NATL INST. OF STAND & TECH R.I.C.

I 111 mi MM llll II A111DS Sm2D3

NJST

PUBLICATIONS

NisrUnited States Department of Commerce

Technology Administration

National Institute of Standards and Technology

NIST Technical Note 1507

Uncertainty Assessment for Standard

Antenna Measurements on the

Open Area Test Site

Dennis G. Camell

NIST Technical Note 1507

Uncertainty Assessment for Standard Antenna

Measurements on the Open Area Test Site

Dennis G. Camell

Radio-Frequency Division

Electronics and Electrical Engineering Laboratory

National Institute of Standards and Technology

325 Broadway

Boulder, Colorado 80303-3328

September 1998

^TES °*

U.S. DEPARTMENT OF COMMERCE, William M. Daley, Secretary

TECHNOLOGY ADMINISTRATION, Gary R. Bachula, Acting Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Raymond G. Kammer, Director
National Institute of Standards and Technology Technical Note

Natl. Inst. Stand. Technol., Tech. Note 1507, 20 pages (September 1998)

CODEN:NTNOEF

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1998

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Contents

1. Background of OATS Measurements at NIST 1

2. Description of the Standard Antenna Method 1

3. Explanation of Test Setups and Measurement Equipment 2

4. Assessment of Uncertainties 3

4.1. rf-to-dc Transfer Function of the Standard Antenna 5

4.2. Effective Length of the Standard Antenna 7

4.3. dc Voltage Measurement of the Standard Antenna 8

4.4. rf Voltage Measurement of the AUT 8

4.5. Measurement of Loss in the Receiving Cable 10

4.6. rf Source Stability 10

4.7. Alignment of Antennas on OATS 11

4.8. E-field Uniformity 11

4.9. Measurement Repeatability and E-field Environmental Interaction 12

5. Summary of Uncertainties 12

6. Conclusions 14

7. References 14

in

Uncertainty Assessment

for Standard Antenna Measurements

on the Open Area Test Site

Dennis G. Camell

Radio-Frequency Fields Group

Radio-Frequency Technology Division

National Institute of Standards and Technology

Boulder, CO 80303

The National Institute of Standards and Technology calibrates electromagnetic

compatibility antennas using the standard antenna method. This method uses a standard

antenna to precisely measure the electric field at a location. An antenna under test is placed where the standard antenna was located to determine its antenna factor.

Complete uncertainties are determined for calibrations performed on the open-area-testsite leading to a statement of uncertainty of the method. The results of this procedure

yield a standard uncertainty of 0.4 dB. Assessment of this uncertainty statement and its details are presented in this paper.

Keywords: uncertainty analysis, open area test site, electromagnetic compatibility,

measurement, standard antenna, antenna factor.

1. Background of OATS Measurements at NIST

The National Institute of Standards and Technology (NIST) calibrates antennas for testing of

electromagnetic compatibility (EMC). NIST uses the standard antenna method (SAM) to determine antenna

factor in reference [1]. This method relies on a fundamental antenna (a half-wave dipole) and a simplified

converter (a diode) whose determination of a linearly polarized continuous-wave, electric field (CW E-field)

is easily calculable. This method also is independent of the condition of the ground plane since it measures

the E-field at the test location. This allows for repeatable measurements of the E-field on the open area test

site. Only steady-state, continuous-wave rf fields with sinusoidal time variation are measured.

2. Description of the Standard Antenna Method

The standard antenna method uses a set of half-wave (k/2) dipoles designed and built at NIST. The

standard antennas are self-resonant, half-wave dipoles with a high-impedance Shottky diode across the

center gap and cover the frequency range of 30 MHz to 1000 MHz in incremental steps. Currently, the

available measurement frequencies are 30 MHz to 100 MHz every 10 MHz, 100 MHz to 300 MHz every

25 MHz, 300 MHz to 600 MHz every 50 MHz, and 600 MHz to 1000 MHz every 100 MHz.

Briefly, the SAM uses a standard antenna to measure the E-field at a location. Then the antenna under test (AUT) replaces the standard antenna and its response to that E-field is measured. An rf-to-dc voltage

transfer function is determined before each test to characterize the response of the standard antenna to if

signals. The E-field is calculated from the standard antenna's dc response, the voltage transfer function, and

its physical and electrical characteristics. The antenna factor of the AUT is a ratio of the measured E-field to

1
the AUT's response. Details of the NIST standard antenna and this method for measuring the magnitude of

an E-field are in reference [1].

The primary equations for determining the antenna factor for an AUT using the standard antenna method

are: E = VJL<,

oc dc KdB =EdB -(Vc + CLdB +SAdB )

(la)

(lb)

(lc)

where

E = electric field strength, V/m,

Voc = open circuit rf voltage of NIST standard antenna, V,

M= linear fit coefficient (slope),

B = linear fit coefficient (Y intercept point), V,

Vdc - dc voltage response of NIST standard antenna, V,

Leff= effective length of the NIST standard antenna, m,

KdB = antenna factor of antenna under test, dB/m,

EdB =(20*log(£)), electric field strength, dB (re IV) /m,

VdB = response of antenna-under-test from the electric field, dB (re IV),

CLdB - insertion loss of the cable, dB, and

SAdB = correction factor for the receiver, dB.

3. Explanation of Test Setups and Measurement Equipment

The SAM consists of two parts, (1) the determination of the rf-to-dc voltage transfer function of the

standard antenna performed inside the laboratory, and (2) the measurement of the E-field and the AUT's

response on the OATS.

Figure 1 shows the first measurement setup as a block diagram. The rfsource consists of a rf signal

generator, a low power (5 W) amplifier, and a low-pass filter. The rfpower monitor is a calibrated dualdirectional coupler, calibrated coaxial cables, and calibrated power sensors and meter. The 180°hybrid and

pair of customized coaxial t-connectors with 50 Q loads provide a controlled rf signal to the standard

antenna's feed point. The dc voltage output from the standard antenna mount is measured by the dc

voltmeter with a 100 MQ load across its input.

RF

SOURCE

RF POWER

MONITOR

180°

HYBRID &

T connectors

STD

ANTENNA

MOUNT

DC

VOLT

METER

Figure 1. Block diagram of the setup to measure the rf-to-dc voltage transfer function for the

NIST standard antenna mounts.
RF

SOURCE t

RF POWER

MONITOR k. COAX TRANSMITTNG

w w Ca±$lijnlt r ANTENNA

STANDARD

ANTENNA —

HIGH-Z

LOAD k. DC

• VOLTMETER —

E field over GROUND

SCREEN

P

; ik ANTENNA

UNDER TEST —

COAX

k RF

CABLING P• RECEIVER

Figure 2. Block diagram of the Standard Antenna Measurement on the OATS.

The second part of the SAM is a measurement of the E-field and the AUT's response. This is a two-step

sequential process. As figure 2 shows, this sequence involves a change on the receiving side of the setup.

The rfsource and rfpower monitor blocks are as described earlier, but with a larger rf amplifier (80 W)

with the source. The transmitting antenna is either a tuned dipole (30 MHz -125 MHz) or a log-periodic

antenna (125 MHz -1000 MHz) mounted on a height adjustable tripod. The E-fieId over ground screen

symbolizes the interaction of the transmitted field with the environment of the OATS. This interaction

includes intrusive ambient signals, reflections off nearby objects (including the test equipment), and

reflections off the ground plane. The blocks for standard antenna and antenna under test represent the

antennas used in the test. The high-Z load is a 100 Mfi load that is placed across the dc voltmeter 's input to regulate the signal from the standard antenna. The rfreceiver is a calibrated spectrum analyzer configured

to predetermined settings. All of the equipment, except for the antennas and cables, reside below the 30 m

by 60 m ground plane in an underground room.

4. Assessment of Uncertainties

Even though reference [1] details the standard antenna method at NIST, the description of the uncertainties

of the measurement is cursory when compared to present requirements. With the current emphasis on

statement of uncertainties in EMC antenna measurements around the globe, a further look at uncertainties

of the SAM is merited. Reference [2] is a NIST document that provides guidelines for uncertainty analysis.

Several other publications listed as references [3 to 5] offer procedures for EMC antenna measurements that

range from general guidelines to specific steps. This study agrees with and will follow those procedures.

Also, in agreement with these publications, uncertainties will be expressed in decibels.

The individual uncertainties ufej) in the Standard Antenna Method will be examined using the previous

equations (la to lc) and the block diagrams (figures 1 and 2). The following are identified as sources of

uncertainty:

(1) rf-to-dc transfer function of the standard antenna, Urf.dc (2) effective length of the standard antenna, Uuff

(3) dc voltage measurement of the standard antenna, UdC (4) rf voltage measurement of the AUT, Urf (5) measurement of loss in the receiving cable, uCbi (6) rf source stability, usource
(7) alignment of antennas on OATS, uaiig„ (8) E-field uniformity, uUfm

(9) measurement repeatability and E-field environmental interaction, urept

Each of these terms will be looked at to determine its influence on the combined standard uncertainty.

Terms that are based on measured data will be plotted as data in a graph. The measured terms will also be

presented in a graph as a histogram of the data. A histogram is a graphical representation of the number of

measurement values that fall in a sequence of "bins" which partition the continuous range of measurement

values. This tool provides information based on the number of occurrences of a value in a data set when

repeated measurements are made. That is, it presents a distribution of the data showing the spread and

shape of the measured data. For example, for data from dB to 0.25 dB (the range of data), the histogram

would show the number of data for each 0.05 dB range (the bins) and the cumulative percentage of data as the bins increased from dB to 0.25 dB in steps of 0.05 dB.

We can apply a general formula for propagation of independent uncertainties from reference [2] to obtain

the combined standard uncertainty. This equation can also be used if any individual uncertainty has more

than one term of influence. For a general linear function, the combined standard uncertainty is

Incorporating the terms from the above uncertainty list and using eq (2),

«. =>„-* y + Kr y+ky -k«„ )

2 huo, y +o<_

)

2 ««u.

)

2 h«+ y ^Z y . (3)

We inspect each individual term in sections 4.1 to 4.9 to determine its effect on the combined standard

uncertainty.

Instrument calibrations influence several uncertainty terms in this test. These components are included

where appropriate. All of the instrumentation used in the SAM measurements are traceable to NIST

standards, either calibrated by the manufacturer or through internal measurements. Instruments used in

SAM are a power meter and sensor, an rf spectrum analyzer, a dc voltmeter, and a signal generator.

The Radio-Frequency Fields Group at NIST has a calibrated NIST type-IV power meter as described in

reference [6] with a thermocouple sensor that is calibrated at NIST. The worst-case uncertainty

specification on the power sensor calibration is 0.5 percent from reference [7]. This power sensor and

type-IV power meter combination is used to calibrate the power meter and sensors and the spectrum

analyzer used in the measurement.

The amplified signal source depends upon the combined signal generator and the amplifier output. The

power output of the signal generator is a relative value for the SAM and therefore only the resolution of the

device is pertinent. The manufacturer-rated resolution for the output power is 0.1 dB from reference [8].
Table 1. List of standard uncertainty for instrumentation of the SAM measurement.

Instrumentation Uncertainty (dB) Cal. Reference

signal generator 0.1 Mfr.

power meter/sensors 0.089 Internal

dc voltmeter <0.001 Mfr.

spectrum analyzer 0.123 Internal

The power meter and sensors were compared to the calibrated type-IV power meter. The 2 percent

repeatability of the power sensor measurements is combined with the 0.5 percent of the type-IV calibration

by using eq (2). This gives a standard uncertainty of 10-log(l + ^/(0.02)

2 +(0.005)2 ) = 0.089 dB for the

power meter and sensors.

According to the manufacturer in reference [9], the standard uncertainty of the DVM for dc voltage

measurements is < 0.01 percent. This converts to <0.001 dB.

The spectrum analyzer was also compared to the type-IV power meter and calibrated power sensor. Its average repeatability was 0.121 dB (see section 4.5) giving a standard uncertainty in these measurements of

^(0.1 2 1)

2 + (10-log(1.005))2 = 0.123 dB.

The standard uncertainties due to instrumentation calibrations are summarized in table 1

.

4. 1. rf-to-dc Transfer Function ofthe Standard Antenna

An rf-to-dc voltage transfer measurement (figure 1) is made for each measurement run on the OATS and

has an associated uncertainty Urf.dC. A study of the measurement will help determine its uncertainty.

Since the response of the Shottky diode depends upon temperature, the voltage transfer function is measured at temperatures within 10 °C of the external environment. This range caused negligible differences

in the results.

Data are taken for dc voltages from 0.05 V to 2.5 V using the setup in figure 1 . A linear fit is obtained for

each set of data and this curve is then used to determine the open-circuit voltage from eq (lb). The

correlation coefficient for the curve fit (r in reference [2, p. 180]) is greater than 0.995. The set of curves

for each standard mount is analyzed for the maximum variation from curve to curve. Figure 3 shows a summary of the average and standard deviation of this variation expressed in decibels.

A histogram of these data is given in figure 4 using bins every 0.005 dB. The histogram shows that there is an offset in the data around 0.04 dB and that most of the data have little variation. For dc voltages between

0.25 V and 1.50 V, which are typical values used for SAM testing, the average variation is 0.047 ± 0.012 dB.

Associated with this measurement, from figure 1, are thermocouple power meter/sensors that have listed

uncertainties of 0.089 dB, as reported in section 4.1. The other items from figure 1, losses of the directional
\J.J -] T

0.25- I

1

Itage

variation,

dB

o en

k>

1

l\

r

i

i VI

i

1

I § 0.1 -

—i—

I

—h1

—t—

i

—tT

J.

—tT T

0.05 -

1

1 1 1 1 1 1

- —

1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.25 0.5 0.75 dc voltage, V

1.25 1.5

Figure 3. Variation due to data curve fit, rf-to-dc voltage transfer measurement.

25

20 -

« 15 3

O

o

CD !Q

'"""!" Bin Count D Cumulative %

o l a i D i D i a i n i o i ca i l^ i

Bin, dB

Figure 4. Histogram of average variation due to data fit, rf-to-dc voltage transfer

measurement.
coupler and losses in the hybrid were also measured with a power meter/sensor having uncertainties of

0.089 dB, for each component. Combining these values as eq (2) suggests gives = ^(0.047)

2 +(0.089)

2 +2-(0.089)2 u =0.161dB. RF-DC

4. 2. Effective Length ofthe Standard Antenna

Determination of the effective length of the NIST standard antenna Leff was recently addressed in reference

[10]. Estimates of the change in the computed values of the effective length dZ^were detailed for various

setup configurations. The uncertainty for this term is defined as uLeff = 10*log(l + dLeff /Leff )

.

Figure 5 shows a summary of this uncertainty analysis that is reduced to an average value of

ULeff = 0.019 ± 0.01 1 dB. The histogram for this data is shown in figure 6 with bins every 0.001 dB. The

histogram shows a bimodal shape where each peak is due to different setups of the antennas as detailed in

reference [10]. Otherwise this graph shows a normal distribution of the data.

0.12

100 Frequency, MHz

1000

Figure 5. Average uncertainty ofZ,e^vs. frequency.
16

14 imrnt Bin Count —B—Cumulative %

oaaDJDDDpaQQ^?

I M I I I I I LJ. "I—I—H^H-H[

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

00%

h- o> i-

(n r>j co o o o

co in r»- o)

CO CO CO CO o o o o ootid

2!o5

Bin, dB

Figure 6. Histogram ofZ-^ uncertainties.

4.3. dc Voltage Measurement ofthe Standard Antenna

DC voltage measurements are the best controlled of any during an EMC measurement. From table 1, for dc

voltage measurements, the uncertainty of the DVM is O.001 dB. This value is below the round-off for the

uncertainty of this test. As expected, this is a very small value and will be considered negligible.

4. 4. rf Voltage Measurement ofthe A UT

The response of the AUT is measured with a spectrum analyzer. The spectrum analyzer is compared to a

calibrated power sensor and meter for each reference level used. Reference levels for the spectrum analyzer

varied from +5 dB (re 1 mW) to -20 dB (re 1 mW) every 5 dB (re 1 mW). This comparison is performed

for every AUT.

Figure 7 shows the repeatability of these comparison measurements. Figure 8 is the histogram using

0.01 dB bins. The average repeatability is 0.121 ± 0.035 dB. This shape is also normal with some data

trailing at the high end.

The power sensor and meter has an instrumentation uncertainty of 0.089 dB from table 1. Combining these

values as eq (2) suggests gives u^ = V(0.121)

2 +(0.089)

2 = 0.150dB.
0.25

0.20

00i

2

0.15 -

0.10

0.05

0.00 100 200 300 400 500 600 700 800

Frequency, MHz

900 1000

Figure 7. Repeatability of spectrum analyzer measurements over frequency.

i&mai Bin Count —B—Cumulative %

u u u-1

1,1,1,1,1,1,1 ) 1 H

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

00%

Figure 8. Histogram of spectrum analyzer repeatability.
4. 5. Measurement ofLoss in the Receiving Cable

The loss of the coaxial receiving cable was measured with a power meter and sensor, over the frequency of

interest. The repeatability of these measurements is shown in figure 9. Figure 10 has the histogram for this

data using bins of 0.005 dB. The average repeatability is 0.029 ± 0.019 dB. There are fewer data here than

for the other terms; however, there is enough to determine the average value for this passive device.

This part of the uncertainty has two components, the repeatability of the measurement and the calibration of

the equipment. The total uncertainty of this measurement, including the instrument calibrations from table 1,

is uM = V(0.029)

2 +(0.089)2 = 0.094 dB.

4. 6. rfSource Stability

The rf source for SAM consists of a signal generator, an 80 W rf power amplifier, and a low-pass filter. The

signal generator by itself has a very stable and repeatable rf output. However, the rf amplifier's output is dependent upon its warm-up time and the amount of drive into the unit. For this type of measurement, the

amplifier is allowed to stabilize over 20 min and the input drive is only on long enough to take a steady

reading. A reading is considered steady when the rf power monitor's reading is stable for a few seconds.

Since the drift in the amplifier can be compensated with the output of the signal generator, this leaves only

the resolution of the signal generator as a component for uncertainty. Therefore, from table 1, the

uncertainty due to this component is usource = 0. 1 dB.

0.14

100 200 300 400 500 600 Frequency, MHz

700 800 900 1000

Figure 9. Repeatability of cable loss measurement.

10
D D D D D O

^5" D D D D D b-b-B-*3 D D D ° D

n : wwn Bin Count —B—Cumulative %

|LJ|tU|EJ |LJ| 1 1 1 1 ,_ H 1 1 h H 1 (- in in in in in s a 8 o s

o o o o o

Bin

8 IP

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

00%

o5

Figure 10. Histogram of cable loss repeatability.

4. 7. Alignment ofAntennas on OATS

The transmitting and receiving antennas are placed on tripods or on an EMC mast for measurement on the

OATS. Position alignment includes the setting of height for each antenna and the spacing between antennas

as well as the orientation of each antenna. Tripods are stationary and are used for fixed positions. The

position and orientation of an antenna on a tripod is repeatable within 1 cm in each direction (height and

separation distance). The EMC mast is a motor-controlled pulley system that is also repeatable within 1 cm

in each direction. These positioning variations project changes in the E-field of uang

„ = 0.08 dB for two

dipole antennas with typical separation distance of 10 m and antenna heights of 2 m.

4.8. E-field Uniformity

The characteristics of both receiving and transmitting antennas affect the formation of the E-field and are

directly relevant to the combined standard uncertainty. Included in this term is each antenna's directivity, its height above the ground plane, radiation pattern and physical size. The directivity of the AUT will be

dependent in part upon its environment; this term will be included in the resultant antenna factor. An

increase in the alignment uncertainty due to variations in the directivity is estimated to be 0. 1 dB. The

radiation pattern is of concern when it differs from the standard dipole pattern, since the standard dipole is the reference object. Estimated uncertainties on the order of 0.15 dB can be expected. The size of the

antenna dictates the spatial volume used for measurement of the E-field. So, a larger antenna requires an

E-field that is uniform over a larger volume than is required for a small antenna. This adds another 0. 15 dB

of uncertainty due to the expected uniformity of the E-field over different volumes for typical EMI antennas. Combining these as described earlier, eq (2) gives u

ufm = 7(0.10)

2 + (0.15)2 + (0.15)2 = 0.235 dB.

11
4. 9. Measurement Repeatability and E-Jield Environmental Interaction

This is the most difficult value to assess. It depends on the interaction of the transmitted E-field with the

environment of the OATS; including intrusive time-varying ambient signals, reflection from nearby objects,

and non-ideal reflection off the ground plane. All this is further dependent upon the frequency of interest.

Ambient signals can be viewed only when the measurement signal is off. Use of narrow-band filters allows

the rf receiver to bypass most intrusive signals. The diode detector on the standard antenna's response

allows for a broadband response to be measured with the dc voltmeter.

At NIST, ambient signals are required to be less than or equal to 10 percent of the test signal, as measured

with the standard antenna. Higher signal strength from the source allows for the ambient signal to be

overwhelmed by the test signal. Sometimes, even this is not effective for large ambient signals on certain

days and requires a change in the orientation of the setup to minimize the intrusive E-field. This extreme measure is necessary only at a few frequencies and is rarely needed. It is however, very effective to

minimize the ambient signal, if directional.

Repeatability of measurements and use of check standard comparisons are standard components of SAM

tests at NIST. AUTs are measured at least two independent times and the results compared. The check

standard antennas are a set of broadband dipoles that are measured with every AUT. Results are compared

to historical data to ensure continuity at the site.

Even though this repeatability incorporates some of the other components stated earlier, this should signify

the uncertainty of the repeatability of the antenna under test and the condition of the OATS environment at

its worst case. Repeatability of SAM tests at NIST is <0.25 dB for any one AUT. Check standard antenna

repeatability is also <0.25 dB, based on its historical data. If we assume rectangular distribution for this

repeatability, this relates to a standard uncertainty of u , = 0.25 / V3 = 0. 144 dB.

5. Summary of Uncertainties

The individual standard uncertainties for this method are detailed in section 4 and summarized in table 2. This method employs a series of independent steps to arrive at the final outcome, the antenna factor of the

AUT. Uncertainties are classified into two types: A and B from reference [2]. For type A uncertainties, each

u(x,) is based on statistical data derived from previous measurements. For type B uncertainties, the u(x,) were determined from manufacturer's specifications or from engineering knowledge and experience. The

combined standard uncertainty uc is the root-sum-of-squares of each of these independent steps, as defined

in eq (2).

To summarize the individual uncertainty components:

• The open-circuit voltage from a linear curve fit where the slope is known to within 0.5 percent.

• The standard antenna lengths are measured to within 0. 1 percent.

• The dc voltage is considered exact. • The receiver and cable uncertainties are based on repeated measurements using calibrated equipment.

• The rf source is allowed to stabilize. • Antenna alignment is done with utmost care and precision, and a good tape measure.

12
• Repeat measurements assure any anomaly due to OATS interaction are discovered.

• Check standard antennas insure good repeat measurements.

The combined standard uncertainty for the SAM is obtained by using eq (2). Combining all the terms in table 2 gives uc = V(0.161)

2 +(0.019)

2 +(0.150)2 +(0.094)2 +(0.10)2 +(0.08)2 +(0.235)2 +(0.144)2 dB (4)

uc = 0.4 dB.

To obtain the expanded uncertainty U, we use a coverage factor as described in reference [2] of k = 2

giving U = k-uc (5)

or t/=0.8dB.

Table 2. Standard antenna individual uncertainties.

Description Variable Type Value (dB)

rf-to-dc transfer function of

the standard antenna Urf-dc

effective length of the

standard antenna uLeff

dc voltage measurement

of the standard antenna w^

if voltage measurement

of the AUT Urf

measurement of loss

B

0.161

0.019

neg.

0.150

in the receiving cable Ucbl A 0.094

if source stability

^source B 0.10

alignment of antennas on OATS "align B 0.08

E-field uniformity

Uufm B 0.235

Measurement repeatability

and E-field environmental

interaction

Urept A 0.144

13
6. Conclusions

Most of the antenna calibration work for the EMC measurement industry at NIST has been with biconical,

log-periodic, and tuned-dipole antennas. The antenna factor at frequencies between 30 and 1000 MHz is measured using the standard antenna method, which includes an uncertainty analysis needed for meaningful

measurement results.

When uncertainties are assessed, the full sequence of measurements needs to be addressed and not just

individual segments. This paper accurately presents the uncertainties for SAM measurements on the OATS.

The largest individual uncertainty is in determining the antenna characteristics. This uncertainty will be

present for any type of measurement procedure. The next two largest individual uncertainties are with the

E-field transfer function of the standard antenna and the rf voltage measurement of the AUT. These three

terms need to be reduced for any substantial reduction in the expanded uncertainty. These three terms will

be further analyzed in future work.

Current guidelines for analysis of the uncertainty have been applied for determining antenna factor for an AUT at NIST. The results of this procedure yield an expanded uncertainty of 0.8 dB or a standard

uncertainty of 0.4 dB.

7. References

[1] Camell, D.G., Larsen, E.B., Cruz, J.E.; NBS calibration procedures for horizontal dipole antennas

(25 to 1000 MHz); Nat. Bur. Stand. (U.S.) Tech. Note 1309; April 1987.

[2] Taylor, B.N., Kuyatt, C.E.; Guidelines for evaluation and expressing the uncertainty of NIST

measurement results; Natl. Inst. Stand. Technol. Tech. Note 1297; 1994.

[3] Hill, D.A., Kanda, M.; Measurement uncertainty of radiated emissions; Natl. Inst. Stand. Technol. Tech.

Note 1389; March 1997.

[4] NAMAS Executive, Natl. Physical Lab. Teddington, Middlesex, England; The treatment of uncertainty

in EMC measurements; NIS 81, Edition 1; May 1994.

[5] Bronaugh, E.L., Osburn, J.D.; A process for the analysis of the physics of measurement and

determination of measurement uncertainty in EMC test procedures, IEEE Intl. EMC Symp.,

p. 245-249, Santa Clara CA; Aug. 19-23, 1996.

[6] Larsen, N.T.; A new self-balancing DC-substitution RF power meter; IEEE Trans. Instrum. Meas.,

IM-25(4): 343-347; Dec. 1976.

[7] Natl. Inst. Stand. Technol. Special Test Report; Coaxial Bolometer Unit; Natl. Inst. Stand. Technol.

Test No. 0010; May 1998.

[8] Hewlett Packard Operating Manual; HP 8642 A/B synthesized signal generator operating manual,

Vol. 1; Manual Part No. 08642-90013; Rev. 20 Mar 85.

14
[9] Hewlett Packard Service Manual; Model 3478A digital multimeter; Manual Part No. 03478-99008;

Sept. 1987.

[10] Kawalko S.F., Kanda M.; Effective length and input impedance of the NIST standard dipoles,

IEEE Trans. Electromagn. Compat. 39(4): 404-408; Nov. 1997.

15

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other special publications appropriate to this grouping such as wall charts, pocket cards, and

bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical

properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NIST under the authority of the National Standard Data Act (Public

Law 90-396). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published bi- monthly for NIST by the American Chemical Society (ACS) and the American Institute of Physics (AIP).

Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington,

DC 20056.

Building Science Series—Disseminates technical information developed at the Institute on building

materials, components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability

and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of

the subject area. Often serve as a vehicle for final reports of work performed at NIST under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce

in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized

requirements for products, and provide all concerned interests with a basis for common understanding of

the characteristics of the products. NIST administers this program in support of the efforts of privatesector standardizing organizations.

Consumer Information Series—Practical information, based on NIST research and experience, covering

areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order the above NIST publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402.

Order the following NIST publications—FIPS and NISTIRs—from the National Technical Information

Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the

official source of information in the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of

Title 15 CFR (Code of Federal Regulations).

NIST Interagency Reports (NISTIR)—A special series of interim or final reports on work performed by

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