1 1 fUnited States Department of Commerce

I 1

I Technology Administration

National Institute of Standards and Technology

NISTIR 3989

EMC STANDARDS AND REGULATIONS:

A BRIEF REVIEW

M.T. Ma

NISTIR 3989

EMC STANDARDS AND REGULATIONS:

A BRIEF REVIEW

M.T. Ma

Electromagnetic Fields Division

Electronics and Electrical Engineering Laboratory

Technology Administration

National Institute of Standards and Technology

Boulder, Colorado 80303-3328

May 1992

U.S. DEPARTMENT OF COMMERCE, Barbara Hackman Franklin, Secretary

TECHNOLOGY ADMINISTRATION, Robert M. White, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, John W. Lyons, Director
t
CONTENTS

1. Introduction 2

2. Important EMC Standards and Regulations 3

2.1 Department of Defense Standards 4

2.2 Civilian Government Agencies 11

2.3 Voluntary Organizations 14

3. General Discussions of Existing Standards 19

3.1 Setting a Realistic Standard Limit 19

3.2 Estimating Measurement Uncertainties 21

3.3 Determining Specifications Based on Technical Justifications . . 21

4. Conclusions and Suggestions 27

5. References 28

iii

EMC Standards and Regulations: A Brief Review

M. T. Ma

Electromagnetic Fields Division

National Institute of Standards and Technology

Boulder, CO 80303

Important current regulations and standards regarding

electromagnetic compatibility (EMC) measurements are reviewed.

These regulations and standards have been either enforced by U, S.

government agencies such as the Federal Communications Commission

and Department of Defense, or incorporated in voluntary industrial

practice. The specific methods and configurations of measurement

required in some of these standards are assessed from a technical

basis to see whether or not they are adequate and appropriate.

Technical deficiencies and potential problems, if any, are pointed

out together with recommendations of alternative and better methods

of measurements. Concurrently, the EMC measurement capability at

the National Institute of Standards and Technology is evaluated and

appraised for the purpose of planning new metrology activities or

programs responsive to the needs of U. S. industry.

Key words: Electric field, electromagnetics, EMC, EMI, emission,

magnetic field, measurement methods, requirement, regulation,

review, standards, susceptibility.
1. Introduction

Increased electromagnetic (EM) pollution in the environment has caused

tremendous concern in the electronics industry and among users. Designers

of components and systems want to be sure that their products do not emit

excessive, unintentional radiation to interfere with the operation of other

systems, nor should these products be susceptible to electromagnetic

interference (EMI), which may degrade their performance. Users of

electronic products also wish to enjoy intra- and inter- system

electromagnetic compatibility (EMC) . To realize this ultimate goal of

achieving total EMC, recommendations, rules, and requirements (under the

general term standards) , are issued by regulatory or private organizations

as mandatory or voluntary guidelines to the system and component designer.

When recommending standards, the proposers have to consider carefully

two important factors, based on sound technical justifications: (1) setting

realistic limits on emission and susceptibility, and (2) offering a clear

set of measurement procedures with appropriate experimental configurations.

Ideally, the emission and susceptibility limits for a piece of

equipment should be specified to represent as closely as possible the EM

environment in an anticipated operational condition for that equipment. If

a susceptibility limit is over-specified, it will cost the industry and

users unnecessarily. For example, if a susceptibility limit to a radiated

electric field for one system component is set at 200 V/m while the actual

worst case under the operational condition is only 100 V/m, a much better

shield would have to be provided to protect this system component for an

electric field at 200 V/m even though a less expensive shield may be

adequate for protecting the system component against the actual electric

field of 100 V/m. On the other hand, a more lenient specification on the

susceptibility limit will not achieve the desired total EMC.

To determine the actual emission or susceptibility value for a piece of

equipment, measurement procedures and equipment configurations must also be

clearly specified within the standard. If they involve any technical

deficiency, the measured results may vary substantially or have no physical

meaning, depending on the actual condition and environment in which the

measurements are performed. When this happens, the EMC objectives will not

be fulfilled; the equipment may not function properly in the operational

condition. Thus, achieving repeatability of the same essential measurement

result, regardless of who is making the measurement, as long as it is done

in the same environment and condition, should be the final objective of

setting any successful standard. In addition, physical interpretations of

the measured results are also important. Do the measured results accurately

represent the fact? Are these results accurate only under the assumptions

made in the standard? What is the expected accuracy? If one or more

assumed conditions are not met, what are then the meanings of the measured

data? What changes are expected in the measured result if one parameter in

the measurement is changed? These questions can only be answered with

adequate understanding of the complicated EM principle.

Unfortunately, users' experience with existing EMC standards indicates

that this is not the case. In particular, the results of the standardized

tests have been inconsistent, and the measurement data obtained in the

laboratory do not correlate well with data obtained under the operational

2
condition. Even the original issuers of some of the standards admit that

key topics, including technical deficiencies, should be addressed when

revising the standards. It is not hard to imagine how costly a questionable

standard can be. Suppose a system designer comes up with a new product,

performs faithfully a successful compliance test in accordance with this

existing questionable standard, and then discovers that the system is still

not electromagnetically compatible in the actual operating environment,

resulting in performance degradation, product damage, or even personnel

injury. This designer will have to find out where the incompatibility is,

modify the design, and then perform the same type of tests without assurance

that the newly modified system will function properly with full EMC. The

procurer of the system ends up paying additional development cost and

suffering a long delay in using the final product.

In supporting the electronics industry to fully comply with the EMC

standards and to minimize test costs by reducing the measurement

uncertainty, the National Institute of Standards and Technology (NIST) is

reviewing the existing EMC-related standards and recommendations. We hope

to identify the problems and deficiencies associated with some of the

current measurement practices, and offer improved alternatives to users,

designers, and regulatory or standard- setting agencies. At the same time,

we are assessing our own EMC metrology capabilities. If there are

inadequacies, we will initiate new metrology programs to provide necessary

assistance to the entire EMC community.

In this study, we restrict ourselves to the review of a few important

U . S . standards being enforced by the regulatory agencies or incorporated in

voluntary industrial practices. The essential points in each standard under

review are summarized and described in section 2 with comments. We then

discuss them in section 3, based on a set of general technical factors and

reasons. Suggestions of whether some of the measurement methods developed

at NIST can be used as alternatives in order to obtain more accurate results

are also presented in section 3. At the same time, our existing measurement

capability and shortcomings are pointed out. Concluding remarks together

with possible future EMC metrology programs to be developed by NIST for

benefiting the electronic industry are given in section 4. In this review

exercise, we concentrate only on radiated emission and susceptibility in

view of our own expertise in these areas, even though conducted emission and

susceptibility are equally important to some applications.

2. Important EMC Standards and Regulations

Without doubt the U. S. Government has been the largest procurer and

user of electronic products and systems. On the military side, the

Department of Defense (DoD) has recognized the importance of EMI control and

issued many specifications and standards [1]. On the civilian side, the

Federal Communications Commission (FCC) , under authority of the

Communications Act of 1934 and its amendment of 1982, is charged with

regulation of the manufacture, import, sale, shipment, and use of electronic

devices and products which may either emit to cause interference to radio

reception or be affected by the EM environment so that their designed

performances are degraded. After conducting many hearings to receive

comments from the industry and general public, the FCC frequently issues

rules and regulations to enforce EMC [2]

3
Other U. S. governmental agencies such as the Food and Drug

Administration (FDA) , Environmental Protection Agency (EPA) , and

Occupational Safety and Health Administration (OSHA) also impose regulations

and standards to implement their own programs. Although these standards are

primarily intended for protecting public health and safety, some of them

cover EMC-related issues [2]

.

To comply with the mandatory standards issued by government agencies,

U. S. industry and some private organizations frequently publish voluntary

EMC recommendations [2] to provide self guidance and promote mutual

understanding

.

Some of the important standards and recommendations from these

governmental and industrial organizations are selected for descriptions and

comments as follows.

2.1 Department of Defense Standards

After experiencing many EMI problems over the years, the DoD has

published, from time to time, a variety of requirements and standards.

Basically, there are three types of documents: (a) principal military EMC

standards, (b) supporting military standards, and (c) military handbooks

(not compliance documents). For this report, we limit ourselves to reviews

of the principal standards [type (a)].

a. MIL-E-6051

This is one of the earliest standards issued by DoD, entitled

"Electromagnetic Compatibility Requirements, Systems," whose latest version

was dated September 7, 1967. This document is intended primarily for

applications to the development of major weapon systems. It emphasizes the

overall requirements for EMC at the system (both airborne and ground) level.

It specifies control of the EM environment, lightning protection, static

electricity, bonding and grounding, degradation criteria and safety margins,

and wiring and cabling. In general, anticipated EMC problems are classified

into three categories, depending on how serious they are:

Category I -- EMC problems that could result in loss of lives, loss of

vehicle, mission aborting, costly delays in launches, or unacceptable

reduction in system effectiveness;

Category II -- EMC problems that could result in injury, damage to

vehicle, or reduction in system effectiveness;

Category III -- EMC problems that result only in annoyance, minor

discomfort, or loss of performance, but not reduction in desired system

effectiveness

.

This standard also addresses EM hazards to personnel and ordnance. It

requires that a system EMC program be established by a contractor with an

EMC board to supervise the program, to set degradation criteria and safety

margins for each subsystem and equipment after consultation with the

procuring authority, to perform the actual EMC tests, and to provide means

of expediting solutions of problems. The document does not discuss EM

coupling mechanisms through which EMI problems may occur. Test methods are

not precisely specified. Expected accuracies in the measurements are not

4
mentioned. In general, the document is vague and incomplete. It is not

easy for users to comply. Success of the standard compliance depends

heavily on the EMC program manager's judgement of each contractor.

b. MIL-STD-461

To extend the application of MIL-E-6051 to a single equipment, the MILSTD-460 series of documents was issued subsequently. The first version,

MIL-STD-461, entitled "Electromagnetic Interference Characteristics,

Requirements for Equipments," was produced and formally published in 1967 as

a result of many committee meetings in DoD. The intent was to improve

coordination among the different services and promote unified procurement

[1]. Its technical objectives are to ensure that interference control is

considered and incorporated into the design of equipment and subsystems, and

to provide a basis for evaluating EMC and effectiveness of systems operated

in a complex EM environment.

This document was revised on August 1, 1968 to become MIL-STD-461A with

the same title. It was then completely reorganized on April 1, 1980, as

MIL-STD-461B with a new title, "Electromagnetic Emission and Susceptibility

Requirements for the Control of Electromagnetic Interference . " This newer

version consists of 10 parts, addressing general and specific requirements.

The latest edition, MIL- STD-461C , with the same title as 461B, was issued on

August 4, 1986 [1]. It has the same basic structure of 10 parts. The major

change was the inclusion of a few new test requirements for considering the

effects due to EM pulses. As a whole, this document spells out everything

in detail. It specifies the emission and susceptibility limits for

different classes of equipment, depending on the type (critical, noncritical; dc, ac, or pulse; narrow band or broadband; etc.) and on where

they are installed (such as aboard aircraft, launch vehicles, surface ships,

submarines , or on ground)

Specific requirements are divided into four categories: conducted

emission, conducted susceptibility, radiated emission, and radiated

susceptibility. In each category, further divisions are made in accordance

with the frequency range or the method involved in the measurement. Details

on the allowed emission and susceptibility limits, frequency ranges, and

measurement procedures are presented in the next section.

c. MIL-STD-462

This standard, entitled "Electromagnetic Interference Characteristics,

Measurement of," issued on July 31, 1967, is considered a companion document

of MIL-STD-461. It establishes techniques to be used for the measurement

and determination of EMI characteristics (both emission and susceptibility)

of electrical, electronic, and electro-mechanical equipment as required in

MIL-STD-461C . Test conditions, preparation of test samples, use of

measurement apparatus , placement and selection of measuring sensors

frequencies, test setup and configurations, and measurement procedures are

all specified. It covers six conducted emission, eight conducted

susceptibility, six radiated emission, and four radiated susceptibility

measurements [1]

For this report, only those parts of these measurements (radiated

emission and susceptibility) which are considered relatively important are

described and commented. Specific features and frequency ranges for each

5
measurement are included. Three of the six radiated emission tests are

concerned with unintentional radiations from the major parts of a system

under consideration. They are summarized as follows.

(1) Method REOl is the one recommended for measuring magnetic fields in the

frequency range of 30 Hz to 30 kHz radiated from each unit in a given

equipment including antenna transmission lines, power cables, and

interconnecting wires. The measurement also applies to radiation due to the

transmitter fundamental and spurious frequencies, and the oscillator. It

specifies a loop antenna (sensor) and an EMI meter as the measuring

apparatus . The sensor is to be placed 7 cm from one face of the equipment

under test (EUT) . The maximum radiated magnetic field for each tuned

frequency in the intended range is detected and recorded by varying the

sensor's orientation with respect to the EUT and scanning the EMI meter.

The measured magnetic field in amperes per meter is then multiplied by the

free -space permeability of 47t x 10 ^ H/m to express it in terms of the

magnetic flux density in teslas. This value is then compared with the limit

specified in MIL- STD-461. The emission limit has been set from 140 dB above

1 pT at 30 Hz to 56 dB above 1 pT for 30 kHz [1]. Whether the measurement

takes place inside an enclosure, in a laboratory environment, or in an open

site is not mentioned. The required measurement accuracy is not specified.

Although magnetic field is the only desired parameter, other important

parameters in this measurement, which will affect the measured results, are

the size (diameter) of the loop antenna, its orientation with respect to the

EUT, its calibration factor, the loop-to-EUT distance, and the environment

in which the measurement is made. While the loop-to-EUT distance of 7 cm

was recommended from a practical consideration, it certainly has no

technical basis. With respect to the intended frequency range, the sensor

is placed within the near range of the emitting EUT. Interaction between

the emitter and sensor is known to be strong under this condition. A minor

change in the distance and orientation of the loop can cause a major

deviation in the measured result. Thus, the physical meaning and accuracy

of the measured data obtained by a user are doubtful.

(2) Method RE02 is designed for measuring the electric field, in the

frequency range of 14 kHz to 10 GHz , radiated from the EUT including cables

and interconnecting wiring. Narrowband emissions are measured from 14 kHz

to 10 times the highest intentionally generated frequency or 1 GHz,

whichever is greater, provided that it does not exceed 10 GHz. For

broadband emissions, the measurements are to be made from 14 kHz to 1 GHz.

The method recommends that a linear dipole be used as the sensing antenna,

for both horizontal and vertical polarizations, together with an EMI meter

to record the maximum reading of the radiated electric field. The linear

dipole is placed at 1 m from the EUT. The measured maximum electric field

is to be compared with the limits specified in MIL- STD-461. For narrowband

emissions, these limits vary from 35 dB/xV/m (decibels above 1 /iV/m) at 14

kHz, decreasing first to 20 dB/iV/m at 28 MHz, and then increasing to 60

dB/iV/m at 10 GHz. For broadband emissions, the allowable limits vary from

100 dB/iV/m/MHz at 14 kHz, decreasing first to 55 dB/iV/m/MHz at 200 MHz, and

then increasing to 70 dB/xV/m/MHz at 1 GHz [1]

.

For testing nonportable EUTs

which are permanently connected either physically or electrically to a

vehicle, it also recommends that the EUT be placed on a ground plane.

Portable EUTs are to be tested inside a shielded enclosure. Again, the

required accuracy is not specified. The parameter to be measured in this

method is thus the radiated electric field from an unknown EUT. The other

6
important parameters, which will change the measurement results, are the

dipole length, its polarization, the calibration factor, the dipole- to- EUT

distance, the size of the ground plane, and whether or not the measurement

is made inside a shielded enclosure. The combined effect of these

parameters on the accuracy of the measurement is very difficult to estimate.

(3) Method RE03 is recommended for the measurement of transmitter spurious

and harmonic emissions in the radiated field, from 10 kHz to 40 GHz.

Specific test frequency ranges are as follows:

EUT Operating Frequency

10 to 30 kHz

30 to 300 kHz

0.3 to 3 MHz

3 to 30 MHz

30 to 300 MHz

300 MHz to 1.24 GHz

Test Frequency Range

10 kHz to 10 MHz

10 kHz to 100 MHz

10 kHz to 600 MHz

10 kHz to 1 GHz

1 MHz to 3 GHz

10 MHz to 12.4 GHz

1.24 GHz and above

1.24 to 5 GHz

above 5 GHz

Lowest frequency is 200 MHz for

coaxial transmission lines, or

0.8 of cutoff frequency for

waveguide transmission lines

Upper frequency is 10 GHz

(required) or 40 GHz (optional)

20 GHz (required) or 40 GHz

(optional)

This method may be used together with Method CE06 (conducted emissions from

antenna terminals, 10 kHz to 26 GHz). However, the method will apply when

the average transmitter output power is greater than 5 kW, the fundamental

transmitter frequency is above 1.24 GHz, and the antenna associated with the

EUT is an integral part of the transmitter (which cannot be replaced by a

dummy load). In addition to an EMI meter, attenuators or amplifiers may be

needed for the measurement, and specific antennas (such as rod antennas,

biconical antennas, or cavity-backed spirals) depending on the frequency

band under 1 GHz are to be used. For frequencies above 1 GHz, it specifies

a spectrum analyzer, traveling -wave tube amplifiers, preselector filters,

frequency counters, and other various cavity-backed spiral antennas. The

measurement is to be performed above a ground plane. It also notes that it

may be necessary to make the measurement in a shielded enclosure , because

the spectrum analyzer may be susceptible to radiated fields . Furthermore

once the radiated fields at a distance from the transmitter being tested are

measured and recorded, the corresponding transmitted power density at the

observation point is computed according to the far- field condition. The

allowable emission limits on electric field set for this case are 10 V/m for

the frequency range from 10 kHz to 30 MHz, 5 V/m from 30 MHz to 10 GHz, and

20 V/m for frequencies above 10 GHz. The required measurement accuracy is

not specified. The important parameters in this measurement, which will

7
affect the measured electric field, are the type and size of the sensing

antenna, its polarization, the calibration of antenna or spectrum analyzer,

the antenna- to- EUT distance, the environment in which the measurement is

made, and the conversion of measured electric fields to power densities

based on the far-field condition. Naturally, the measured results depend

heavily on one or more of the above parameters. Just the environment factor

alone (whether the measurement is performed in a shielded room) could render

the measured results meaningless.

The remaining three radiated emission test methods involve

unintentional emissions (electric or magnetic field) from vehicles, enginedriven equipment, and overhead power lines in the surrounding area of a test

site. No specification on measurement accuracy is given. In all cases, the

sensing antennas are recommended to be placed only at a short distance away

from the emission source, regardless of the frequency involved. The

comments regarding measurement accuracy and physical meaning made for the

above three measurement methods also apply here.

The four radiated susceptibility measurements are described as follows.

(4) Method RSOl is recommended for determining whether class I equipment

(those which must operate compatibly when installed in critical areas) is

susceptible to radiated magnetic fields from 30 Hz to 30 kHz. Cables and

connectors attached to the EUT are included. The method requires a loop as

the simulated radiating antenna and a signal source capable of producing an

approximate magnetic flux density of 50 /iT, at a test point 5 cm from the

loop face. The plane of the loop is parallel to the plane of the test

sample surface. An EMI meter or a narrow-band voltmeter is to be used to

verify the anticipated magnetic flux. The susceptibility limits in terms of

the magnetic flux density are from 160 dB above 1 pT at 30 Hz decreasing to

78 dB above 1 pT at 30 kHz. The frequencies and the minimum field which

causes noticeable susceptibility problems (permanent malfunction or

degradation of performance beyond the specified equipment tolerance) in the

EUT are recorded. No measurement accuracy is specified. Hence, the

measurement parameter is the magnetic field at a distance of 5 cm from the

radiating loop, which may cause EMI problem to an EUT. The other important

parameters , which will influence the measured results , in this measurement

are the loop antenna size, its orientation and calibration, and the distance

at which a prespecified magnetic field is produced. Because of large

variations in the magnetic field produced by a radiating loop in the nearfield environment, a successful test of passing the susceptibility criterion

of a given EUT at the distance of 5 cm from the source does not necessarily

imply that another test of the same EUT at a greater distance from the same

source will again be successful.

(5) Method RS02 is recommended for determining the susceptibility of class I

equipment to magnetic induction fields produced by current-carrying wires.

The method is intended mainly for testing cables and cases in which an EUT

is placed. Two tests, power frequency test and spike test, are required for

evaluating both cable and case susceptibility. Specific waveforms and pulse

widths are recommended for the tests [1]. No measurement accuracy is

required. Besides the measurement parameter of magnetic induction, the

other important influencing parameters in this measurement are the cable

length, its shielding material, the case dimensions, and the test waveform

and pulse width. Combined effect of these parameters could make the

measured results unpredictable. Passing of susceptibility test for a cable

8
of a given length does not warrant passing for another cable of a different

length

(6) Method RS03 is to be used for determining whether or not an EUT exhibits

any degradation of performance, malfunctioning, or other undesirable effects

when it is immersed in an electric field in the frequency range of 14 kHz to

10 GHz. The recommended susceptibility limits for all surface ships under

the U. S. Navy are 10 V/m below decks with metallic hulls, 50 V/m below

decks with nonmetallic hulls, and 200 V/m above decks (areas exposed to

weather) [1]

This method applies only to class I equipment. It recommends

that a signal source, an EMI meter, antennas depending on frequency bands,

and an output monitor be used in the measurement. The results consist of

recording frequencies at which the EUT is susceptible and the threshold

susceptibility level at each frequency. A specific measurement accuracy is

not required.

When a large EUT is involved in a testing field, the transmitting

antenna is recommended to be placed at a distance sufficiently large from

the EUT to allow it to fall within the half -power beamwidth of the antenna.

If a very high electric field is to be generated for the lower frequency

end, from 14 kHz to 30 MHz, a long-wire antenna installed inside a shielding

enclosure is specified. Alternatively, a parallel stripline may be used to

generate high, broadband, electric fields. The desired measurement

parameter is generation of electric field. The other influencing parameters

in this measurement are type and size of the radiating antenna, its

orientation, the calibration factor, the size of the intended EUT, the

antenna- to -EUT distance, and the susceptibility limit at a specific

location. The long- wire antenna is known to be broadband (advantage) but

with high radiations from the sidelobe directions (disadvantage) . Placing

this antenna in a shielded enclosure can produce large variations in

electric field produced at a given distance. Passing a susceptibility test

of an EUT under this unpredictable field environment is meaningless.

Therefore, the recommended measurement practice for low frequencies is not

based on a sound technical foundation.

(7) Method RS04 should be employed to determine equipment susceptibility to

radiated fields of specified spectral content and intensity in the frequency

range of 14 kHz to 30 MHz. A unique feature is the use of a parallel-plate

transmission line to produce necessary electric and magnetic fields. It

recommends that the EUT be tested with only two orientations when it is

placed inside the line. No particular susceptibility limits nor measurement

accuracy are specified. Test results include the frequency and the minimum

fields to which the EUT is susceptible. The important parameters in this

measurement are the method used to produce specified radiated fields, the

geometry of the parallel-plate line, and the EUT orientation with respect to

the testing fields. While this method is technically more justifiable than

the other methods presented so far, the requirement of only two EUT

orientations may not be sufficient to determine the overall susceptibility

of the EUT, depending on the actual situation involved. Also, the

electromagnetic field produced inside an empty parallel -plate line without

EUT can be substantially different from that with EUT. It depends on the

EUT size relative to the space between the plates. Thus, the susceptibility

limit established for a given EUT inside the parallel-plate line can be

different from that when it is placed in the actual operational environment.

This kind of perturbation effect should be kept in the users' mind when a

high degree of accuracy is desired.

9
This summary covers some of the methods recommended in MIL-STD-462.

Five more "Notices" that represent minor additions and modifications, issued

at later dates, are also attached to MIL-STD-462 as a package. Another

companion standard is MIL-STD-463, entitled "Definitions and Systems of

Units, Electromagnetic Interference and Electromagnetic Compatibility

Technology," dated June 1, 1977 [1]. This document merely clarifies some

commonly used EMI/EMC terminology and emphasizes the use of SI units based

on NBS (now NIST) recommendations, even though English units were actually

used many times in the standard.

d. MIL-STD-285

This standard, "Attenuation Measurements for Enclosures,

Electromagnetic Shielding, for Electronic Test Purposes, Method of," was

issued on June 25, 1956 [1]. The document describes a method for measuring

the attenuation characteristics of shielding enclosures of different sizes

over the frequency range of 100 kHz to 10 GHz. The parameter of interest in

this method is, thus, the electric- field or magnetic- field attenuation

characteristics or the shielding effectiveness of the enclosure under test.

For the sub-band of 150 kHz to 200 kHz, it recommends that a specific signal

source, low- impedance vertical loop antennas of 0.3 m in diameter for both

transmitting and receiving, and a detector be used to determine the

magnetic -field attenuation of the enclosure. The loops are placed 0.3 m

away from the enclosure wall.

For the frequency range of 200 kHz to 18 MHz, it recommends that highimpedance rod antennas (also vertical) of 1.04 m in length together with the

signal source and detector be used to measure the electric-field attenuation

of the enclosure. The rod antennas are placed at a distance of 0.3 m from

the enclosure wall.

For the frequency of 400 MHz, it recommends that tuned vertical dipoles

be used as the transmitting and receiving antennas with the same set of

other apparatus. The transmitting dipole is to be placed at least 1.83 m

and the receiving dipole at least 0.05 m away from the enclosure wall.

In all of these three cases, the transmitting antenna is to be placed

outside the enclosure with the receiving antenna inside the enclosure during

the measurement.

The important influencing parameters in this standard are the size and

orientation of the transmitting and receiving antennas, their calibration

factors, their respective locations relative to the enclosure wall,

frequency, and the wall material. The measurement of attenuation

characteristics of an enclosure or of a material is known to depend not only

on the enclosure or material itself, but also on the wave type generated by

a transmitting antenna (plane wave vs. near-field wave, high- impedance wave

vs. low- impedance wave, wave polarization and propagation direction, the

environment in which the antenna is placed, etc.), the location and

orientation of the receiving antenna and the environment in which it

operates, and the calibration factors of both antennas. The response of a

receiving antenna placed inside an enclosure represents the vector sum of

the direct wave passing through the enclosure and the wave components

reflected from the other enclosure walls. As a result, the measurement

accuracy of this standard is very questionable. It has been recognized in

10
the EMC community that users can produce any attenuation results as they

please

e. MIL-STD-1344A, Method 3008

This standard, "Shielding Effectiveness of Multicontact Connectors,"

issued on August 14, 1981, was prepared for measuring the leakage from the

connector-pair interface of a multicontact connector inside a mode -stirred

chamber and determining its shielding effectiveness in the frequency range

of 1 to 10 GHz. It recommends that a signal source capable of producing an

output power of minimum 1 W, an isolator, a frequency counter, a prepared

shielded cable, directional couplers, power meters, 50-fi loads, and

attenuators be used as the test apparatus. Long wires are to be used as the

input and reference antennas

Two measurements are made at each frequency to obtain the average power

received by the reference antenna and the average power received by the

connector, both over one complete revolution of mode -stirrer rotation. The

ratio of these two measured results defines the shielding effectiveness of

the connector. Measurement accuracy is not specified. The important

factors to be considered in this measurement are the selection of sample

multicontact connectors, identification of a coupling mechanism with which

the field penetrates into the connector, understanding of the field

generated inside a mode -stirred chamber, the location of the test sample

placed inside the chamber, and interpretation of the measurement results.

The relative uniformity of electric fields generated inside a modestirred chamber depends on frequency, the number of modes existing in a

given chamber, mode density, chamber dimensions, and the quality factor (Q)

as a function of chamber material. While the field uniformity is in general

much better than that generated inside a shield enclosure, it still can have

a variation as large as 5 to 8 dB, depending on how the chamber is designed.

2.2 Civilian Government Agencies

a. Federal Communications Commission

The major parts of the FCC rules and regulations, as related to EMC,

are contained in Title 47, Parts 15, 18, and 68 of the U. S. Code of Federal

Regulations, of which Parts 15 and 18 are the relatively important ones [2].

Part 15, "Radio Frequency Devices" (53 pages), defines and sets EMI

standards for unlicensed incidental and restricted radiation devices.

Operation of any such device without meeting Part 15 provisions is

prohibited. Of particular interest is Subpart J, "Computing Devices," which

covers EMI limits for class A (commercial, industrial, and business) and

class B (consumer) computing devices. Frequency ranges considered for class

A are three specific bands: 30 to 88 MHz, 88 to 216 MHz, and 216 to 1000

MHz. The maximum allowable emanations (in terms of electric fields) which

may be leaked from these devices at a distance of 30 m are respectively 30,

50, and 70 /iV/m. A shorter distance may be used for the measurement if the

test results are correlatable with that at 30 m according to the inverse

distance relationship. For class B computing devices the respective maximum

allowable radiated electric fields in the same three frequency bands but at

a distance of 3m are 100, 150, and 200 /iV/m. If, however, this required

distance of 3 m is impractical because of the EUT size and location.

11
measurements may be made at a further distance up to 30 m and the measured

results correlatable with those at 3 m according to the inverse -distance

relationship

.

The method and procedures for measuring the unintentional emissions

from these computing devices are described in FCC/OET (Office of Engineering

and Technology) MP-4, "FCC Procedures for Measuring RF Emissions from

Computing Devices" (24 pages). It requires that measurements of radiated

emission be made in an open flat area. A ground screen is highly

recommended, but not mandatory. If a radiating device or equipment cannot

be set up on an open-field test site, testing is permitted at the user's

premises. In this case, both the equipment and its location are considered

the EUT. The measured emissions are then unique to that particular

installation.

This standard also recommends that a tuned half-wave dipole antenna be

used for measuring the radiated electric field over the entire frequency

range of 30 to 1000 MHz. Measurement accuracy is not specified. At the

lower frequency end such as 30 MHz, the dipole length will be 5 m, which is

too long to be practical. In this or other cases, a different linearly

polarized antenna may be used, provided that the result obtained with such

an antenna is correlatable with that obtained with a tuned half-wave dipole.

The antenna must be capable of measuring both horizontal and vertical

polarizations. The antenna height (measured from the feed point) above

ground is to be varied, dependent on the horizontal antenna- to -EUT distance,

in order to measure the maximum radiated strength. For measurement

distances up to and including 10 m, the antenna height is varied from 1 to 4

m. At a distance of 30 m, the antenna height is varied from 2 to 6 m. At

intermediate distances from 10 m to 30 m, it may be necessary to adjust the

minimum antenna height down to 1 m, except that, for vertical polarization,

the minimum antenna height has to be increased so that the bottom half of

the dipole clears the site ground surface by at least 25 cm.

Radiated measurements made inside a shielded enclosure are suitable

only for determining the frequency of each emission from an EUT. Measured

results of electric field in the enclosure environment vary substantially

because of multiple reflections of the emission from enclosure walls, and,

therefore, are not reliable.

The important parameters relevant to this standard include the size of

ground screen if needed, the antenna calibration factor, antenna locations

relative to the EUT, EUT configurations, and test environment. Response at

the receiving dipole is a vector sum of the emission radiated directly from

an EUT placed in the open ground and the emission from the EUT's ground

image. Consequently, the final result depends on earth constants (mostly

conductivity and permittivity) and the size and design of the ground screen.

Furthermore, how the receiving dipole is calibrated is also important in

determining the measurement accuracy. In general, a commercially available

dipole is almost exclusively calibrated in the far field. The effect on

measurement accuracy when the dipole is placed within the near -field range

of the EUT is usually not estimated. The environment in the surrounding

area of an open site, such as scattering objects, obstacles, vegetation and

others is another important factor to be considered in this method of

measurement

.

12
Recently, FCC proposed adopting ANSI C63.4 (see section 2.3) as its

official measurement standard for digital devices to replace its own MP-4

[3-4].

Part 18, "Industrial, Scientific and Medical Equipment" (7 pages), sets

the EMI emission limits for the industrial, scientific, and medical (ISM)

equipment, which may be operated on any frequency above 9 kHz except a few

prohibited bands, which are reserved for safety, search, and rescue

purposes: 490 to 510 kHz, 2.17 to 2.194 MHz, 8.354 to 8.374 MHz, 121.4 to

121.6 MHz, 156.7 to 156.9 MHz, and 242.8 to 243.2 MHz. The ISM equipment

operating on a set of specific frequencies (6.78, 13.56, 27.12, 40.68, 915

MHz; 2.45, 5.8, 24.125, 61.25, 122.5, and 245 GHz with certain small

tolerances) is allowed unlimited radiation. This could cause EMI problems

to other co- located equipment. The average annual number of verified

complaints on interference from ISM equipment during the past few years is a

little over 100. It represents only about 0.14% of the total annual number

of verified complaints from all man-made sources of interference. For other

frequencies, there are some limits. But the maximum allowable radiated

electric-field limits are, in general, less restrictive than those in Part

15. Technical standards on frequency tolerance and field limits are

detailed in Subpart C. The measurement techniques to be used to determine

compliance with the requirement are described in MP-5, "Methods of

Measurements of Radio Noise Emissions from ISM Equipment."

Part 68, "Connection of Terminal Equipment to the Telephone Network"

(146 pages)

provides uniform standards for protection of telephone network

from terminal equipment and the associated wiring. It also discusses the

problem of compatibility of hearing aids with the telephone system.

Basically, the problems addressed in Part 68 are conducted (rather than

radiated) EMC in nature.

b. Food and Drug Administration

This agency, under the Center for Devices and Radiological Health

(CDRH) of the U. S. Department of Health and Human Services, develops and

implements national programs for protecting public health concerning medical

devices and radiological technology. Most of their standards are related to

health issues. There are, however, a few EMC -related topics such as the

performance standards for electronic, ionizing radiation, and microwave/rf

emitting products, which are included in Title 21, "Food and Drugs" (9

volumes). Subchapter J. Another document of EMC interest is MDS-201-0004

"Electromagnetic Compatibility Standards for Medical Devices" (62 pages)

which covers emission and susceptibility requirements and test methods for

medical devices [2]. Some restrictions on emissions from medical devices

should, perhaps, be imposed in view of the fact that FCC allows unlimited

radiations for certain frequency bands from the ISM equipment. One more

publication, FDA 87-4219, "Medical Devices Standards Activities Report,"

provides a comprehensive listing of national and international, voluntary,

and regulatory standards activities for medical devices.

13
c. Environmental Protection Agency and Others

The EPA exercises statutory authority in providing public safety in the

areas of toxic substances, clean water, energy, and clean air. The three

documents issued by EPA [2],

SAR No. 1161, "Guidance for Occupational Radiation Exposure,"

SAR No. 1525, "Radiofrequency Radiation Guidance," and

EPA 2663, "Biological Effects of Radiofrequency Radiation,"

address the health-related issues which also have EMC impacts. Specifically,

the effects of radiated fields on human health are of their concern. While

experimental studies in this area under the support of EPA have been

performed for many years, no reports concerning solid evidences of long-term

low-level exposure of radiated fields on human health have been issued.

Other government agencies such as the National Institute for

Occupational Safety and Health in the U. S. Department of Labor also, from

time to time, issue regulations regarding safety. These regulations may

also have EMC consequences, but are not considered as important as those by

FCC.

2 . 3 Voluntary Organizations

Because the standards suggested by the organizations to be described in

this section are voluntary, the working committees under these organizations

wisely concentrated on recommendations of measurement methods, experimental

setups, designs and arrangement of components to reduce rf emissions or to

increase immunity, and performance requirements of instruments, rather than

recommendations of specific emission and immunity limits as in MIL-STD-461.

Setting emission limits may be useful in practice, because the ultimate goal

is to encourage reducing unnecessary leakage which can cause interference

problems to others. It is much more difficult to specify realistic immunity

limits because of the dependence of actual environment under which a device

or system is to be operated. A more practical approach is to determine the

susceptibility (or immunity) of an electronic product based on a good

measurement method and then to determine whether this product can function

normally in a given EM environment.

a. American National Standards Institute

Founded in 1918, ANSI is an association of industrial concerns, trade

organizations, technical societies, labor and consumer organizations, and

government agencies. It recommends national voluntary standards in safety,

engineering, and technical fields. It also offers information on foreign

standards and represents the United States in international standardization

coordinations. The standards issued by ANSI are usually the products of

many working committees. Of particular interest to EMC community is

Committee C63 (Radio-Electrical Coordination)

.

The standard C63.2-1987, "Electromagnetic Noise and Field Strength, 10

kHz to 40 GHz -- Specifications," describes the requirements for

instrumentation used to measure peak, quasi-peak, rms , or average values of

14
EM noise and fields in the indicated frequency range. The basic apparatus

is a frequency- selective voltmeter. With appropriate coupling devices such

as antennas and current probes, the instrument also measures other physical

quantities such as the current and voltage. The required measurement

accuracies are ±2 dB in voltmeter, ±3 dB in field strength, and ±2% in

frequency. It recommends that different antennas be used as radiated field

sensors in different frequency bands. They are rod or loop antenna (0.01 to

30 MHz) , tuned dipole antenna (30 to 1000 MHz) , biconical antenna (30 to 220

MHz) , log-periodic and conical log-spiral (220 to 1000 MHz) , conical logspiral (1 to 10 GHz) , double -ridged waveguide (1 to 18 GHz) , and matched

waveguide horn (18 to 40 GHz) . While these antennas are adequate to cover

the entire intended frequency range, consistency in calibrating various

antennas in different operating environments is still a problem area.

Ideally, antennas with much broader frequency band of operation to reduce

the required number of sensors are needed.

The standard C63.4-1981, "Radio Noise Emission from Low-Voltage

Electrical and Electronic Equipment in the Range of 10 kHz to 1 GHz," sets

forth uniform methods for measuring radiated and power- line conducted radio

noise emitted from this category of equipment in the indicated frequency

range. The methods apply to the measurement of individual components and

units, subsystems, or systems. It also specifies for the test site

environment an open field with an elliptically shaped ground plane free of

reflecting objects as the condition to ensure valid, repeatable measurement

results. The ambient noise and other undesired signals should be at least 6

dB below the allowable limit of the applicable standard when the EUT is deenergized. By comparison to the FCC standard, this standard is issued after

more careful technical considerations. This standard also specifies an

alternative measurement environment (shielded enclosure) for frequencies

below its lowest resonant frequency. Measurements made inside the enclosure

are permitted at a distance of 1 m between the EUT and sensor. The

measurement data may be extrapolated to other distances only if the

extrapolation can be shown to produce valid results. What constitutes

validity is, however, not clearly shown. In view of the comments made

earlier, it is doubtful that measurement results obtained in a shielded

enclosure can be considered valid. The most recent version of this standard

was dated in 1991. The part concerning the measurement for digital devices

has been adopted by FCC to replace FCC MP-4 [3-4]

The standard C63. 12-1984, "Procedures for Control of System

Electromagnetic Compatibility, Recommended Practice on," discusses the

nature of both man-made and natural environmental rf noise, identifies

several types of devices used for measuring the noise, and suggests limits

for emission and susceptibility subject to various environmental

constraints. To the extent that rf noise varies in time and space, a

statistical means is, perhaps, the best method used to describe it.

Another ANSI Committee C95 on Radiation Hazards dealing exclusively

with health issues no longer exists. Its main function is now carried in

IEEE Standards Coordinating Committee SCC-28 on Non- Ionizing Radiation. One

of the standards published by the old Committee C95 is C95. 1-1982, "Safety

Levels with Respect to Human Exposure to Radio Frequency Electromagnetic

Fields, 300 kHz to 100 GHz." This standard recommends protection guides to

prevent biological injury from exposure to EM radiation in the indicated

frequency range. These recommendations are intended to apply to nonoccupational as well as occupational exposures . In terms of the mean

15
squared electric field (E^), the mean squared magnetic field (H^), and the

equivalent far-field free-space power density (S) , the recommended exposure

limits are as follows:

Frequency Range E2 H2 S

(MHz) (V2/m2) (A2/m2

)

(mW/cm2

)

0.3 - 3 400 000 2.5 100

3 30 4 000 (900/f2) 0.025 (900/f2) 900/f2

30 300 4 000 0.025 1

300 1 500 4 000 (f/300) 0.025 (f/300) f/300

1 500 100 000 20 000 0.125 5

The frequency f in the above table is expressed in megahertz. This

standard, while on a much conservative protection level as compared to other

international standards, can be used to supplement the EPA standard

described above.

In addition, ANSI also publishes standards jointly with the Institute

of Electrical and Electronics Engineers (IEEE). Examples are:

ANSI/IEEE Standard 748-1979, "IEEE Standard for Spectrum Analyzers,"

and

ANSI/IEEE Standard 430-1986, "Measurement of Radio Noise from

Overhead Power Lines and Substations, Standard Procedures for

the . "

b. American Society for Testing and Materials

The ASTM has become one of the largest voluntary standards organization

in the world with more than 32 000 members. It publishes test methods,

specifications, practices, guides, and classifications for materials. The

EMC/EMI aspect of its work is the responsibility of subcommittee D09.12 on

Electrical Tests, under Committee D9 on Electrical and Electronic Insulating

Materials. Its recent standard, D 4935-89, "Standard Test Method for

Measuring the Electromagnetic Shielding Effectiveness of Planar Materials,"

was issued based on the far-field method as recommended by NIST [5-7]

.

This

is a much more meaningful standard than MIL-STD-285. A method for measuring

the same material in a near- field environment and one for measuring

shielding effectiveness of containers and gaskets are still needed.

c. Institute of Electrical and Electronics Engineers

The IEEE standards are normally developed by the technical committees

of its various Societies and the Standards Coordinating Committees. The

EMC -related standards are usually prepared by the committees under its

Society of Electromagnetic Compatibility. Sample rf standards are [2]

IEEE Standard 140-1950, "Minimization of Interference from RF Heating

Equipment, Recommended Practice for,"

IEEE Standard 139-1952, "Field Intensity above 300 MHz for RF

Industrial, Scientific and Medical Instruments, Recommended Practice

for Measurement of," and

16
IEEE Standard 299-1969, "High Performance Shielding Enclosures,

Trial -Use Recommended Practice for Measurement of Shielding

Effectiveness .

The first document reviews the theoretical aspects of the EMI problem

due to rf heating equipment and outlines procedures and required instruments

for measuring emissions in the frequency range from 20 kHz to 200 MHz. Some

remedial means for reducing the emission in order to comply with the FCC

rules are also suggested.

The second document is aimed specifically at ISM equipment. Topics

include measurement methods, antenna design, receivers, other measuring

equipment, and precautions for ensuring measurement accuracy. This standard

is very useful to determine the emission for frequencies above 300 MHz,

especially in view of the fact that Part 18 of the FCC standard allows

unlimited radiation from ISM equipment for some frequency bands in the

frequency range outlined in this standard.

The third standard recommends uniform test procedures and estimation

techniques to determine the effectiveness of room- sized high-performance

shielding enclosures over three frequency bands: from 100 Hz to 20 MHz, from

300 MHz to 1 GHz, and from 1.7 to 12.4 GHz. In the lowest frequency band,

small and large loops are used for measuring the magnetic field near the

enclosure wall. In the middle frequency band, dipole- to -dipole tests for

measuring the electric field are delineated. For the highest frequency

band, power measurements are recommended. Recognizing the dependence of

measured results on frequency and position of the sensor, the committee

preparing this standard emphasizes that the measured result only represents

the shielding effectiveness for that specific test and procedure. Some

tests and procedures even require multiple measurements of a similar

performance feature at different locations or with different polarizations.

For a given procedure, the minimum and average shielding effectiveness will

be reported. Clearly, this standard is more carefully drafted as compared

to MIL- STD- 285. However, this standard is still not general enough for

accurately determining the shielding effectiveness of an enclosure.

d. Society of Automotive Engineers

The SAE, founded in 1905, is a nonprofit organization dedicated to "the

advancement of mobility technology to better serve humanity." It develops

technical information on all forms of self-propelled vehicles and

disseminates such information through meetings and reports. All documents

prepared by SAE are submitted to ANSI for recognition as possible ANSI

standards. Although compliance with SAE standards is voluntary, nearly 200

of them have been adopted by DoD as mandatory. SAE has also been an

important source of aerospace standards through its Aerospace Engine

Division.

The EMC issues are addressed by SAE Committee AE-4, which assists the

technical community with standardization and improved design and test

methodology. It emphasizes the concept of "design before fact." Committee

AE-4 has published various documents applicable to vehicular EMC. Of

particular interest is the SAE Aerospace EMC Handbook, which is a collection

of AIRs (aerospace information reports) and ARPs (aerospace recommended

practices). Some important ones include [2]:

17
SAE AIR 1209, "Construction and Calibration of Parallel Plate

Transmission Line for EMI Susceptibi._ ity Testing,"

SAE AIR 1255, "Spectrum Analyzers for EMI Measurements," and

SAE AIR 1509, "EMC Antennas and Antenna Factors: How to Use Them?"

The other well-known standard, SAE J1113, "Electromagnetic

Susceptibility Procedures for Vehicle Components (except Aircraft)," was

developed by the SAE Subcommittee on EMI Standards and Test Methods. It

discusses the measurement methods and requirements for determining the

susceptibility of vehicle systems to radiated magnetic and electric fields

in different frequency bands. Generally, it includes more technical aspects

than those in FCC regulations. In particular, one section recommends that a

transverse electromagnetic (TEM) cell be used for determining the electricfield susceptibility of equipment for frequencies from 14 kHz to 200 MHz.

Another section covers the requirements for determining susceptibility of

automotive electronic equipment, subsystems, and systems to electrostatic

discharges (ESD) . In this latter aspect, it recommends an ESD test by

direct contact.

e. Radio Technical Commission for Aeronautics

The standards issued by the RTCA are mainly related to aviation, air

traffic control, and communications. Its activity in the EMC area is

focused on rf interference to aeronautical radio systems. It has published

three well -received documents [2]

DO-119, "Interference to Aircraft Electronic Equipment from Devices

Carried Aboard,"

DO-127, "Standard Procedure for the Measurement of the RF Radiation

from Aviation Radio Receivers Operating within 30-890 MHz," and

DO-160C, "Environmental Conditions and Test Procedures for Airborne

Equipment .

The first document listed above recommends that permissible rf

radiation from portable equipment used in flight be limited to avoid

interference with the aircraft operating equipment. The second one

recommends that a far- field method be used for making necessary measurement

in that particular frequency range. Section 20 of the third standard

describes the tests for determining whether equipment will operate within

performance specifications when the equipment and its interconnecting wiring

are exposed to rf modulated power, either by a radiated field or by

injection probe induction onto the power lines and interface circuit wiring.

Whether these test methods will produce equivalent results are not seriously

addressed.

f. Electronic Industries Association

The EIA represents electronics manufacturers in all categories. Its

250 standing committees have produced more than 500 EIA engineering

standards. The EIA Government EMC Committee, G-46, serves as an advocate of

industrial positions regarding government specifications, standards, and

regulations. Its duties include reviewing and coordinating related

18
activities by government, industry, and its members to make sure that EMCoriented regulations and standards are adequate and appropriate. It also

makes proposals and recommendations for actions. Quite often government

agencies also submit proposed regulations for EIA reviews and comments.

One of the EIA standards, EIA-378, "Measurement of Spurious Radiation

from FM and TV Broadcast Receivers in the Frequency Range of 100 to 1000

MHz, Using the EIA-Laurel Broadband Antenna," was issued in response to the

commonly recognized fact that the local oscillators and other components of

superheterodyne receivers in broadcasting stations can be sources of

spurious radiations and cause interference to others. This standard

describes setups and techniques for measuring these radiations

g. Computer and Business Equipment Manufacturers Association

The products made by the member companies represented by the CBEMA

constitute almost 4% of the U. S. gross national product. Although CBEiiA

does not directly publish standards, its members work closely with other

voluntary organizations such as ANSI and IEEE to offer input information,

guidance, and opinion. The subcommittee SC5 on EMI of its Environment and

Safety Committee published a report in 1977, "Limits and Methods of

Measurement of Electromagnetic Emanations from Electronic Data Processing

Equipment" [2]

Although this report is not a standard, it can be used as a

valuable reference or supplementary document when considering FCC Part 15.

h. Others

Another widely recognized organization. Underwriters Laboratories (UL)

lists products and systems made by various industries, that have been

evaluated by them for hazards to life and property. It issues frequently

the basic engineering requirements for the products under various

categories. These requirements are based on sound engineering principles,

research results, tests, and field experience. Its activity in EMC,

however, is limited to simple facilities such as a roof-top ground screen

for calibrating antennas and for measuring emissions from electronic

products

3. General Discussions of Existing Standards

After describing the key existing EMC standards with brief comments, we

now offer in this section detailed technical discussions and analysis that

may help reduce or eliminate some of these EMI problems when taken into

consideration for the revision of the standards. In this exercise, we

suggest some measurement techniques developed at NIST, which may be used as

alternatives to those in the existing standards in order to obtain more

accurate results. At the same time, our EMC metrology and service

capability for supporting the electronic industry is appraised. New

research and measurement programs are also identified to strengthen our

position to provide better services to the EMC community.

3.1 Setting a Realistic Standard Limit

As was emphasized in the introduction of this report, an EM

susceptibility limit should be set to represent the actual EM environment in

which the equipment is to be operated. For a confined location such as on a

military surface ship or inside an aircraft, many intentional sources

19
including various antennas and transmitters are designed and installed for

meeting certain objectives. The EM fields generated by these sources in the

sidelobe regions, together with the fields from unintentional sources, are

time varying in that not all sources may be emitting simultaneously.

Conservatively, a worst case based on the set of available information on

frequency, power, distance, direction, and time of operation may be adopted

as the susceptibility limit. In some cases in an enclosed environment such

as aircraft or helicopters, the effects of resonant frequencies and their

corresponding quality factors (Q) should also be analyzed and taken into

consideration. Furthermore, for special localities such as those areas

surrounding major airports, various radars for different purposes and other

emitting sources are present. A reliable method, based either on a

theoretical model or on actual measurement data, for determining a realistic

field environment is important for the aerospace industry. The results of

fields may be expressed in terms of peak or average values with a prescribed

accuracy limit and degree of confidence. This type of information is to be

used by the aerospace industry to evaluate whether the electronics aboard

the aircraft are compatible with that particular field environment.

Deriving a statistical model for characterizing the field environment near

major airports, based on published knowledge on the topic through literature

survey or by modified methods, deserves to be considered one of our future

research activities.

For other locations not so confined or well defined, it may be hard to

specify a realistic susceptibility limit. When a limit is over-specified,

it will ensure EMC even though it may cost users unnecessarily. On the

other hand, if a limit is under-specified, an EMI problem will result. A

case in this category is evidenced by the recent incident related to the U.

S. Army Apache Helicopter program [8]. This helicopter was primarily

designed as an airborne anti-tank weapon, a $13 billion project. Since

production began in January, 1984, approximately 700 of the projected 807

total production have been delivered to the Army. According to the

specifications contained in MIL-STD-462, equipment and subsystems intended

for use in aircraft purchased by the U. S. Navy and Air Force are expected

to meet the rather strict susceptibility (or immunity) limit of 200 V/m for

electric fields (because of their special, confined operating location where

so many high-power sources are present). However, for the aircraft ordered

by the Army, an immunity limit of 20 V/m may be specified because of their

typical operating environment. This lower immunity limit was actually used

in the Army Apache Helicopter program. As a consequence, a severe EMI

compatibility problem has been discovered. Specifically, EMI causes

uncommanded stabilator movement and other difficulties in the automatic

flight control system, vertical instrumentation display system, ac and dc

power systems, fire detection system, blade de-icer system, and command

instrument system. In fact, the helicopter experiences EMI problems even

when operated in radiated fields from low-level emitters such as commercial

microwave devices, television stations, and airport radars [8].

The modernization effort of military hardware is continuing and is

often achieved by adding transmitters with higher power and better signal

processors with lower power requirements, EMI problems will likely be

experienced more frequently in the future if susceptibility limits are not

realistically established.

20
3.2 Estimating Measurement Uncertainties

The most serious deficiency in existing standards is perhaps a lack of

technical basis for estimating measurement uncertainties. This explains why

so many measurements recommended in the standards fail to yield repeatable

results within the uncertainty. When the actual results of the same

measurement under the same condition vary by a large amount of, say, ±40 dB

such as those experienced with the emission and susceptibility measurements

made inside a shielded enclosure or with the shielding effectiveness

measurement of materials and enclosures, the measurements as specified in

the standard are obviously useless. However, a required uncertainty for

certain measurements cannot be prespecified in general. This is so because

it may never be realizable. The important issue is to be able to estimate

measurement uncertainties for a given measurement method and environment

based on technical reasons or theoretical computations. A comparison of

experimental and computational results is always helpful. Uncertainties due

to equipment imperfection, technical difficulties, or unrealistic

assumptions included in the theoretical models may then be analyzed and

estimated. Changes in the measured data due to changes in one or more

measurement parameters should be predictable. Similarly, estimates of

changes in characteristics of EUTs from a laboratory environment to a field

environment should also be made. These factors should be taken into

consideration when revising the standards in the future.

3.3 Determining Specifications Based on Technical Justifications

A closer examination of the specifications contained in the standards

reveals again that the most serious shortcomings are often due to a lack of

understanding of the EM coupling mechanisms and the antenna characteristics

in different environment (such as far-field or near-field). The

specifications, therefore, do not rest on a sound technical basis. Some

examples are discussed as follows

a. Separation between Antenna and EUT

In many measurement methods suggested in MIL-STD-462, such as Methods

REOl and RSOl for determining the emission and susceptibility of radiated

magnetic fields, only small separations such as 7 cm or 5 cm between the EUT

and a sensor for REOl (or a radiator for RSOl) were specified. While this

specification of separation may be due to practical considerations, these

distances are obviously electrically short for the intended frequency range

of 30 Hz to 30 kHz. When the EUT and a sensor (or a radiator) are within

the near- field region of each other, the field structure at the sensor or

radiator is very complex and sensitive to minor changes in distances or

other parameters. Further, the coupling between the EUT and sensor (or

radiator) is more severe when the separation is so short. This is one of

the reasons why many measurement results do not agree with each other.

Two stable and reliable methods developed at NIST are based on sound

theoretical considerations and involve a TEM cell or three orthogonal loops

to achieve the same purpose. Since both the TEM cell and loop antennas are

good primarily for low frequencies, they are suitable for this application.

For determining the magnetic field radiated from an unknown source, the EUT

under investigation is placed inside a TEM cell and rotated systematically.

Measurements of the difference power outputs from the two ends of the TEM

21
cell will yield a set of equivalent magnetic dipole moments to represent the

EUT, from which the corresponding radiated magnetic field in free space can

then be calculated [9, 10]. This method will eliminate the problem due to a

short separation of 7 cm in Method REOl. In fact, another advantage is that

no sensing antenna is needed in this case. This same method yields

simultaneously the equivalent electric dipole moments and hence the electric

field radiated by the same unknown EUT at low frequencies if the sum power

outputs of the TEM cell are measured. This method also eliminates the

specification of 1 m for the separation as recommended in Method RE02 and

thus can be used to replace the arbitrary requirement of separation distance

in that method and Method RE03 (low-frequency portion). The use of a

shielded enclosure as recommended in Method RE03 and ANSI C63.4 can also be

avoided, thereby eliminating the reflection problem due to the enclosure

walls. In addition, the total power radiated by the EUT and the maximum

power density produced by it at a specific point of space can all be

determined by this method.

Alternatively, placing the unknown EUT at the center of a doubly loaded

loop antenna in a given plane (say, the xy plane) and then rotating the

loops in two extra orthogonal orientations (the yz and zx planes) will

realize the same objective for determining the low-frequency magnetic field

and total power radiated by the EUT [11] as in Method REOl, but on a much

firmer basis.

For determining the EUT's susceptibility to radiated magnetic field,

radiated electric field, or both, the TEM cell method can also be applied

advantageously. When a TEM cell is fed from one end and is terminated with

a matched load on the other end, a plane wave is generated inside the cell.

This method can be used to replace Method RS04, where a parallel -plate

transmission line was specified for this measurement. A parallel-plate line

is susceptible through its side opening, however, to other potential

interferences. Furthermore, because only two orientations were recommended

in Method RS04, its measurements may not be as complete for assessing the

EUT's susceptibility characteristics as the TEM cell method.

When the receiving port of a TEM cell remains open, a field environment

with dominant electric field but negligible magnetic field can be generated

near the center of the cell [12]. This arrangement is suitable for testing

the EUT's susceptibility to electric fields and thus can be used to replace

Method RS03. On the other hand, if the receiving port of a TEM cell is

shorted, a different field environment with dominant magnetic field but

negligible electric field can be created [12] to replace Methods RSOl and

RS02 for testing the EUT's susceptibility to magnetic fields. These two

methods apply only to lower frequencies below the cut-off frequency of a TEM

cell determined by its size. Related issues such as measurement

uncertainties and perturbation effects due to the presence of EUT inside the

TEM cell are also discussed in these alternative methods . Thus , in lowfrequency emission and susceptibility measurements, the capabilities and

facilities at NIST are more than adequate to meet the industrial need.

To verify the suggested alternative methods for measurements, we should

perhaps do more work by selecting a known device as our EUT to be measured

by these alternative methods for both emissions and susceptibility (or

immunity) , and then compare the results with those obtained according to

MIL-STD-462. A meaningful assessment may then be made in a quantitative

manner

.

22
For testing EUT's susceptibility to electric fields at higher

frequencies, as in Method RS03 , a better facility such as an anechoic

chamber is suitable with much stronger technical justification. The chamber

at NIST designed for the frequency range of 200 MHz to 40 GHz can be used

for this purpose [13] . Characteristics of this chamber including quality of

the fields generated at the test zone by standard antennas, uncertainty

estimates, and near-field corrections have all been analyzed.

Part 15 of the FCC standards specifies that a sensing dipole antenna be

placed at the respective distances of 30 m and 3 m away from Class A and

Class B computing devices for measuring the electric field leakage from

these devices at three different frequency bands. When these distances are

not met because of practical limitations, determination of electric fields

from measurements at a shorter distance (or a longer distance up to 30 m)

and based on the inverse -distance relationship was recommended. Again, a

shorter distance may put the sensing dipole within the near- field range

(dependent on the actual frequency) from the emitting computing devices.

Under this condition, the inverse -distance relationship will not apply, and

the derived electric field will not accurately represent the actual

emission, thus resulting in errors. This same comment applies to some of

the ANSI standards as well.

Generally speaking, more reliable measurements (TEM cell or anechoic

chamber depending on the size of an EUT and frequency) are required for

determining more accurately the emission and immunity of electronic

components and subsystems. Therefore, understanding and physical

interpretations of the measured data under different conditions are also

important for the final EMC analysis.

b. Shielded Enclosure

Shielded enclosures of rectangular cross section are frequently

recommended in the existing standards such as in Method RE03 and ANSI C63.4

for measuring the emissions from an EUT. The same recommendation has also

been made for measuring rf susceptibility of equipment in order to generate

very high fields inside the enclosure without causing interference to nearby

equipment. This technique, while good from the security point of view, has

caused major disagreements among the users. The main reason is that the

direct-path radiation from an EUT placed inside the enclosure is added

vectorially to the reflections from enclosure walls . The final vector sum

may be significantly different from the direct-path result, depending on the

phase differences resulting from different path lengths . The deviation

between the combined vector sum and the direct-path result may be as large

as 40 dB. A small change in the distance between an EUT and a sensor can

result in a large difference in the final measured result. After this

fundamental deficiency was discovered, using rf absorbing materials inside

the enclosure was suggested as a remedial means for reducing the effect of

reflection. While this remedy is proven effective in many cases, it still

cannot yield repeatable measurement results within a small tolerance because

the size (frequency dependent) and number of absorbing panels and their

exact locations inside the enclosure result in different effects. In

addition, the metal shielded enclosure also behaves as a rectangular cavity

with a high quality factor (Q)

Strong field amplification occurs at

different resonant frequencies, making comparison of the measurement results

meaningless

23
A serious assessment of the measurement error bound incurred in a

typical shielded enclosure as specified in MIL-STD-462 was made by NIST [14]

together with a suggestion of alternative techniques for using the same

enclosure [15]. A more viable technique, based on theoretical

understanding, would be the use of a reverberating chamber. Such chambers

have been extensively investigated by NIST [13, 16, 17]. All the

advantages associated with the shielded chamber, such as security

considerations and generation of high fields inside the enclosure without

causing interferences to exterior equipment, are retained. An existing

conventional shielded enclosure can be converted to a reverberating chamber

with the addition of extra parts and devices such as a mode stirrer, a

motor, and other necessary items.

With the size of 2.74 m x 3.05 m x 4.57 m, our reverberating chamber

can be operated at a frequency as low as 200 MHz . The measurement

uncertainty is about 5 to 7 dB, which, although still high, represents a

significant improvement over the conventional shielded enclosure. Results

of rf susceptibility for various components and systems measured inside the

NIST reverberating chamber have been found comparable, within a certain

difference, to that obtained inside an anechoic chamber. The difference is

attributed mainly to the EUT's gain as a receiving antenna. The input power

requirement for the reverberating chamber is, however, much less than that

for the anechoic chamber to produce the same testing field. Comparison of

our measured results with that obtained from other reverberating chamber of

different sizes has also been made and found to be in good agreement. This

chamber offers a good NIST facility for meeting the requirement of highfrequency susceptibility testing. We should extend our research work in

this area toward much lower- frequency applications in the near future.

c. Site Attenuation

Many measurements in the current standards such as Method RE03 in MILSTD-462, FCC Part 15, and ANSI C63.4 require a good ground screen for

performing open-field tests. The quality of a ground screen may be

characterized by a factor called site attenuation, which is based on the

concept of minimum insertion loss. However, the mathematical definitions

for site attenuation as used by the FCC, International Electrotechnical

Commission, and NIST are different, depending on the condition assumed in

the derivation [13]. Practically, the ground must be well constructed with

a large size so that it may approach the ideal case where the amplitude of

the ground reflection coefficient is 1 for both horizontal and vertical

polarizations as is normally assumed in theoretical formulations. The often

used simple roof-top space without the reinforcement of additional metal

screens may not be adequate to meet this condition, even though providing a

metal screen is not mandatory in the FCC standard. A method of measurement

yielding good results on site attenuation as suggested by NIST can be found

in the literature [18]. Measured results have been found to be in good

agreement with theoretical results. The one used at NIST is a 30 m x 60 m

wire mesh ground. The frequency range is approximately from 30 kHz to 1

GHz. This ground, as well as a set of well characterized dipoles with

adjustable lengths and other ancillary equipment, represents a good reliable

measurement facility. It has been frequently used for calibrating antennas

and measuring emissions from unknown sources by our customers or by

ourselves

.

24
The quality of the open site used for measurements is also critical.

It should be beneficial to the EMC community if an existing site, after a

thorough evaluation and characterization, is designated as the standard

site. A new site to be built by others can be evaluated by a standard

method and its characteristics compared with those of the standard site.

This exercise will enhance measurement repeatability.

d. Far-Field vs. Near-Field Conditions

We already mentioned some potential errors which may occur for certain

low-frequency cases when an inverse -distance relationship is applied, in

compliance with the FCC Part 15 requirements, for converting the measured

electric field at a shorter distance from the computing devices to a

distance of 3 m. In addition, the antenna factor provided by antenna

manufacturers to be used in the measurement is exclusively calibrated under

the far- field condition. Since the antenna characteristics differ in farfield and near- field regions, a direct application of the far- field antenna

calibration curve to the measurement of emitted fields in a near- field

situation will also produce some errors in interpreting the measurement

results . Thus , a correction factor based on measurements , computations , or

both should be included in the actual measurements to compensate for the

difference. Some preliminary work in this area at NIST has already begun

[19]. More systematic analyses and measurements for calibrating antennas in

a near-field environment should also be done. Furthermore, in the

computation of antenna factor for a linear dipole antenna, the sinusoidal

current distribution on the dipole has normally been assumed, for

simplicity, in the EMC community. Strictly speaking, this assumption is

accurate only for an infinitely thin dipole with the dipole length no more

than a half wavelength with respect to the frequency of interest. For a

thicker or a longer dipole, a more realistic current distribution should be

used to yield better results for the antenna factor [20]Even though this

consideration may only yield a minor improvement in accuracy, some work in

this area together with the effect of mutual impedances between dipoles on

the current distribution may be carried out for making a quantitative

analysis

Other commonly used antennas in the dipole family such as top -loaded

antennas and bow-tie antennas should also be analyzed more carefully based

on good theoretical models before a calibration curve is generated for

application.

In general, better low-frequency antenna calibrations could be achieved

by taking the above factors into consideration.

e. Shielding Effectiveness

To achieve EMC an extra shielding material is often provided to protect

the vulnerable parts in a system. The shielding properties of a material

with respect to the radiated electric and magnetic fields are dependent

strongly on frequency, space, and polarization of the interfering fields.

The measured results on shielding materials also depend on the specific

setup, instrumentation, and type of antennas used in the experiment [5,6].

Because of a lack of thorough understanding of the coupling theory, many

questionable measurements recommended to meet the requirements in MIL- STD285 have been suggested and included in the standards to yield erroneous

information on shielding effectiveness (SE)

In fact, consistent results

25
based on those recommended measurements have never been obtained. Thus, the

true SE of many commercial materials was not positively determined by a

reliable method of measurement until 1989, when ASTM formally adopted the

method of measuring SEs of planar materials as proposed by NIST [21]

.

This

method is based on the far- field concept. Related background studies from

both theoretical and experimental considerations are found elsewhere [5].

Studies for evaluating the SE of materials in a near- field environment

should also be done with the objective of establishing another measurement

standard under this particular situation. Measurements, based on

theoretical understanding, for evaluating the SE of containers or enclosures

to complement IEEE Standard 299-1969 and the SE of gaskets have not been

available. Further study in these areas by NIST is thus desirable.

f. Probe Requirements

To verify the emission limits as required in many standards, different

antennas for different frequency bands have been recommended for

measurement. Some of these antennas are physically large. The true field

structure appearing at a particular region in space as emitted from an

unknown EUT is often disturbed by the presence of such a large measuring

antenna. This will cause inaccuracy in the measurement. Thus, a broadband

antenna with a much smaller physical size (a probe) , together with an

optical sensing system to minimize the disturbance would be ideal. That is

why NIST has developed a few broadband probes for this purpose [22-24]

.

The

latest probe model has its dipole length as small as 2 mm with a theoretical

upper frequency range to 70 GHz. Dynamic range and the field environment in

which the probe may be calibrated are the ultimate limits for probes in the

order of this small size. The capability of developing broadband probes at

NIST is outstanding. Application of these probes to emission measurements

as required in the existing standards will yield more accurate results.

g. Electrostatic Discharges

Components and subsystems in many complicated systems perform their

command and control functions by computers. Since these computers use lowpower semiconductor chips and other sensitive electronics, they are

susceptible to electrostatic discharges (ESD) created by contacts and

friction between two materials of different triboelectric ranks. While

problems due to ESDs by direct contact have been partially eliminated

through grounding and bonding techniques, the effects of indirect ESDs

(radiation of electric and magnetic fields through air discharges) have only

been noted recently [25,26]. Since the rise time of a discharged current

waveform can be very fast, in the order of fractions of a nanosecond or

smaller, depending on the actual environment and discharging voltage, this

current waveform contains a very broad spectrum and radiates fields of

significant strengths. For example, the radiated electric field at a short

distance away from the ESD source can be as high as a few hundred volts per

meter or higher. Although these fields are transient (occurring in a brief

duration) , they can cause temporary upsets , malfunctions , or other adverse

EMI effects on the highly sensitive electronics involved. For this reason,

ESD tests are required in the SAE standard for automobiles and aircraft. A

direct-contact test by a commercially available ESD simulator was

specifically recommended in SAE Method J1113. It requires, however, a clean

metal surface of EUT for the ESD simulator to be effective. Discharging to

a painted or coated surface often produces unpredictable results. Also,

this direct-contact method cannot be used on hard-to-reach areas. For these

26
reasons, one automobile company has decided in favor of the fixed gap airdischarge method for its validation testing of components [27]. This

practice is likely to be included in the future revised SAE standard.

However, a caution should be noted. Since the ESD-radiated fields are

broadband, wideband equipment will be required for measuring such signals

with any physical meaning. Measurements with inexpensive narrowband

equipment will not represent the true waveform and may result in errors

NIST has made an initial contribution in this area of measuring

simultaneously the fast-rise current waveforms and radiated transient

electric fields due to ESDs [25,26]. Its recommendations have been included

in "Guide on Electrostatic Discharge from Personnel and Small Mobile

Furnishings," issued by IEEE Surge Protective Devices Committee (SPD Working

Group 3.6.8)

A new ESD standard is being developed in Europe and may have

significant impacts on future U. S. exports of electronic devices and

computers to Europe

h. Bulk Current Injection

A number of radiated susceptibility tests in existing standards,

especially that for aircraft equipment, require generation of high electric

fields at various frequencies in the open environment. This method may not

be practical because it conflicts with the FCC's compliance rule.

Consequently, many investigators have suggested that the current- inj ection

method be used to replace it [28, 29], with the hope that this method may be

established as an alternative and equivalent evaluation. This method

involves injecting currents directly into one or more wires within a bundle.

These current magnitudes can be substantial in the actual susceptibility

test. It would otherwise require very high radiated fields to induce the

same magnitude of currents on those particular wires. Indeed, if it were

proven equivalent to the conventional radiated susceptibility test, it would

be very advantageous because it can be performed in a laboratory

environment, and the injection current can be made as high as the

application problem at hand demands. However, preliminary measurement

results from a recent study at NIST indicate otherwise [30]Calculations

based on a related theoretical study of this topic at NIST also show

significant difference [31]: current distributions on the individual wires

in a wire bundle excited by injection are not the same as those excited by

radiation. In fact, the difference in test results by the two methods for

the same wires (in number and lengths) can be substantial, ±30 dB or more.

The difference in result is small only when electrically short wires are

involved. However, this may not be the case in practice. Furthermore, the

system under test may be nonlinear. Higher current injection does not

always produce proportionally more interference. Therefore, current

injection has not been able, in general, to yield repeatable measurement

data. At a minimum, a serious study of this topic to provide a more

meaningful engineering interpretation of the measurement data is desired

before it is considered as a standard. Good research results from a study

at NIST will benefit the aerospace and EMP- related industry.

4. Conclusions and Suggestions

A review of many EMC -related U. S. standards, either being enforced by

government agencies or recommended by voluntary organizations, has been

presented. The highlights and unique features for each standard under

27
review have been outlined and commented on. Deficiencies and potential

problems associated with some of these standards have been pointed out from

technical considerations. Alternative but better measurement techniques,

whenever available, have been suggested. Existing measurement capabilities

at NIST are generally adequate to meet the current industrial need. Eight

areas -- characterization of EM environment for frequencies above 1 GHz,

experimental verification of loop -antenna method for low-frequency testing

of radiated magnetic fields with a known EUT, extending application of

reverberating chamber to susceptibility testing at much lower frequencies,

establishing a standard open-field site for intercomparison, calibration of

dipole antennas in a near- field environment, more accurate current

distribution on dipoles and mutual -coupling effect, determination of the

shielding properties of materials based on near- field simulation and that of

containers and gaskets, and validity of the current- inj ection method being

considered in the aircraft industry as an alternative method for EMC tests - are specifically mentioned as possible future study topics. Since many

recent electronic products involve digital systems, more attention should

also be paid to the establishment of time -domain measurement methods and

facilities with broadband applications to pulsed EMI problems. In addition,

while accurate measurements of emissions and immunity of small devices or

subsystems are important, those for large products and systems such as

vehicles and aircraft, especially when the required testing field is very

high, should also be under our consideration for possible future work.

5. References

[1] Osburn, J.D.M. Military Electromagnetic Compatibility Standards of the

United States, vol. 11, Interference Control Technologies, Inc., 1988;

Gainesville, VA.

[2] Eckert, J.K. Commercial EMC Standards of the United States, vol. 9,

Interference control Technologies, Inc., 1988; Gainesville, VA.

[3] Straus, I. FCC gives nod to ANSI test methods. Compliance Engineering,

Spring, 1991.

[4] FCC's adoption of ANSI test methods. Compliance Engineering, Fall,

1991.

[5] Wilson, P.F; Ma, M.T. ; Adams, J.W. Techniques for measuring the

electromagnetic shielding effectiveness of materials. Part I -- farfield source simulation. IEEE Trans. Electromag. Compat. , vol. 30,

no. 3, 239-250, August, 1988.

[6] Wilson, P.F.; Ma, M.T. Techniques for measuring the electromagnetic

shielding effectiveness of materials. Part II -- near- field source

simulation. IEEE Trans. Electromag. Compat., vol, 30, no. 3, 251-259,

August, 1988.

[7] Adams, J.W.; Vanzura, E.J. Shielding effectiveness measurements of

plastics. Nat. Bur. Stand. (U.S.) NBSIR 85-3035; 1986 January.

[8] von Achen, W. The Apache helicopter: an EMI case history. Compliance

Engineering, Fall, 1991.

28
[9]

Ma, M.T. ; Koepke , G.H. A method to quantify the radiation

characteristics of an unknown interference source. Nat. Bur. Stand.

(U.S.) Tech. Note 1059; 1982 October.

[10] Koepke, G.H. ; Ma, M.T. ; Bensema, W.D. Implementation of an automated

system for measuring radiated emissions using a TEM cell. IEEE Trans.

Instrum. & Meas . , vol. 38, no. 2, 473-479, April, 1989.

[11] Kanda, M. ; Hill, D.A. A three-loop method for determining the

radiation characteristics of an electrically small source. To be

published by IEEE Trans. Electromag. Compat.

[12] Ma, M.T. ; Larsen, E.B. ; Crawford, M.L. Electromagnetic fields with

arbitrary wave impedances generated inside a TEM cell. IEEE Trans.

Electromag. Compat., vol. 33, no. 4, 358-362, November, 1991.

[13] Ma, M.T. ; Kanda, M. ; Ed. Electromagnetic compatibility and

interference metrology. Nat. Bur. Stand. (U.S.) Tech. Note 1099; 1986

July.

[14] Cruz, J.E.; Larsen, E.B. Assessment of errors for MIL-STD-461/462

Nat. Bur. Stand. (U.S.) Tech. Note 1300; 1986 October.

[15] Cruz, J.E.; Larsen, E.B. Alternative techniques for some typical MILSTD-461/462 types of measurements. Nat. Bur. Stand. (U.S.) Tech. Note

1320; 1989 March.

[16] Crawford, M.L. Evaluation of a reverberating chamber facility for

performing EM radiated field susceptibility measurements. Nat. Bur.

Stand. (U.S.) NBSIR 81-1638; 1981 February.

[17] Ma, M.T. Understanding reverberating chambers as an alternative

facility for EMC testing. J. Electromag. Waves & Appl., vol 2, no.

3/4, 339-351, 1988.

[18] FitzGerrell, R.G. Site attenuation. Nat. Bur. Stand. (U.S.) Tech.

Note 1089; 1985 November.

[19] Randa, J.P. Correction factor for non-plane -wave incident field in

monopole calibrations. To be published by IEEE Trans. Electromag.

Compat

[20] King, R.W.P.; Wu, T.T. Currents, charges, and near fields of

cylindrical antennas. Radio Sci. vol. 69D, no. 3, 429-446, March,

1965.

[21] ASTM D 4935-89. Standard test method for measuring electromagnetic

shielding effectiveness of planar materials. ASTM, 1916 Race St.,

Philadelphia, PA 19103.

[22] Kanda, M. ; Ries , F.X. A broadband isotropic real-time electric- field

sensor (BIRES) using resistively loaded dipoles. IEEE Trans.

Electromag. Compat., vol. 23, no. 3, 122-132, August, 1981.

29
[23] Randa, J.P.; Kanda, M. ; Orr, R.D. Thermo -optic designs for

electromagetic-field probes for microwaves and millimeter waves, IEEE

Trans. Electromag. Compat. , vol. 33, no. 3, 205-214, August, 1991.

[24] Randa, J.P.; Kanda, M. ; Orr, R.D. Resistively- tapered-dipole electricfield probes up to 40 GHz. IEEE Int. Symp. on EMC; 265-266, August,

1991; Cherry Hill, NJ

.

[25] Wilson, P.F.; Ma, M.T. Electromagnetic fields radiated from

electrostatic discharges -- theory and experiment. Nat. Bur. Stand.

(U.S.) Tech. Note 1314; 1988 February.

[26] Wilson, P.F.; Ma, M.T. Fields radiated by electrostatic discharges.

IEEE Trans. Electromag. Compat., vol. 33, no. 1, 10-18, February, 1991.

[27] Sperber, W.M.

;

Minnich, K.J. Test procedure and specifications for

component susceptibility to electrostatic discharges. IEEE Int. Symp.

on EMC; 190-195, August, 1988; Seattle, WA.

[28] Carter, N.J. The development of a revised susceptibility test for

avionic equipment. Int. Conf. on EMC, 241-255, 1982; Surrey.

[29] Bull, D.A.

;

Carter, N.J. Evaluation of a revised rf susceptibility

test for aircraft equipment. Int. Conf. on EMC, 257-271, 1982; Surrey.

[30] Adams, J.W.; Cruz, J.E.; Melquist, D. Comparison of currents induced

by radiation and injection. To be published by IEEE Trans. Electromag.

Compat

.

[31] Hill, D.A. Comparison of currents induced on multiconductor

transmission lines by radiation and injection. Submitted to IEEE

Trans. Electromag. Compat.

30
BL-114A U.S. DEPARTMENT OF COMMERCE

(5-90) NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

ADMAN 15.01

BIBLIOGRAPHIC DATA SHEET

1. PUBUCATION OR REPORT NUMBER

NlSm 3989

2. PERFORMING ORctANIZATION REPORT NUMBER

B92-0147

3. PUBUCATION DATE

May 1992

4. TITLE AND SUBTITLE

EMC Standards and Regulations: A Brief Review

S. AUTHOR(S)

M.T. Ma

6. PERFORMING ORGANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BOULDER, COLORADO 80303-3328

7. CONTRACT/GRANT NUMBER

8. TYPE OF REPORT AND PERIOD COVERED

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (STREET, C4TY, STATE, ZIP)

10.

SUPPLEMENTARY NOTES

11.

ABSTRACT (A 20O-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIF1CAMT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBUOGRAPtlY OR

LITERATURE SURVEY, MENTION IT HERE.)

Important current regulations and standards regarding electromagn^c compatibility (EMC) measurements are reviewed. These

regulations and standards have been eidier enforced by U.S. government agencies such as the Federal Communications

Commitssion and Department of Defense, or incorporated in voluntary industrial practice. The specific methods and

configurations of measurement required in some of these standards are assessed from a technical basis to see whether or not

they are adequate and ^propriate. Technical deficiencicies and potential problems, if any, are pointed out together with

recommendations of alternative and b^ter methods of measurements. Concurrently, the EMC measurement c^ability at the

National Institute of Standards and Technology is evaluated and appraised for the purpose of planning new metrology activities or programs responsive to the needs of U.S. industry.

12.

KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITALIZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

electric field; electromagnetics; EMC; EMI; emission; magn^c field; measurement methods; requirement; regulation; review;

standards; suscq)tibility

13. AVAILABILITY 14. NUMBER OF PRINTED PAGES

X UNUMITEO

34 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS).

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WASHINGTON, DC 20402. AO 3

-JL ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGFIELD, VA 22161. ELECTRONIC FORM
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