

lists values of power dissipation within a tee

pad. The values in the table

are

for an input of

1

watt;

for

other input powers, multiply the values in the table

by the input power.

CONNECTORS

Each connector of an attenuator must mate nonde-

structively with connectors that comply with the govern-

ing standard, typically Mil-C-39012, IEEE Std. 287-

1968, or Mil-F-3922,

as

shown in Table

5.

MEASUREMENT OF

ATTENUATION

The methods covered are fixed-frequency

,

broad-

band, and swept or stepped in frequency. All accuracies

exclude the effects of mismatch uncertainty and connec-

tor nonrepeatability. In Fig.

7,

the most commonly

used attenuation-measurement systems are compared as

to dynamic range and typical accuracy.

Fixed- Frequency

Measurement

of

Small Attenuation

(<

5

dB)

Dual-channel audio substitution (Fig. 8)

Accuracy:

0.01

dB

SYSTEM

DUAL CHANNEL

AUDIO FREQUENCY

SINGLE CHANNEL

AUDIO FREQUEhCY

AUDIO

DIRECT RATIO

"

''j,;,,',',',

'

,'

'j,

lPAR.4LLEL

If.

92YSTI

rL

TIOh

1

L

3

I

1

I I

I

0

IO

20

30

40

50

60

70

80

90

100

ATTENUATION IN

DECIBELS

Fig.

7.

Comparison

of

most commonly used attenuation measurement systems.

11-6

REFERENCE

DATA

FOR ENGINEERS

TABLE

3.

RESISTANCE VALUES

AND

ATENUATION

FOR

MINIMUM-LOSS L

PAD*

Measurement

of

Moderate Attenuation

(1

to

30

dB)

Audio substitution

R

I

IR2

j

k

dB

20.0

19.49

1.026 18.92

16.0

15.49

1.033 17.92

12.0

1

1.49

1.044 16.63

10.0

9.486

1.054 15.79

8.0 7.484

1.069 14.77

6.0 5.478

1.095 13.42

5.0

4.472

1.118 12.54

4.0 3.469

1.155 11.44

3.0

2.449

1.225 9.96

2.4 1.833

1.310 8.73

2.0

1.414

1.414 7.66

1.6 0.9798

1.633 6.19

1.2

0.4898

2.449 3.77

1

.o

0

m

0

*

For

R2

=

1

ohm and

Rl

>

R2.

If

R2

#

1

ohm, multiply

values by

R2.

For

ratios

not in the table, use the formulas in

the text.

Examples

of

use

of

table:

If

RI

=

50

ohms and

R2

=

25

ohms, then

Rl/R2

=

2.0,

and

If

R,/R2

=

1.0,

minimum loss

=

0

dB.

j

=

k

=

1.414

x

25

ohms

=

35.35

ohms.

For

RI/R2

=

2.0,

the insertion

loss

with the use of

j

and

k

for matching is

7.66

dB above that

for

R,/R2

=

1.0.

Advantage: Single radio-frequency source

Attenuation standards: Audio attenuator

(resistive)

Ratio transformer

(inductive)

(A) Single channel (Fig.

9)

Accuracy: 0.1 dB

(B) Dual channel (Fig.

8)

Accuracy:

0.05

dB

The major advantage

of

systems (A) and

(B)

is sim-

plicity.

Measurement

of

High

Attenuation

(30

to

>

100

dB)

Intermediate-frequency substitution

(A) Series substitution (Fig. 10)

Accuracy: 0.1

to

1 or

2

dB

Disadvantage: Minimum

loss

of standard

attenuator (typically

30

dB for a

waveguide-below-cutoff attenuator) in series

with the mixer reduces dynamic range.

Accuracy: 0.1 to 1 or

2

dB

Advantage: Minimum

loss

of standard

intermediate-frequency attenuator does not

affect system sensitivity; gain stability of

intermediate-frequency amplifier does not

influence accuracy.

Disadvantage: More complex

(B)

Parallel substitution (Fig. 11)

All intermediate-frequency systems have an inherent

limitation due to the range of power conversion linearity

of

the mixer. Beyond

90

dB, corrections may have to be

made for linearity deviation. Partial radio-frequency

substitution is often used to extend range, but mismatch

and leakage errors

are

prevalent.

Fig.

8.

Dual-channel audio substitution system (Reference

1).

11-7

0.005 76

0.0173

0.0288

TABLE

4.

POWER

DISSIPATION WITHIN

TEE

PAD*

0.01 12 0.005 625

0.0334 0.016 113

0.0543 0.025 643

'OUT

R"

-

0.0403

0.0518

0.0575

dB

0.0743 0.034 279

0.0933 0.0421

0.1023 0.0456

Watts

Input

Series

Resistor

0.126

0.137

0.149

0.160

0.170 998

Watts

Shunt

Resistor

0.120

0.1368

0.1525

0.1672

0.1808

0.1953

0.2075

0.2205

0.232

0.242 114

Watts

Series

Resistor

output

0.598

0.667

0.726 386

0.1

0.3

0.5

0.3005 0.0377

0.266 0.0266

0.230 36 0.018 2460

0.7

0.9

1

.o

0.776

0.818

0.938

0.980

1.2

1.4

1.6

1.8

2.0

0.1955 0.0123

0.1635 0.0100

0.0593 0.0010

0.0196 0.0001

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

5

6

7

8

9

10

12

14

16

18

20

30

40

0.0690

0.0804

0.0918

0.103

0.114

0.0523

0.0582

0.0635

0.0679

0.0718

0.0758

0.0787

0.0818

0.0839

0.085 698

0.182

0.193

0.204

0.215

0.226

0.2515

0.2605

0.2695

0.2775

0.285

0.0870

0.0882

0.0890

0.0897

0.0898

0.280

0.332

0.382

0.430

0.476 218

0.519

0.3145

0.332

0.341

0.343

0.337 94

0.328

0.0884

0.0833

0.0761

0.0681

0.059 9527

0.519

*For 1-watt input and matched termination.

If

input

#

1

watt, multiply values by

pi,.

Measurement

of

Attenuation Above

1

dB

Broad band

Measurement

of

Small

Attenuation (Less

Than

5

dB)

Single- or dual-channel audio (Figs.

8

and

9)

Accuracy:

0.01

to

0.05

dB

Advantage: Single radio-frequency source

Dual-channel audio substitution (Fig.

8)

Accuracy:

0.01

dB

11-8

I

RF

SOURCE

7

1

,I

REFERENCE

DATA

FOR ENGINEERS

I

r

TEST

I

SQUARE-LAW AUDIO FREQ AMPLITUDE

I

ATTENUATOR INDICATOR

STANDARD

-

DETECTOR

&

ATTENUATOR

7

DETECTOR

-

I

TABLE

5.

LIST

OF

POPULAR COAXIAL CONNECTORS

I,

Connector Contact

Type TYP Specifications

N

Female Mil-C-39012/2

N Male Mil-C-390 12/

1

C Male

Mil-C-390 12/6

C Female Mil-C-3901217

sc

Male Mil-C-39012/39

Mil-C-390 12/36

sc

Female

TNC

Male Mil-C-39012/26

TNC

Female Mil-C-390 12/27

BNC Male Mil-C-39012/16

BNC Female Mil-C-39012117

SMA Male Mil-C-39012/55

SMA Female Mil-C-39012/57

7-mm GPC

Waveguide Choke or cover flange Mil-F-3922

Sexless

IEEE

Std. 287-1968

14-rnm GPC Sexless

IEEE

Std. 287-1968

I

References-Mil-C-39012 on Coaxial Connectors; Mil-F-3922 on Waveguide Flanges, General Purpose;

IEEE

Std. 287- 1968

on Precision Coaxial Connectors

SOURCE

I

RF

1

INSERTION PLANES

'

//

\j

AUDlOFREQ AMPLITUDE

I

K

ATTENUATOR STANDARD DETECTOR

&

DETECTOR

TEST SQUARE-LAW

H

2"

7

AUDIO

MODULATION

Fig. 9. Single-channel audio substitution system (Reference 1).

OPTlONAl

MODULATION OSCILLATOR

LEVEL

INDICATOR

SECOND

IF

DETECTOR&

-

AMPLIFIER

-

MIXER

-

STANDARD

-

SOURCE

ATTENUATOR

'

AMPLIFIER

4

MATCHING MATCHING

INSERTIOh

I

1

POINT

Z,,--

'

Noise

njection can

he

used

to

exirnd

range

Fig.

10.

Series type intermediate-frequency substitution system (References 3 and

4).

ATTENUATORS

11-9

INSERTION

MATCHING BALANCE

(FOR CW ONLY)

MATCHING

I-

Z"

I

SQUARE WAVE

100%

MODULATION

RF

'

AUDIO

SOURCE MODULATION

-

SOU ARE WAVE

\

l00o

MODU,LATION

I

.

IF

I

SOURCE

I

\

180°

OUT-OF-PHASE

(SQUARE WAVE MODULATION)

-.----

REFERENCE

1

IF

OSCILLATOR AMPLIFIER

&

2ND DETECTOR

/

NORMALLY BRIDGED

SAMPLING

EXCEPT FOR CW

SWITCH

(FOR CW

ONLY) COHERENT

DETECTOR

AMPLIFIER

&

INDICATOR

IF

ATTENUATOR

-

STANDARD

FROM AUDIO

f

MODULATION

Fig.

11.

Parallel IF substitution system with noise injection and coherent detection (References

5

and

6).

Disadvantage: Limited dynamic range (about

30

dB) without partial radio-frequency substitution

The major difficulty in broadband techniques is

maintaining a Z,-matched source and terminating im-

pedance. The increased mismatch uncertainty due to

impedance variations

of

source and load with frequency

may degrade the above accuracy figures by an order

of

magnitude. A technique producing an equivalent Z,-

matched source impedance is discussed in Reference

9.

Swept

or

Stepped

in

Frequency

Measurement

of

Attenuation Less than

30

dB

(1) Audio-substitution dual channel (Fig.

8

with

addition

of

level-stabilized swept radio-

frequency source)

Accuracy:

0.05

to

0.1

dB

Advantage: Potentially most accurate system

Disadvantage: Impedance variation

Audio ratio technique (Fig.

12)

Accuracy:

0.1

to

0.3

dB

Advantage: Rapid measurement, simplicity

Disadvantage: Curvilinear reference lines

which can be straightened through the use

of

memory circuits

(2)

(3)

Sampling (Fig.

13)

Accuracy:

0.1

to

0.5

dB dependent on

uncertainty of system precalibration

MODULATION

6

TRANSMISSION LOSS

=

KF

SWEEP

DISPLAY OR

SWEEP

OSCILLATOR

MEASUREMENT

II-LJ

REFERENCE TRANSMISSION

DIRECTIONAL

COUPLER COUPLER

INSERTION

POINT

Fig.

12.

Diagram

of

broadband direct-ratio system (Refer-

ences

2

and

9).

11-10

REFERENCE

DATA

FOR

ENGINEERS

TEST

CHANNEL

REFERENCE

PHASE

SHIFTER

Fig.

13.

Sampling conversion method

of

attenuation measurement (Reference

8).

Advantages: (A) Digital technique permits

use of logic circuitry

for

automatic correction

of

measurement errors

measurement technique

(B) Extremely rapid

Disadvantage: Very complex

Measurement

of

Attenuation Greater than

30

dB

Sampling (Fig. 13)

Accuracy: 0.5-2 dB to

50

or

60

dB dependent on

uncertainty of system precalibration

Advantages: (A) Digital technique permits

use of logic circuitry for

automatic correction of

measurement errors

(B) Extremely rapid

measurement technique

Disadvantage: Very complex

The aforementioned measurement techniques are not

intended to

be

all-inclusive. These are representative

of

current practices only. No mention has been made of

specialized power ratio, modulated subcarrier, radio-

frequency substitution, homodyne, impedance, or self-

calibrating methods,

or

range extension by using a

supervised change of incident power level.

REFERENCES ON

ATTENUATION

MEASUREMENT

1. Sorger, G.

U.,

and Weinschel, B.

O.,

“Comparison

of Deviations from Square Law for RF Crystal

Diodes and Barretters,”

IRE Transactions

on

Instru-

mentation,

Vol.

1-8,

Dec. 1959, pp. 103-1 11.

2.

Weinschel,

B.

O.,

“Measurement of Microwave

Parameters by the Ratio Method,”

Microwave

Jour-

nal,

Aug. 1969, pp. 69-73.

3.

Terman,

F.

E.,

“Linear Detection

of

Heterodyne

Signals,”

Electronics,

Nov. 1930, pp. 386-387.

4. Harnett, D.

E.,

and Case,

N.

P., “The Design and

Testing of Multi-Range Receivers,”

Proceedings

of

the IRE,

Vol. 23, June 1935,

pp.

578-593.

5. Gainsborough, G. F., “A Method of Calibrating

Standard Signal Generators and Radio Frequency

Attenuators,”

Journal

of

the IEE,

Vol. 94, Pt.

111,

May 1947, pp. 203-210.

6.

Weinschel, B.

O.,

Sorger, G.

U.,

and Hedrich,

A.

L.,

“Relative Voltmeter

for

VHF/UHF Signal

Generator Attenuator Calibration,”

IRE Transac-

tions

on

Instrumentation,

Vol.

1-8,

Mar. 1959, pp.

7. Schafer, G.

E.,

and Rumfelt, A.

Y.,

“Mismatch

Errors

in Cascade-Connected Variable Attenu-

ators,”

IRE Transactions

on

Microwave Theory

and

Techniques,

Vol. MTT-7, Oct. 1959, pp. 447-453.

22-3 1.

ATTENUATORS

11-11

8. Adam,

S.

F.,

“A New Precision Automatic Micro-

wave Measurement System,”

IEEE

Transactions on

Instrumentation and Measurement,

Vol.

IM- 17,

Dec. 1968, pp. 308-313.

9.

Engen,

G.

F.,

“Amplitude Stabilization

of

a Micro-

wave Signal Source,”

IRE

Transactions

on

Micro-

wave Theory and Techniques,

Vol.

MTT-6, Apr.

1958, pp. 202-206.

OTHER GENERAL

REFERENCES

1.

MIL-A-3933, General Specification for Fixed

Attenuators.

2. Section 14A on Attenuators

of

MIL-HDBK-216

on RF Transmission Lines and Fittings.

References

1

and

2

can be obtained through:

Commanding Officer

Naval Publications and Forms Center

5801

Tabor Avenue

Philadelphia, PA 19120

3. IEEE STD-474- 1973, Specifications and Test

Methods

for

Fixed and Variable Attenuators, DC

to 40 GHz.

4. IEEE STD-100-1977, Dictionary of Electrical

&

Electronics Terms

References 3 and 4 can be obtained through:

IEEE Service Center

445 Hoes Lane

Piscataway,

NJ

08854

12

Measurements and

Analysis

Arthur

Fong,

Robert Coackley, John

J.

Dupre, Stephen

J.

Greer,

Siedried Linkwitz,

John

R.

Page,

Ronald

E.

Pratt,

Douglas

K.

Rytting, and Gary

D.

Sasaki

Impedance Bridges

12-3

Fundamental Alternating-Current or Wheatstone Bridge

Wagner Ground Connection

Capacitor Balance

Series-Resistance-Capacitance Bridge

Wien Bridge

Owen Bridge

Resonance Bridge

Maxwell Bridge

Hay Bridge

Schering Bridge

Substitution Method for High Impedances

Measurement With Capacitor in Series With Unknown

Measurement

of

Direct Capacitance

Felici Mutual-Inductance Balance

Mutual-Inductance Capacitance Balance

Hybrid-Coil Method

Q

of

Resonant Circuit by Bandwidth

Q

Meter (Hewlett-Packard 4342A)

Twin-T Admittance-Measuring Circuit (General Radio Type

Ratio-Arm Bridges (Wayne Kerr)

Automatic Impedance Meters

82

1

-A)

12-1

Middleton W.M. (ed.) Reference Data for Engineers: Radio, Electronics, Computer and Communications

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