ASTM E1851-21

Standard Test Method for Electromagnetic Shielding Effectiveness of Durable Rigid Wall Relocatable Structures

SIGNIFICANCE AND USE
5.1 This standard provides measurement procedures for determining the electromagnetic shielding effectiveness of durable rigid wall relocatable shielded enclosures. This standard specifies a method for comparing the shielded enclosure performance of structures provided by different suppliers. In addition, this standard is written to minimize variations in measured shielding effectiveness at a given frequency and test point regardless of test personnel, equipment, and test site. Therefore, the shielding effectiveness of a durable rigid wall relocatable shielded enclosure of any size from any supplier can be determined. This standard specifies a minimum set of measurements at a given frequency and a minimum set of frequencies to determine shielding effectiveness.  
5.2 Source Fields—Performance of a shielded enclosure is to be assessed for two source fields: magnetic and plane wave.  
5.2.1 Magnetic Field Measurements—The attenuation provided by a shielded enclosure is assessed by using a local source to generate the near field. The magnetic field measurements are specified for two narrow frequency bands: 140 kHz to 160 kHz and 14 MHz to 16 MHz.  
5.2.2 Plane Wave Measurements—The attenuation provided by a shielded enclosure is assessed by using a locally generated distant source or plane wave field. The plane wave measurements are specified for three narrow frequency bands: 300 MHz to 500 MHz, 900 MHz to 1000 MHz, and 8.5 GHz to 10.5 GHz.
SCOPE
1.1 This test method covers the determination of the electromagnetic shielding effectiveness of durable relocatable shielded enclosures.  
1.1.1 The intended application of this test method is for virgin shielded enclosures that do not have any equipment or equipment racks. It is recommended that tests be conducted before the interior finish work begins. However, the shield assembly including all enclosure penetrations shall be completed and required penetration protection devices shall be installed in accordance with the design specification. The test method can also be used on existing shielded enclosures after repair work is done to verify workmanship, but it may be necessary to remove equipment or equipment racks to gain access to a test area.  
1.1.2 The test procedures delineated in this document are comprehensive and may require several days to complete for a room-size shielded enclosure. A user can apply this test method for a first article test that requires proof of concept and validation of design and fabrication technique. Appendix X2 provides guidance on choosing test points so shielding effectiveness tests on a room-size shielded enclosure may be completed in about one-half day for which it applies to shielded enclosures coming off an assembly line.  
1.2 This test method is for use in the following frequency ranges: 140 kHz to 160 kHz, 14 MHz to 16 MHz, 300 MHz to 500 MHz, 900 MHz to 1000 MHz, and 8.5 GHz to 10.5 GHz. Specific test frequencies within these ranges are required (see 11.1.1 and 11.2.1). Additional measurements in the range of 10 kHz to 10.5 GHz may be performed. For specific applications, the frequency range may be extended from 50 Hz to 40 GHz. Appendix X1 provides guidance on selecting measurement frequencies.  
1.3 This test method is not applicable to individual components such as separate walls, floors, ceilings, or shielded racks.  
1.4 This standard may involve hazardous materials, operations, equipment, or any combination.  
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7...

General Information

• Status: Published
• Publication Date: 31-Jan-2021
• ICS: 13.280 - Radiation protection
• Technical Committee: E06 - Performance of Buildings
• Drafting Committee: E06.53 - Materials and Processes for Durable Rigidwall Relocatable Structures

Relations

• Refers: ASTM E1749-18 - Standard Terminology Relating to Rigid Wall Relocatable Shelters
• Effective Date: 01-Oct-2018
• Refers: ASTM E631-15 - Standard Terminology of Building Constructions
• Effective Date: 01-Mar-2015
• Refers: ASTM E631-14 - Standard Terminology of Building Constructions
• Effective Date: 01-Nov-2014
• Refers: ASTM E1749-10 - Standard Terminology Relating to Rigid Wall Relocatable Shelters
• Effective Date: 01-Nov-2010
• Refers: ASTM E631-06 - Standard Terminology of Building Constructions
• Effective Date: 01-Jun-2006
• Refers: ASTM E1749-05 - Standard Terminology Relating to Rigid Wall Relocatable Shelters
• Effective Date: 01-Oct-2005
• Refers: ASTM E631-93a(1998)e1 - Standard Terminology of Building Constructions
• Effective Date: 28-Jul-2000
• Refers: ASTM E1749-00 - Standard Terminology Relating to Rigid Wall Relocatable Shelters
• Effective Date: 10-Apr-2000

Overview

ASTM E1851-21: Standard Test Method for Electromagnetic Shielding Effectiveness of Durable Rigid Wall Relocatable Structures provides a standardized approach for objectively measuring and comparing the electromagnetic shielding effectiveness (SE) of durable, rigid wall relocatable shielded enclosures. Developed by ASTM International, this method facilitates consistent evaluation of the shielding performance of enclosures from different manufacturers, ensuring that the results are reliable and repeatable regardless of personnel, equipment, or test location.

This test method is applicable to enclosures designed to prevent electromagnetic interference (EMI) and is highly relevant to sectors that require protection of sensitive electronic equipment or data from external electromagnetic fields, such as defense, communications, data centers, healthcare, and critical infrastructure.

Key Topics

• Measurement Procedures
  The standard details specific procedures for evaluating shielding effectiveness across a minimum set of frequencies and source types (magnetic field and plane wave).

• Frequency Ranges Covered

  • Magnetic field measurements: 140 kHz - 160 kHz and 14 MHz - 16 MHz
  • Plane wave measurements: 300 MHz - 500 MHz, 900 MHz - 1000 MHz, and 8.5 GHz - 10.5 GHz
    Additional testing may be done from 10 kHz to 10.5 GHz, with the possibility to extend to 50 Hz - 40 GHz for specific applications.

• Repeatability and Comparison
  The procedure is structured to reduce measurement variability, allowing direct comparison between enclosures, regardless of supplier or facility.

• Test Situations

  • For new (virgin) enclosures without installed equipment, testing is recommended before interior finish work begins.
  • After repairs on existing structures, the standard can validate workmanship and verify enclosure integrity.

• Test Scope
  The method is not applicable to individual components such as single panels, floors, ceilings, or racks; it is intended for fully assembled enclosures.

• Safety and Compliance Users of the standard must ensure all safety, health, and environmental regulations are addressed when conducting measurements.

Applications

• Quality Assurance in Manufacturing
  Manufacturers use ASTM E1851-21 as a first article test or proof-of-concept to validate design and fabrication effectiveness before shipment or deployment.

• Field Verification and Maintenance
  Facility managers or service providers utilize this standard to test enclosures after repairs or modifications, ensuring maintained shielding performance over time.

• Supplier Benchmarking
  Organizations can directly compare the electromagnetic shielding performance of enclosures from different vendors using uniform measurement procedures.

• Regulatory and Security Compliance
  The standard supports industries with regulatory or operational requirements for EMI shielding, such as military sites, secure communication hubs, and laboratories handling sensitive measurements.

• Product Development and R&D
  Organizations involved in developing next-generation shielded enclosures employ this method for evaluating design iterations and achieving optimal EMI protection.

Related Standards

• ASTM E631: Terminology of Building Constructions
  Provides foundational definitions for terms used in this test methodology.

• ASTM E1749: Terminology Relating to Rigid Wall Relocatable Shelters
  Offers terminology specific to relocatable shelter applications.

• IEEE Std 299-1997: Standard Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures
  An IEEE standard referenced for its complementary test methods.

• IEEE Std C95.1-1991: Safety Levels for Exposure to Radio Frequency Fields
  Used to ensure safety during electromagnetic field exposure in test environments.

• MIL-STD-188-125: HEMP Protection for Ground Based C I Facilities
  Addresses specific military needs for electromagnetic pulse (EMP) protection.

• OSHA 29 CFR 1910: Occupational Safety and Health Standards
  Cited to ensure safe operation during testing.

Using ASTM E1851-21 ensures robust, comparable, and repeatable measurement of electromagnetic shielding effectiveness, supporting manufacturers, facility managers, and specifiers in their efforts to ensure EMI protection and compliance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:E1851 −21
Standard Test Method for
Electromagnetic Shielding Effectiveness of Durable Rigid
Wall Relocatable Structures
This standard is issued under the fixed designation E1851; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope the frequency range may be extended from 50 Hz to 40 GHz.
Appendix X1 provides guidance on selecting measurement
1.1 This test method covers the determination of the elec-
frequencies.
tromagnetic shielding effectiveness of durable relocatable
shielded enclosures. 1.3 This test method is not applicable to individual compo-
1.1.1 The intended application of this test method is for nents such as separate walls, floors, ceilings, or shielded racks.
virgin shielded enclosures that do not have any equipment or
1.4 This standard may involve hazardous materials,
equipment racks. It is recommended that tests be conducted
operations, equipment, or any combination.
before the interior finish work begins. However, the shield
1.5 The values stated in SI units are to be regarded as
assembly including all enclosure penetrations shall be com-
standard. The values given in parentheses after SI units are
pleted and required penetration protection devices shall be
provided for information only and are not considered standard.
installed in accordance with the design specification. The test
method can also be used on existing shielded enclosures after 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
repair work is done to verify workmanship, but it may be
necessary to remove equipment or equipment racks to gain responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
access to a test area.
1.1.2 The test procedures delineated in this document are mine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accor-
comprehensive and may require several days to complete for a
dance with internationally recognized principles on standard-
room-sizeshieldedenclosure.Ausercanapplythistestmethod
for a first article test that requires proof of concept and ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
validation of design and fabrication technique. Appendix X2
provides guidance on choosing test points so shielding effec- mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
tiveness tests on a room-size shielded enclosure may be
completed in about one-half day for which it applies to
2. Referenced Documents
shielded enclosures coming off an assembly line.
2.1 ASTM Standards:
1.2 This test method is for use in the following frequency
E631Terminology of Building Constructions
ranges: 140kHz to 160kHz, 14MHz to 16 MHz, 300MHz to
E1749Terminology Relating to Rigid Wall Relocatable
500 MHz, 900MHz to 1000 MHz, and 8.5GHz to 10.5GHz.
Shelters
Specific test frequencies within these ranges are required (see
2.2 IEEE Standards:
11.1.1and11.2.1).Additionalmeasurementsintherangeof10
IEEE Std299-1997IEEE Standard Method for Measuring
kHz to 10.5 GHz may be performed. For specific applications,
theEffectivenessofElectromagneticShieldingEnclosures
1 2
This test method is under the jurisdiction of ASTM Committee E06 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Performance of Buildings and is the direct responsibility of Subcommittee E06.53 contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
on Materials and Processes for Durable Rigidwall Relocatable Structures. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Feb. 1, 2021. Published February 2021. Originally the ASTM website.
approved in 1997. Last previous edition approved in 2015 as E1851-15. DOI: Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
10.1520/E1851-21. 445 Hoes Ln., Piscataway, NJ 08854-4141, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1851−21
TABLE 1 Test Frequencies and Test Configurations
measured shielding effectiveness at a given frequency and test
Corresponding Test point regardless of test personnel, equipment, and test site.
Nominal Test Frequency
Configuration
Therefore, the shielding effectiveness of a durable rigid wall
150 kHz and 14 MHz Fig. 1
relocatable shielded enclosure of any size from any supplier
400 MHz, 1000 MHz, and 10 GHz Fig. 2
can be determined. This standard specifies a minimum set of
measurements at a given frequency and a minimum set of
frequencies to determine shielding effectiveness.
IEEEStdC95.1-1991 IEEEStandardforSafetyLevelswith
Respect to Human Exposure to Radio Frequency Electro- 5.2 Source Fields—Performance of a shielded enclosure is
magnetic Fields, 3 kHz to 300 GHz to be assessed for two source fields: magnetic and plane wave.
2.3 Military Standard: 5.2.1 Magnetic Field Measurements—The attenuation pro-
vided by a shielded enclosure is assessed by using a local
MIL-STD-188-125 High Altitude Electromagnetic Pulse
(HEMP) Protection for Ground Based C I Facilities Per- source to generate the near field. The magnetic field measure-
ments are specified for two narrow frequency bands: 140kHz
forming Critical, Time-Urgent Missions
to 160 kHz and 14MHz to 16 MHz.
2.4 OSHA Standard:
5.2.2 Plane Wave Measurements—The attenuation provided
OSHARegulation,29CFR1910,DepartmentofLabor,July
byashieldedenclosureisassessedbyusingalocallygenerated
distant source or plane wave field. The plane wave measure-
3. Terminology
ments are specified for three narrow frequency bands:
300MHzto500MHz,900MHzto1000MHz,and8.5GHzto
3.1 Definitions:
10.5 GHz.
3.1.1 For definitions of general terms related to building
construction used in this test method, refer to Terminology
6. Interferences
E631, and for general terms related to rigid wall relocatable
6.1 Interference with Electronic Equipment—Care shall be
shelters, refer to Terminology E1749.
taken to avoid interference with other electronic equipment
4. Summary of Test Method operating in the vicinity.
4.1 Test Configuration—A transmitting antenna is con-
6.2 Operational Impact Analysis and Risk—The electro-
nected to an electromagnetic source set to a specific frequency magnetic barrier must remain intact during the shielding
and amplitude. A receiving antenna is placed a specified
effectiveness measurement sequence, and use of electrically
distance from the transmitting antenna, and the received noisy equipment must be restricted. Therefore, construction
electromagnetic field level is recorded as a reference or
activity or unusual operations (facility modification or mainte-
calibration measurement. The transmitting antenna and elec-
nance) may be affected. Radiated signal levels should present
tromagnetic source are placed outside the shielded enclosure.
no hazard to equipment, but frequency adjustments may be
Thereceivingantennaandassociatedtestequipmentareplaced
required to avoid self interference or interference with nearby
inside the shielded enclosure. The transmitting and receiving
facilities. Record the actual test frequencies. Normal electrical
antenna’s separation, frequency, and amplitude are the refer-
safety precautions apply.
ence measurements. The transmitting and receiving antennas
7. Apparatus
are at the same height for a given test point. The received
electromagneticfieldlevelisrecordedasthetestmeasurement. 7.1 The required apparatus is identified in Table 2. Choose
Theratioofthetestmeasurementtothereferencemeasurement
test equipment that provides a dynamic range of at least 10 dB
is the electromagnetic shielding effectiveness of the shielded (20 dB is preferable [see Note 1]) in excess of the shielding
structure at the measurement location and frequency. The
effectiveness requirement at the test frequency.
logarithm of this ratio is typically used in expressing the
NOTE 1—20 dB of dynamic range makes the test easier to perform by
shielding effectiveness in decibels.
less experienced personnel. The standard uses a minimum of 10 dB
because it offers a lower cost solution to testing durable rigid wall
4.2 Test Frequencies—Asummary of nominal test frequen-
relocatablestructures.Iftheexistingtestequipmenthas20dBofdynamic
cies and corresponding test configurations is shown in Table 1.
range then 20 dB of dynamic range should be used. It makes the hot spots
standoutmoreclearlyfromthebackgroundnoiseontheLCDdisplayson
5. Significance and Use
spectrum analyzers.
5.1 This standard provides measurement procedures for
8. Hazards
determining the electromagnetic shielding effectiveness of
8.1 For human exposure to electromagnetic energy in con-
durable rigid wall relocatable shielded enclosures. This stan-
trolled environments, the maximum permissible exposure to
dard specifies a method for comparing the shielded enclosure
electric and magnetic field strengths shall be minimized to the
performance of structures provided by different suppliers. In
maximum extent possible. Acceptable levels can be found in
addition, this standard is written to minimize variations in
IEEE StdC95.1-1991 and OSHARegulation,29, CFR.
Available from DLA Document Services, Building 4/D, 700 Robbins Ave., 9. Preparation of Apparatus
Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
9.1 New and Existing Durable Relocatable Enclosure
Available from Occupational Safety and Health Administration (OSHA), 200
Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov. Testing—Testingofnewdurablerigidwallrelocatableshielded
E1851−21
TABLE 2 Test Apparatus
Disconnect the receiving antenna from the nearest cable and
Equipment Characteristics replace the receiving antenna with a dummy load (resistive
Oscillator(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz, load matched to the characteristic impedance of the receiving
300 MHz to 500 MHz, 900 MHz to 1000 MHz,
system)asshowninFig.3.Measuredlevelsshallbenegligible
8.5 GHz to 10.5 GHz
sotherequireddynamicrangesaremaintained.Ifthemeasured
Power Amplifier(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz,
A
300 MHz to 500 MHz, 900 MHz to 1000
levels are larger than expected, determine the penetration
A
MHz, 8.5 GHz to 10.5 GHz, amplification and
points and correct the identified leakage points. Repeat the
noise figures as required for dynamic range
Preamplifier(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz,
receiving equipment coupling measurements until negligible
300 MHz to 500 MHz, 900 MHz to 1000 MHz,
levels are maintained.
8.5 GHz to 10.5 GHz, amplification and noise
9.3.3 Perform a noise measurement with the following
figures as required for dynamic range
Receiver(s)/Spectrum 140 kHz to 160 kHz, 14 MHz to 16 MHz,
equipment setup. Place the receiving antenna and equipment
Analyzer(s) 300 MHz to 500 MHz, 900 MHz to 1000 MHz,
inside the enclosure and turn off the transmitting antenna
8.5 GHz to 10.5 GHz
B B
placedoutsidetheenclosure(seeFig.4).Thereceivingantenna
Antenna Kit 140 kHz to 160 kHz, 14 MHz to 16 MHz,
C
300 MHz to 500 MHz, 900 MHZ to 1000
can be placed outside the enclosure. When this is done an
C D
MHz, 8.5 GHz to 10.5 GHz
attenuator shall be inserted between the receiving antenna and
Miscellaneous Cables and
receiving equipment, and it shall be set to a shielding effec-
E
Attenuators as Required
tiveness level of the enclosure being tested. Measure the noise
A
The power amplifier output is usually matched to an unbalanced to balanced
level at each frequency to be used for testing.
(balun) transformer; the balanced output is matched to a balanced dipole.
B
9.3.4 After noise levels have been found negligible (or the
Circular loop antenna whose diameter is 30 cm (1 ft) shall be used.The shielded
circular receiving antenna can have multiple turns, but the total length of wire
test equipment has been modified to make the penetration
forming the loop shall be less than ⁄6 wavelength.
negligible), position the transmitting and receiving antennas in
C
Any antenna that radiates at the prescribed frequencies may be used. However,
accordance with the procedures detailed in Section 11. For
antennasthatrequirealargeclearspaceinthedirectionofwavepropagationshall
not be used where clear space is limited for testing. Examples of such antennas
each location, use the receiving antenna as a probe to locate
are linearly polarized log periodic dipole and circularly polarized conical spiral
areas of maximum penetration. Alternatively, a commercial
antennas.Proceduresarewrittenassuminguseofdipoleantennasforplanewave
leak detector may be used. Check all penetrations such as
measurements. If a dipole antenna is used as a receiving antenna, its length shall
be less than ⁄6 of wavelength. The receiving antenna is usually connected to a
doors, power line filters, air vents, seams, and coaxial cable
balun then to an attenuator.
D fittings. If the performance of the enclosure appears to be
Any antenna that radiates at the prescribed frequencies may be used except a
linearly polarized log periodic dipole antenna or circularly polarized conical spiral
inadequate for its design, remedial measures are suggested
antenna. Procedures are written assuming use of aperture antennas for high
prior to complete testing. Identify regions of significantly
frequency plane wave measurements. An isolator is usually used between the
greater field penetration for later measurements.
source and its antenna to minimize variation of power between reference and test
measurements.
E
Well shielded coaxial cable such as flexible semi-rigid coaxial cable, RG-214 or
10. Calibration Procedures
RG-223, shall be used.
10.1 Magnetic Field Calibration Procedure—Conduct the
calibration for magnetic field measurements for each magnetic
fieldtestfrequencyasshowninFig.1a.Choosetestequipment
enclosures can be conducted at the manufacturing site. Manu-
that provides a dynamic range of at least 10 dB (20 dB is
facturing site testing can locate structural defects or weak-
preferable(seeNote1))inexcessoftheshieldingeffectiveness
nessesorbothandcorrectionsmaybeeasilyimplemented.For
requirement at the test frequency. Place the loops of the
existing structures, weaknesses can be determined and cor-
transmitting and receiving antennas in a coplanar configura-
rected during maintenance or periodic retesting.
tion. Place the transmitting and receiving antennas so the
distance between them is 90 cm (3 ft) plus the thickness of the
9.2 Movable Equipment—Moveable equipment containing
metal,notnormallyhousedintheenclosureorattachedoutside enclosure (see Fig. 1a). If an attenuator is used as the basis for
the desired measurement, the attenuator shall be calibrated and
the enclosure, shall be removed from the enclosure prior to
making measurements. the results shall be documented. The attenuator impedance
shall match the system transmission line impedance. Place the
9.3 Preliminary Procedures—Perform the following pre-
receiving system, but not the receiving antenna, inside the
liminary test on all accessible shielding faces to detect weak
enclosure.
points and to permit remedy of shielding defects caused by
10.1.1 During calibration no other equipment or electro-
faulty assembly and poor workmanship prior to actual mea-
magnetic reflectors (except ground) shall be closer than three
surement.
timestheantennaseparation.Theantennasshallbeatleast1m
9.3.1 With the transmitting antenna turned off, perform a
(3.3 ft) above the ground.
continuous wave (cw) measurement at each frequency to be
10.1.2 Record the received signal strength for each fre-
used for testing to ensure that no emitters are nearby that may
quency and transmitting antenna polarization as the calibration
causeinterference.Frequencyadjustmentsmaybenecessaryto
signal (V ) for that configuration. Record all equipment
c
avoid interference. Setup for this measurement is the reference
settings, including generator loop current or transmit power.
measurement (see Section 10 and Fig. 1a and Fig. 2a).
9.3.2 Additionally, perform a receiving equipment coupling 10.2 Plane Wave Calibration Procedure—Conduct the cali-
measurement. The setup for this measurement is the reference bration for plane wave measurements for each plane wave test
measurement (Section 10) with the following exceptions. frequency and antenna polarization as shown in Fig. 2a.
E1851−21
FIG. 1Magnetic Field Test Procedures
Choose test equipment that provides a dynamic range of at 10.2.1 During calibration, no other equipment or electro-
least 10 dB (20 dB is preferable (see Note 1)) in excess of the magnetic reflectors (except ground) shall be closer than three
shielding effectiveness requirement at the test frequency. For
timestheantennaseparation.Theantennasshallbeatleast1m
dipole antennas, place the transmitting and receiving antennas
(3.3 ft) above the ground.
so both antennas lie in the same plane (coplanar) and their
10.2.2 Record the highest received signal strength for each
elements are parallel. For aperture antennas, place the trans-
frequency and both antenna polarizations as the calibration
mitting and receiving antennas so their apertures are parallel.
signal (V ) for that configuration. Record all equipment
c
Separation distance between the antennas shall be as large as
settings, including generator output.
possible within dynamic range constraints, but at least 2.5 m
10.3 Antenna Coverage—Measure the maximum test area
(8.2 ft) plus enclosure thickness. Place the receiving system,
during the calibration. Place the vertically polarized transmit-
but not the receiving antenna, inside the enclosure. Vary the
ting antenna at least 2.5 m (8.2 ft) away from the vertically
receiving antenna position 60.3 m (1 ft) from its nominal
location toward and away from the transmitting antenna to polarized receiving antenna, move the receiving antenna hori-
zontally from left to right from its center, and measure the
measure the local maximum, but do not vary the antenna
alignment or polarization. distance X (m) between the−3 dB points (below the peak
E1851−21
FIG. 2Plane Wave Field Test Procedures
amplitude). Repeat the above procedure by moving the receiv- section test point (see 11.1.4) and other openings (see 11.1.6).
ing antenna up and down from its center position without Cross-polarizationmeasurementsarenotrequired.Recordonly
changingeitherantennapolarizationsandmeasurethedistance the maximum received signal strength as the swept measured
Y (m) between the−3 dB points. signal (V ) for that test point, frequency, and transmitting
m
antenna polarization.
11. Test Measurement Procedures
11.1.1.3 After completion of a series of test measurements,
not to exceed 4 h, repeat the reference level calibration
11.1 Magnetic Field Test Measurement Procedure—
determined in Section 10 to ensure there has been no deviation
Conduct the magnetic field test measurement as shown in Fig.
greater than 1dB or 2 dB for the duration of the measurement
1b. Use the same equipment, antennas, cables, loop current or
period.Ifonlyasmalldeviationisfound(1dBor2dB),donot
transmit power, and equipment settings (except attenuator
adjust the data in determining the shielding effectiveness. If a
settings) that were used in the calibration sequences.
greater deviation is found, investigate the transmitter and
11.1.1 General Test Procedures:
receiver hardware, cables, connectors, and other test equip-
11.1.1.1 Place the transmitting antenna outside the test
ment. When the source of the deviation is located, repair or
structure and center it on the test point. Place the antennas in
replace the faulty hardware and retest the affected test points.
coplanar orientation with the coplanar normal to the surface of
11.1.2 Test Frequencies—Obtain the magnetic field loop
the shield surface. The distance from the transmitting antenna
measurements at 150 kHz and 14 MHz. These test frequencies
to the test point shall be 0.6 m (2 ft) (see Fig. 1).
may be adjusted if the interference conditions described in 6.2
11.1.1.2 Place the receiving antenna inside the test structure
occur. Additional measurements may be performed within 10
maintaining the same polarization. Sweep the receiving an-
kHz to 20 MHz if specified by the procuring agency.
tenna along the seams or edges within the test point area
keeping the receiving antenna 0.3 m (1 ft) from the test point 11.1.3 Corners and Edges:
surface until a maximum signal is received. Both horizontal 11.1.3.1 Test PointAssignment—Forrectangularenclosures,
andverticalcoplanarmeasurementsshallbeperformedateach a corner is formed where three panels meet. Assign three test
E1851−21
FIG. 3Equipment Coupling Measurement
points to each corner. Locate these three corner test points at a 11.1.4 Sections and Seams:
distance of 0.3 m (1 ft) from the interior corner along the three 11.1.4.1 Test Point Assignment—A shielded enclosure is
edges where three panels meet as shown in Fig. 5. usuallycomprisedofoneormoreintegrallyfabricatedsections
(a)An edge is formed where two non-planar panels meet. such as a roof panel or a formed knee-wall panel. These
Determine the length of an edge by measuring the distance sectionsareattachedtogetherdirectlyortoacommonsupport-
along the edge between the corner test points. The edge length ing frame. Seams are formed as a result of connecting sections
determination applies to curvilinear surfaces as well. Assign together.
edge test points that are uniformly spaced along the edge by (a)Sections made of metallic panels do not require testing
dividing the edge length into equal segments not to exceed 0.6 except where seams are formed. Floor sections do not require
m (2 ft) as shown in Fig. 6. Assign an additional test point if testing even if they have seams, unless otherwise specified by
any test point interval exceeds 0.6 m (2 ft). a procuring agency. Assign seam test points that are spaced
11.1.3.2 Antenna Orientation—For fully accessible corners, uniformly along each seam at a spacing not to exceed 0.6 m (2
place the transmitting and receiving antennas in a coplanar ft) as shown in Fig. 6. The seam test point spacing applies to
orientation with the line between the center of antennas angled curvilinear surfaces as well. For seams less than 0.6 m (2 ft)
at 45° to the interior shielding surfaces at each test point (see long, assign a single test point at the seam midpoint.Assign an
Fig. 7e). For partially accessible corners, orient the transmit- additional test point if any interval exceeds 0.6 m (2 ft). Any
ting and receiving antennas as shown in Fig. 7d. Position the test points that overlap with each other can be eliminated.
antennas for edge test points as shown in Fig. 7e. Obtain one 11.1.4.2 Antenna Orientation—Place the transmitting and
test measurement for each corner test point and each edge test receiving antennas in coplanar orientation as indicated in 11.1
point. with the coplane of antennas perpendicular to the seam line at
E1851−21
FIG. 4Noise Measurement Procedures
each seam test point. Obtain one measurement for each seam measurements, first with the transmitting antenna vertically
test point with the coplane of the antennas perpendicular to the polarized and then horizontally polarized.
seam line. (a)Obtain one measurement for each door seam test point
11.1.5 Doors: and obtain two measurements for each door corner test point
11.1.5.1 Test Point Assignment—Assign one test point for (see Fig. 7). Record the highest signal and the corresponding
each door corner. In addition, the vertical seam test points antenna polarization.
consist of two test points at one-third the distance from the top 11.1.6 Other Openings—This section describes test proce-
of the door and one-third the distance from the bottom of the dures for openings such as hatches, power/signal entry panels,
door. The horizontal seam test points are the center of each ventilation/environmental control unit openings, and so forth.
horizontal door seam. See Fig. 7a and Fig. 7b. 11.1.6.1 Test PointAssignment—Assignonetestpointatthe
11.1.5.2 Antenna Orientation—Place the transmitting and geometric center of the opening. For each opening larger than
receiving antennas in coplanar orientation as indicated in 11.1 0.6m(2ft)by0.6m(2ft)assignadditionaltestpointstocover
with the coplane of antennas perpendicular to the door seam at theentireopening.Anytestpointsthatoverlapwith each other
eachtestpoint(seeFig.7a).Doorcornertestpointsrequiretwo can be eliminated.
E1851−21
FIG. 5Corner Test Point Assignment
FIG. 6Edge Seam Test Point Assignment
11.1.6.2 Antenna Orientation—Place the transmitting and
receiving antennas in coplanar orientation as indicated in 11.1.
E1851−21
FIG. 7Door, Seam, and Edge Measurements for Magnetic Field
Obtain two measur
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1851 − 15 E1851 − 21
Standard Test Method for
Electromagnetic Shielding Effectiveness of Durable Rigid
Wall Relocatable Structures
This standard is issued under the fixed designation E1851; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the determination of the electromagnetic shielding effectiveness of durable relocatable shielded
enclosures.
1.1.1 The intended application of this test method is for virgin shielded enclosures that do not have any equipment or equipment
racks. It is recommended that tests be conducted before the interior finish work begins. However, the shield assembly including
all enclosure penetrations shall be completed and required penetration protection devices shall be installed in accordance with the
design specification. The test method can also be used on existing shielded enclosures after repair work is done to verify
workmanship, but it may be necessary to remove equipment or equipment racks to gain access to a test area.
1.1.2 The test procedures delineated in this document are comprehensive and may require several days to complete for a room-size
shielded enclosure. A user can apply this test method for a first article test that requires proof of concept and validation of design
and fabrication technique. Appendix X2 provides guidance on choosing test points so shielding effectiveness tests on a room-size
shielded enclosure may be completed in about one-half day for which it applies to shielded enclosures coming off an assembly line.
1.2 This test method is for use in the following frequency ranges: 140 to 160 kHz, 14 140 kHz to 160 kHz, 14 MHz to 16 MHz,
300300 MHz to 500 MHz, 900900 MHz to 1000 MHz, and 8.58.5 GHz to 10.5 GHz. 10.5 GHz. Specific test frequencies within
these ranges are required (see 11.1.1 and 11.2.1). Additional measurements in the range of 10 kHz to 10.5 GHz may be performed.
For specific applications, the frequency range may be extended from 50 Hz to 40 GHz. Appendix X1 provides guidance on
selecting measurement frequencies.
1.3 This test method is not applicable to individual components such as separate walls, floors, ceilings, or shielded racks.
1.4 This standard may involve hazardous materials, operations, equipment, or any combination.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.after
SI units are provided for information only and are not considered standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
This test method is under the jurisdiction of ASTM Committee E06 on Performance of Buildings and is the direct responsibility of Subcommittee E06.53 on Materials
and Processes for Durable Rigidwall Relocatable Structures.
Current edition approved Sept. 1, 2015Feb. 1, 2021. Published September 2015February 2021. Originally approved in 1997. Last previous edition approved in 20092015
as E1851-09.-15. DOI: 10.1520/E1851-15.10.1520/E1851-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1851 − 21
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E631 Terminology of Building Constructions
E1749 Terminology Relating to Rigid Wall Relocatable Shelters
2.2 IEEE Standards:
IEEE Std 299-1997 IEEE Standard Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures
IEEE Std C95.1-1991 IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic
Fields, 3 kHz to 300 GHz
2.3 Military Standard:
MIL-STD-188-125 High Altitude Electromagnetic Pulse (HEMP) Protection for Ground Based C I Facilities Performing
Critical, Time-Urgent Missions
2.4 OSHA Standard:
OSHA Regulation, 29 CFR 1910, Department of Labor, July 1992
TABLE 1 Test Frequencies and Test Configurations
Corresponding Test
Nominal Test Frequency
Configuration
150 kHz and 14 MHz Fig. 1
400 MHz, 1000 MHz, and 10 GHz Fig. 2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE), 445 Hoes Ln., Piscataway, NJ 08854-4141, http://www.ieee.org.
Available from DLA Document Services, Building 4/D, 700 Robbins Ave., Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
Available from Occupational Safety and Health Administration (OSHA), 200 Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
E1851 − 21
3. Terminology
3.1 Definitions—See Terminologies E631 and E1749 for definitions of general terms used in this test method.
3.1 Definitions:
3.1.1 For definitions of general terms related to building construction used in this test method, refer to Terminology E631, and for
general terms related to rigid wall relocatable shelters, refer to Terminology E1749.
4. Summary of Test Method
4.1 Test Configuration—A transmitting antenna is connected to an electromagnetic source set to a specific frequency and
amplitude. A receiving antenna is placed a specified distance from the transmitting antenna, and the received electromagnetic field
level is recorded as a reference or calibration measurement. The transmitting antenna and electromagnetic source are placed outside
the shielded enclosure. The receiving antenna and associated test equipment are placed inside the shielded enclosure. The
transmitting and receiving antenna’s separation, frequency, and amplitude are the reference measurements. The transmitting and
receiving antennas are at the same height for a given test point. The received electromagnetic field level is recorded as the test
measurement. The ratio of the test measurement to the reference measurement is the electromagnetic shielding effectiveness of the
shielded structure at the measurement location and frequency. The logarithm of this ratio is typically used in expressing the
shielding effectiveness in decibels.
4.2 Test Frequencies—A summary of nominal test frequencies and corresponding test configurations is shown in Table 1.
5. Significance and Use
5.1 This standard provides measurement procedures for determining the electromagnetic shielding effectiveness of durable rigid
wall relocatable shielded enclosures. This standard specifies a method for comparing the shielded enclosure performance of
structures provided by different suppliers. In addition, this standard is written to minimize variations in measured shielding
effectiveness at a given frequency and test point regardless of test personnel, equipment, and test site. Therefore, the shielding
effectiveness of a durable rigid wall relocatable shielded enclosure of any size from any supplier can be determined. This standard
specifies a minimum set of measurements at a given frequency and a minimum set of frequencies to determine shielding
effectiveness.
5.2 Source Fields—Performance of a shielded enclosure is to be assessed for two source fields: magnetic and plane wave.
5.2.1 Magnetic Field Measurements—The attenuation provided by a shielded enclosure is assessed by using a local source to
generate the near field. The magnetic field measurements are specified for two narrow frequency bands: 140140 kHz to 160 kHz
and 1414 MHz to 16 MHz.
5.2.2 Plane Wave Measurements—The attenuation provided by a shielded enclosure is assessed by using a locally generated
distant source or plane wave field. The plane wave measurements are specified for three narrow frequency bands: 300300 MHz
to 500 MHz, 900900 MHz to 1000 MHz, and 8.58.5 GHz to 10.5 GHz.
6. Interferences
6.1 Interference with Electronic Equipment—Care shall be taken to avoid interference with other electronic equipment operating
in the vicinity.
6.2 Operational Impact Analysis and Risk—The electromagnetic barrier must remain intact during the shielding effectiveness
measurement sequence, and use of electrically noisy equipment must be restricted. Therefore, construction activity or unusual
operations (facility modification or maintenance) may be affected. Radiated signal levels should present no hazard to equipment,
but frequency adjustments may be required to avoid self interference or interference with nearby facilities. Record the actual test
frequencies. Normal electrical safety precautions apply.
7. Apparatus
7.1 The required apparatus is identified in Table 2. Choose test equipment that provides a dynamic range of at least 10 dB (20 dB
E1851 − 21
TABLE 2 Test Apparatus
Equipment Characteristics
Oscillator(s) 140 to 160 kHz, 14 to 16 MHz, 300 to 500 MHz,
900 to 1000 MHz, 8.5 to 10.5 GHz
Oscillator(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz,
300 MHz to 500 MHz, 900 MHz to 1000 MHz,
8.5 GHz to 10.5 GHz
Power Amplifier(s) 140 to 160 kHz, 14 to 16 MHz, 300 to 500
A A
MHz, 900 to 1000 MHz, 8.5 to 10.5 GHz,
amplification and noise figures as required for
dynamic range
Power Amplifier(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz,
A
300 MHz to 500 MHz, 900 MHz to 1000
A
MHz, 8.5 GHz to 10.5 GHz, amplification and
noise figures as required for dynamic range
Preamplifier(s) 140 to 160 kHz, 14 to 16 MHz, 300 to 500 MHz,
900 to 1000 MHz, 8.5 to 10.5 GHz,
amplification and noise figures as required for
dynamic range
Preamplifier(s) 140 kHz to 160 kHz, 14 MHz to 16 MHz,
300 MHz to 500 MHz, 900 MHz to 1000 MHz,
8.5 GHz to 10.5 GHz, amplification and noise
figures as required for dynamic range
Receiver(s)/Spectrum 140 to 160 kHz, 14 to 16 MHz, 300 to 500 MHz,
Analyzer(s) 900 to 1000 MHz, 8.5 to 10.5 GHz
Receiver(s)/Spectrum 140 kHz to 160 kHz, 14 MHz to 16 MHz,
Analyzer(s) 300 MHz to 500 MHz, 900 MHz to 1000 MHz,
8.5 GHz to 10.5 GHz
B B
Antenna Kit 140 to 160 kHz, 14 to 16 MHz, 300 to 500
C C D
MHz, 900 to 1000 MHz, 8.5 to 10.5 GHz
B B
Antenna Kit 140 kHz to 160 kHz, 14 MHz to 16 MHz,
C
300 MHz to 500 MHz, 900 MHZ to 1000
C D
MHz, 8.5 GHz to 10.5 GHz
Miscellaneous Cables and
E
Attenuators as Required
A
The power amplifier output is usually matched to an unbalanced to balanced
(balun) transformer; the balanced output is matched to a balanced dipole.
B
Circular loop antenna whose diameter is 30 cm (1 ft) shall be used. The shielded
circular receiving antenna can have multiple turns, but the total length of wire
forming the loop shall be less than ⁄6 wavelength.
C
Any antenna that radiates at the prescribed frequencies may be used. However,
antennas that require a large clear space in the direction of wave propagation shall
not be used where clear space is limited for testing. Examples of such antennas
are linearly polarized log periodic dipole and circularly polarized conical spiral
antennas. Procedures are written assuming use of dipole antennas for plane wave
measurements. If a dipole antenna is used as a receiving antenna, its length shall
be less than ⁄6 of wavelength. The receiving antenna is usually connected to a
balun then to an attenuator.
D
Any antenna that radiates at the prescribed frequencies may be used except a
linearly polarized log periodic dipole antenna or circularly polarized conical spiral
antenna. Procedures are written assuming use of aperture antennas for high
frequency plane wave measurements. An isolator is usually used between the
source and its antenna to minimize variation of power between reference and test
measurements.
E
Well shielded coaxial cable such as flexible semi-rigid coaxial cable, RG-214 or
RG-223, shall be used.
is preferable (see[see Note 1))]) in excess of the shielding effectiveness requirement at the test frequency.
E1851 − 21
FIG. 1 Magnetic Field Test Procedures
NOTE 1—20 dB of dynamic range makes the test easier to perform by less experienced personnel. The standard uses a minimum of 10 dB because it offers
a lower cost solution to testing durable rigid wall relocatable structures. If the existing test equipment has 20 dB of dynamic range then 20 dB of dynamic
range should be used. It makes the hot spots stand out more clearly from the background noise on the LCD displays on spectrum analyzers.
8. Hazards
8.1 For human exposure to electromagnetic energy in controlled environments, the maximum permissible exposure to electric and
magnetic field strengths shall be minimized to the maximum extent possible. Acceptable levels can be found in IEEE
Std C95.1-1991 and OSHA Regulation, 29, CFR.
9. Preparation of Apparatus
9.1 New and Existing Durable Relocatable Enclosure Testing—Testing of new durable rigid wall relocatable shielded enclosures
E1851 − 21
can be conducted at the manufacturing site. Manufacturing site testing can locate structural defects or weaknesses or both and
corrections may be easily implemented. For existing structures, weaknesses can be determined and corrected during maintenance
or periodic retesting.
9.2 Movable Equipment—Moveable equipment containing metal, not normally housed in the enclosure or attached outside the
enclosure, shall be removed from the enclosure prior to making measurements.
9.3 Preliminary Procedures—Perform the following preliminary test on all accessible shielding faces to detect weak points and
to permit remedy of shielding defects caused by faulty assembly and poor workmanship prior to actual measurement.
9.3.1 With the transmitting antenna turned off, perform a continuous wave (cw) measurement at each frequency to be used for
testing to ensure that no emitters are nearby that may cause interference. Frequency adjustments may be necessary to avoid
interference. Setup for this measurement is the reference measurement (see Section 10 and Fig. 1a and Fig. 2a).
9.3.2 Additionally, perform a receiving equipment coupling measurement. The setup for this measurement is the reference
measurement (Section 10) with the following exceptions. Disconnect the receiving antenna from the nearest cable and replace the
receiving antenna with a dummy load (resistive load matched to the characteristic impedance of the receiving system) as shown
in Fig. 3. Measured levels shall be negligible so the required dynamic ranges are maintained. If the measured levels are larger than
expected, determine the penetration points and correct the identified leakage points. Repeat the receiving equipment coupling
measurements until negligible levels are maintained.
9.3.3 Perform a noise measurement with the following equipment setup. Place the receiving antenna and equipment inside the
FIG. 2 Plane Wave Field Test Procedures
E1851 − 21
FIG. 3 Equipment Coupling Measurement
enclosure and turn off the transmitting antenna placed outside the enclosure (see Fig. 4). The receiving antenna can be placed
outside the enclosure. When this is done an attenuator shall be inserted between the receiving antenna and receiving equipment,
and it shall be set to a shielding effectiveness level of the enclosure being tested. Measure the noise level at each frequency to be
used for testing.
9.3.4 After noise levels have been found negligible (or the test equipment has been modified to make the penetration negligible),
position the transmitting and receiving antennas in accordance with the procedures detailed in Section 11. For each location, use
the receiving antenna as a probe to locate areas of maximum penetration. Alternatively, a commercial leak detector may be used.
Check all penetrations such as doors, power line filters, air vents, seams, and coaxial cable fittings. If the performance of the
enclosure appears to be inadequate for its design, remedial measures are suggested prior to complete testing. Identify regions of
significantly greater field penetration for later measurements.
10. Calibration Procedures
10.1 Magnetic Field Calibration Procedure—Conduct the calibration for magnetic field measurements for each magnetic field test
frequency as shown in Fig. 1a. Choose test equipment that provides a dynamic range of at least 10 dB (20 dB is preferable (see
Note 1)) in excess of the shielding effectiveness requirement at the test frequency. Place the loops of the transmitting and receiving
antennas in a coplanar configuration. Place the transmitting and receiving antennas so the distance between them is 90 cm (3 ft)
plus the thickness of the enclosure (see Fig. 1a). If an attenuator is used as the basis for the desired measurement, the attenuator
E1851 − 21
FIG. 4 Noise Measurement Procedures
shall be calibrated and the results shall be documented. The attenuator impedance shall match the system transmission line
impedance. Place the receiving system, but not the receiving antenna, inside the enclosure.
10.1.1 During calibration no other equipment or electromagnetic reflectors (except ground) shall be closer than three times the
antenna separation. The antennas shall be at least 1 m (3.3 ft) above the ground.
10.1.2 Record the received signal strength for each frequency and transmitting antenna polarization as the calibration signal (V )
c
for that configuration. Record all equipment settings, including generator loop current or transmit power.
10.2 Plane Wave Calibration Procedure—Conduct the calibration for plane wave measurements for each plane wave test
frequency and antenna polarization as shown in Fig. 2a. Choose test equipment that provides a dynamic range of at least 10 dB
(20 dB is preferable (see Note 1)) in excess of the shielding effectiveness requirement at the test frequency. For dipole antennas,
place the transmitting and receiving antennas so both antennas lie in the same plane (coplanar) and their elements are parallel. For
aperture antennas, place the transmitting and receiving antennas so their apertures are parallel. Separation distance between the
antennas shall be as large as possible within dynamic range constraints, but at least 2.5 m (8.2 ft) plus enclosure thickness. Place
E1851 − 21
the receiving system, but not the receiving antenna, inside the enclosure. Vary the receiving antenna position 60.3 m (1 ft) from
its nominal location toward and away from the transmitting antenna to measure the local maximum, but do not vary the antenna
alignment or polarization.
10.2.1 During calibration, no other equipment or electromagnetic reflectors (except ground) shall be closer than three times the
antenna separation. The antennas shall be at least 1 m (3.3 ft) above the ground.
10.2.2 Record the highest received signal strength for each frequency and both antenna polarizations as the calibration signal (V )
c
for that configuration. Record all equipment settings, including generator output.
10.3 Antenna Coverage—Measure the maximum test area during the calibration. Place the vertically polarized transmitting
antenna at least 2.5 m (8.2 ft) away from the vertically polarized receiving antenna, move the receiving antenna horizontally from
left to right from its center, and measure the distance X (m) between the −3 dB points (below the peak amplitude). Repeat the above
procedure by moving the receiving antenna up and down from its center position without changing either antenna polarizations
and measure the distance Y (m) between the −3 dB points.
11. Test Measurement Procedures
11.1 Magnetic Field Test Measurement Procedure—Conduct the magnetic field test measurement as shown in Fig. 1b. Use the
same equipment, antennas, cables, loop current or transmit power, and equipment settings (except attenuator settings) that were
used in the calibration sequences.
11.1.1 General Test Procedures:
11.1.1.1 Place the transmitting antenna outside the test structure and center it on the test point. Place the antennas in coplanar
orientation with the coplanar normal to the surface of the shield surface. The distance from the transmitting antenna to the test point
shall be 0.6 m (2 ft) (see Fig. 1).
11.1.1.2 Place the receiving antenna inside the test structure maintaining the same polarization. Sweep the receiving antenna along
the seams or edges within the test point area keeping the receiving antenna 0.3 m (1 ft) from the test point surface until a maximum
signal is received. Both horizontal and vertical coplanar measurements shall be performed at each section test point (see 11.1.4)
and other openings (see 11.1.6). Cross-polarization measurements are not required. Record only the maximum received signal
strength as the swept measured signal (V ) for that test point, frequency, and transmitting antenna polarization.
m
11.1.1.3 After completion of a series of test measurements, not to exceed 4 h, repeat the reference level calibration determined
in Section 10 to ensure there has been no deviation greater than 11 dB or 2 dB for the duration of the measurement period. If only
a small deviation is found (1(1 dB or 2 dB), do not adjust the data in determining the shielding effectiveness. If a greater deviation
is found, investigate the transmitter and receiver hardware, cables, connectors, and other test equipment. When the source of the
deviation is located, repair or replace the faulty hardware and retest the affected test points.
11.1.2 Test Frequencies—Obtain the magnetic field loop measurements at 150 kHz and 14 MHz. These test frequencies may be
adjusted if the interference conditions described in 6.2 occur. Additional measurements may be performed within 10 kHz to 20
MHz if specified by the procuring agency.
11.1.3 Corners and Edges:
11.1.3.1 Test Point Assignment—For rectangular enclosures, a corner is formed where three panels meet. Assign three test points
to each corner. Locate these three corner test points at a distance of 0.3 m (1 ft) from the interior corner along the three edges where
three panels meet as shown in Fig. 5.
(a) An edge is formed where two non-planar panels meet. Determine the length of an edge by measuring the distance along
the edge between the corner test points. The edge length determination applies to curvilinear surfaces as well. Assign edge test
points that are uniformly spaced along the edge by dividing the edge length into equal segments not to exceed 0.6 m (2 ft) as shown
in Fig. 6. Assign an additional test point if any test point interval exceeds 0.6 m (2 ft).
11.1.3.2 Antenna Orientation—For fully accessible corners, place the transmitting and receiving antennas in a coplanar orientation
with the line between the center of antennas angled at 45° to the interior shielding surfaces at each test point (see Fig. 7e). For
partially accessible corners, orient the transmitting and receiving antennas as shown in Fig. 7d. Position the antennas for edge test
points as shown in Fig. 7e. Obtain one test measurement for each corner test point and each edge test point.
E1851 − 21
FIG. 5 Corner Test Point Assignment
FIG. 6 Edge Seam Test Point Assignment
11.1.4 Sections and Seams:
E1851 − 21
FIG. 7 Door, Seam, and Edge Measurements for Magnetic Field
11.1.4.1 Test Point Assignment—A shielded enclosure is usually comprised of one or more integrally fabricated sections such as
a roof panel or a formed knee-wall panel. These sections are attached together directly or to a common supporting frame. Seams
are formed as a result of connecting sections together.
(a) Sections made of metallic panels do not require testing except where seams are formed. Floor sections do not require testing
even if they have seams, unless otherwise specified by a procuring agency. Assign seam test points that are spaced uniformly along
each seam at a spacing not to exceed 0.6 m (2 ft) as shown in Fig. 6. The seam test point spacing applies to curvilinear surfaces
as well. For seams less than 0.6 m (2 ft) long, assign a single test point at the seam midpoint. Assign an additional test point if
any interval exceeds 0.6 m (2 ft). Any test points that overlap with each other can be eliminated.
11.1.4.2 Antenna Orientation—Place the transmitting and receiving antennas in coplanar orientation as indicated in 11.1 with the
coplane of antennas perpendicular to the seam line at each seam test point. Obtain one measurement for each seam test point with
the coplane of the antennas perpendicular to the seam line.
11.1.5 Doors:
11.1.5.1 Test Point Assignment—Assign one test point for each door corner. In addition, the vertical seam test points consist of
two test points at one-third the distance from the top of the door and one-third the distance from the bottom of the door. The
horizontal seam test points are the center of each horizontal door seam. See Fig. 7a and Fig. 7b.
E1851 − 21
11.1.5.2 Antenna Orientation—Place the transmitting and receiving antennas in coplanar orientation as indicated in 11.1 with the
coplane of antennas perpendicular to the door seam at each test point (see Fig. 7a). Door corner test points require two
measurements, first with the transmitting antenna vertically polarized and then horizontally polarized.
(a) Obtain one measurement for each door seam test point and obtain two measurements for each door corner test point (see
Fig. 7). Record the highest signal and the corresponding antenna polarization.
11.1.6 Other Openings—This section describes tes
...