This part establishes a common validation procedure, equipment under test EUT set-up requirements, and measurement methods for fully anechoic rooms FARs when both radiated electromagneti
Measurand for radiated immunity testing
Electromagnetic radiation significantly impacts most electronic devices, originating from common sources like handheld radio transceivers used by personnel, fixed radio and television transmitters, vehicle radio transmitters, and various industrial electromagnetic sources.
In the frequency range addressed by this standard, far-field conditions may not always be achievable, particularly at lower frequencies Consequently, the disturbance quantity that simulates the actual electromagnetic phenomenon is represented by the "electrical field strength" as defined in this standard.
The electric field strength, measured in decibels (C dB), is the key parameter for determining the disturbance quantity in immunity tests This measurand is calculated separately for both horizontal and vertical polarizations.
Measurand for radiated emission measurements
In a FAR for radiated emission measurements, the measurand is the field strength emitted by the EUT, measured at a distance \(d\) using a linearly-polarized antenna This involves applying the average system transducer factor, \(C_{dB}\), to the maximum voltage recorded at the receiving termination point The measurand is determined separately for both horizontal and vertical polarizations of the receiving antenna and is reported at the reference distance \(d_{reference}\) as outlined in product standards.
General
This clause provides the performance requirements and harmonized FAR validation procedure for both radiated emission measurements and radiated immunity tests.
Validation set-ups
Figures 1 to 4 illustrate various block diagram configurations that can be utilized for the validation procedure Each setup variant includes a transducer reference point (p TR ), which is essential for determining the average system transducer factor as outlined in section 5.4 during the validation process.
The primary instrumentation required for each of these set-ups is summarized in the following bulleted list, and described further in the subsequent lettered list
• Type 1 (Figure 1): signal generator, spectrum analyzer or power meter, field probe
• Type 2 (Figure 2): signal generator, spectrum analyzer or power meter, reference antenna
• Type 3 (Figure 3): network analyzer, reference antenna
• Type 4 (Figure 4): network analyzer, power amplifier, reference antenna p TR FAR
Spectrum analyzer or RF pow er meter
A C1 Attenuation of the cable between the directional coupler and the spectrum analyzer or power meter (dB)
F FP Calibration factor of the field probe (in linear scale)
A DC Attenuation of the directional coupler between power input and power output (dB)
F DC Coupling loss of the directional coupler between power input and forward power output (dB) p TR Transducer reference point
Figure 1 – Type 1 validation block diagramme p TR FAR
Spectrum analyzer or RF pow er meter
A C1 Attenuation of the cable between the directional coupler and the spectrum analyzer or power meter (dB)
A C2 Attenuation of the cable between the reference antenna and the spectrum analyzer (dB)
F RA Antenna factor of the reference antenna [dB(1/m)]
A DC Attenuation of the directional coupler between power input and power output (dB)
F DC Coupling loss of the directional coupler between power input and forward power output (dB) p TR Transducer reference point
Figure 2 – Type 2 validation block diagramme
Port 1 Port 2 p TR FAR p RA
F RA Antenna factor of the reference antenna [dB(1/m)]
A C2 Attenuation of the cable between the reference antenna and the spectrum analyzer (dB) p RA Reference point of the reference antenna p TR Transducer reference point
The attenuation of the cable connecting the reference antenna to the network analyzer can be assessed by normalizing the network analyzer, with p TR and p RA connected for this purpose.
Figure 3 – Type 3 validation block diagramme
Vector network analyzer or scalar network analyzer
A C1 Attenuation of the cable between the directional coupler and the spectrum analyzer or power meter (dB)
A C2 Attenuation of the cable between the reference antenna and the spectrum analyzer (dB)
F RA Antenna factor of the reference antenna [dB(1/m)]
A DC Attenuation of the directional coupler between power input and power output (dB)
F DC Coupling loss of the directional coupler between power input and forward power output (dB) p TR Transducer reference point p RA Reference point of the reference antenna
R,A,B Network analyzer ports – output port R, input ports A and B
Figure 4 – Type 4 validation block diagramme
A Fully Anechoic Room (FAR) validation setup includes several essential components Table 1 provides a summary of the required components for various setup types.
The test volume and the validation distance shall be previously specified according to Figure 5 (see 5.5) and definitions 3.12, 3.14 b) Broadband antenna
The position of the broadband antenna is fixed in the room
The antenna factor included with the antenna is unnecessary, as it is established through the transducer factor of the FAR test system during validation and calibration Essential equipment for this process includes an RF power meter, frequency selective voltmeter, or spectrum analyzer, along with a directional coupler, isotropic field probe and monitor, and a reference antenna.
The reference antenna must meet the specifications outlined in section 5.4.2.3 of CISPR 16-1-4 for frequencies between 30 MHz and 1 GHz, as well as section 8.3.3.1 of the same standard for frequencies ranging from 1 GHz to 18 GHz Additionally, a cable is required to connect to the broadband antenna.
Routing to the broadband antenna shall be fixed in the installation
NOTE 2 The loss of the cable to the broadband antenna is determined as part of the FAR system transducer factor during this validation/calibration
To minimize cable influence, it is recommended to install the broadband antenna cable horizontally from the antenna to the absorbers on the back wall, and then vertically from the absorbers to the floor.
The characteristics of RF cables must be established during prior calibration Any discrepancies between the cables used in this calibration and those employed in subsequent testing can be individually assessed This includes the signal source.
RF generator, able to produce a stable signal j) Power amplifier
During the validation and calibration process, as well as during immunity tests, it is essential to monitor the output power For detailed information on harmonics and compression characteristics, please refer to Annex A Additionally, a scalar or vector network analyzer should be utilized.
Instrument for the measurement of the transfer function between two points (S 21 ) or the ratio of two signals (without bridge)
Table 1 – Components required for the different validation set-up types
The equipment utilized across various types includes a Fully Anechoic Room (FAR), Broadband Antenna, RF Power Meter, and Directional Coupler, which are essential for Types 1, 2, 3, and 4 Additionally, an Isotropic Field Probe and Monitor is used in Type 1, while a Reference Antenna is applicable for Types 2, 3, and 4 Cables to the Broadband Antenna and other RF cables are necessary for all types A Signal Source and Power Amplifier are utilized in Types 1 and 2, while a Scalar or Network Analyzer is relevant for Types 3 and 4.
1) Letters preceding a component correspond with items detailed in 5.2
2) “x” indicates component is required; “–“ indicates component is not required.
Test facility description
General
For the purposes of FAR validation, the parameters of 5.3.2 through 5.3.8 shall be specified and clearly documented using text descriptions and photographs in the validation report.
Test volume
The test volume, defined as a cylinder, must fully enclose the maximum dimensions of the Equipment Under Test (EUT) along with its associated cables, as outlined in Clause 6 Key parameters for this test volume include the diameter, the position of the center of the bottom surface, and the height.
Broadband antenna
The broadband antenna must be positioned outside the test volume within a specified FAR, typically at the height of the test volume's center It serves dual purposes: as the receiving antenna for emission measurements and as the transmitting antenna for validation, calibration, and subsequent immunity tests Each set of antennas, covering various frequency ranges, requires a validation and calibration process for accurate immunity testing and emission measurements.
Antenna cables
Antenna cable reflections can impact FAR testing results, making their design and placement crucial During FAR validation, the lengths of antenna cables connected to the broadband antenna must be arranged identically to their configuration in product tests Additionally, any ferrites on the antenna cable should be included in both validation and subsequent EUT testing.
Set-up table
For optimal testing conditions, it is advisable to use set-up tables constructed from nonconductive and low permittivity materials A removable set-up table designed for installation within the test volume is not required to be present during the facility validation process outlined in section 5.6 However, any set-up table situated outside the test volume that is consistently utilized for Equipment Under Test (EUT) assessments must be regarded as part of the FAR facility and should be installed during the validation procedure specified in section 5.6.
Turntable
The minimum recommended facility includes a remotely controlled turntable within the test volume Validation and calibration of the facility must be conducted with the turntable, power feed, and communication cabling positioned in their standard locations, as utilized during Equipment Under Test (EUT) evaluations.
Automated antenna polarization changer
A computer-controlled, automated antenna polarization changer is recommended, to reduce test time.
Absorber configuration
The absorber configuration used for the validation test must be the same as will be used for subsequent EUT testing.
Definition of quantities to be determined by the FAR validation procedure
The quantities to be determined for each sampling position in the FAR validation procedure are outlined in this subclause The system transducer factor, denoted as \$C_{dB,x}\$ in dB(1/m), is specified for a single position represented by \$x\$.
The formula for calculating the decibel level is given by \$dB = 20 \log\left(\frac{f}{15}\right) + 10 \log(1)\$, where \$f\$ represents the frequency in MHz Additionally, \$d\$ denotes the distance in meters between the reference point of the broadband antenna and the reference point of the field probe or reference antenna For further details, refer to section 5.5.
P fn,x is the normalized forward power in W, given by:
P f,x is the forward power at the transducer reference point p TR in W;
E x is the corresponding electric field strength at location x in V/m
NOTE Annex C gives background and rationale about the relationships shown in Equations (1) and (2)
From the individual system transducer factors, C dB,x , the average system transducer factor, C dB, (as defined in 3.3) can be derived using Equation (3):
1 , dB dB (3) where n is the number of sampling points, as determined according to the procedure of 5.5
The standard deviation of the collected samples is calculated using Equation (4), and for each antenna polarization separately This quantity is used for comparison to the validation criteria of 5.7
The standard deviation of the average system transducer factor, denoted as \$s_{dB,C}\$, is computed using Equation (5) for each antenna polarization This measurement is crucial for assessing uncertainty in future Equipment Under Test (EUT) evaluations, as referenced in items 8 of D.1.3 and 9 of D.2.4.
Required sampling positions for FAR validation
The procedure outlined in this section involves measuring the characteristics of a FAR at various positions within a test volume The results will be presented as an average system transducer factor along with the standard deviation, categorized separately for each antenna polarization, namely horizontal and vertical.
FAR measurements and validation will be conducted for both horizontal and vertical antenna polarizations at specified positions, including three heights within the test volume: bottom, middle, and top.
The bottom height \( h_B \) is positioned at 25% of the test volume's height from the bottom It must be at least 20 cm for test volumes under 80 cm in height, and it should be set to 50 cm for test volumes exceeding 2 m.
The top height \( h_T \) is positioned at 25% of the test volume's height from the top It must be at least 20 cm for test volumes under 80 cm and set at 50 cm for volumes exceeding 2 m.
The middle height is situated at 50% of the test volume's height Measurements are taken at five positions across three horizontal planes: center, left, right, front, and rear.
The broadband antenna must be positioned at the center height of the test volume and remain fixed, as illustrated in Figure 5 It is essential that the antenna is not tilted, ensuring that its boresight axis aligns with the primary measurement axis during all measurements Additionally, the field probe or reference antenna within the test volume should be oriented to face the broadband antenna The height and position of the broadband antenna must match the setup that will be used for subsequent equipment testing.
During the validation procedure, the distance from the broadband antenna's reference point to the front of the test volume is denoted as \$d_{validation}\$ It is essential that all antenna masts and supporting structures remain in place throughout this process Only the field probe or reference antenna is moved within the test volume, while the broadband antenna remains stationary Consequently, the actual separation distance between the broadband antenna and each sampling position, \$d_x\$, will differ based on the specific sampling location It is crucial to record the actual separation distance for each position, which will then be utilized for \$d_x\$ in Equation (1).
The sampling positions shall be located such that the phase centre of the reference antenna or field probe shall always be a minimum of 20 cm inside the test volume h B h T d validation
NOTE Parameters are described in 5.5 The cylinder formed by the solid lines represents the test volume
Figure 5 – Locations of the sampling points for FAR validation
FAR validation procedure
General
To begin the measurement process, configure the equipment according to the setups shown in Figures 1 through 4 Next, position the probe or reference antenna at one of the locations depicted in Figure 5, ensuring that the polarization of the broadband antenna is set to horizontal.
The detailed steps for each of the four setup types are outlined in sections 5.6.2 to 5.6.5, while section 5.6.6 addresses the calculations for the average system transducer factor and its standard deviation.
Type 1 validation set-up
To effectively utilize a Type 1 validation setup, follow these steps: first, configure the field probe to single-axis mode to accurately measure the desired polarization Next, adjust the signal generator to the initial frequency of interest Finally, set the output power of the signal generator or amplifier to a constant continuous wave (CW) level that ensures an adequate validation field strength, \$E_x\$ It is important to note that the measurement outcomes remain unaffected by the absolute field strength or power level.
NOTE 1 The signal generator and/or amplifier shall be operated at a power level below its maximum output level, to limit the possible influence of harmonics on the measurement results d) Record the following parameters:
• power indicated at the power meter measurement point, P f,ind,x ,in dBm;
• indicated field strength from the isotropic field probe, E ind,x ,in V/m;
To measure the distance, \( d_x \), between the broadband antenna and the field probe, step the frequency in increments not exceeding 1% Repeat the measurement process until the final frequency is reached Finally, compute the system transducer factor for position \( x \) at each frequency.
C dB , = 20 log MHz −15 −20log + f, ind, −30+ C1 + DC − DC −20log FP × ind , (6)
NOTE 2 The parameters are defined in Figure 1 g) Repeat steps a) through f) for each sampling position h) Repeat steps a) through g) for vertical polarization.
Type 2 validation set-up
The following steps shall be applied when using a Type 2 validation set-up a) Set the signal generator to the first frequency of interest
Set the output power of the signal generator or amplifier to a constant continuous wave (CW) level that ensures an appropriate validation field strength, denoted as E x The measurement outcomes remain unaffected by the absolute field strength or power level.
NOTE 1 The signal generator and/or amplifier shall be operated at a power level below its maximum output level, to limit the possible influence of harmonics on the measurement results b) Record the following parameters:
• power shown by the power meter, P f,ind,x ,in dBm;
• indicated voltage from the spectrum analyzer, V ind,x ,in dB(μV);
To determine the system transducer factor at position \( x \) for each frequency, measure the distance \( d_x \) between the broadband antenna and the reference antenna Next, increment the frequency in steps not exceeding 1%, and repeat the measurement process until the final frequency is reached.
C dB , log MHz −15 −20log + f, ind , −30+ C1 + DC − DC − ind , (7) where
NOTE 2 The parameters are defined in Figure 2 e) Repeat steps a) through d) for each sampling position f) Repeat steps a) through e) for vertical polarization.
Type 3 validation set-up
When utilizing a Type 3 validation setup, it is essential to first normalize the network analyzer before measurements Next, configure the start and stop frequencies of the network analyzer, ensuring proper frequency stepping is established.
• For 30 MHz to 80 MHz: f step ≤ 1 MHz
• For 80 MHz to 500 MHz: f step ≤ 2 MHz
• For 500 MHz to 1 GHz: f step ≤ 5 MHz
• For 1 GHz to 18 GHz: f step ≤ 50 MHz c) Measure and record S 21,x , in dB d) Compute the system transducer factor for position x and for each frequency:
NOTE The parameters are defined in Figure 3 e) Repeat steps a) through d) for each sampling position f) Repeat steps a) through e) for vertical polarization.
Calculation of dB
• For 1 GHz to 18 GHz: f step ≤ 50 MHz c) Measure and record S 21,x , in dB d) Compute the system transducer factor for position x and for each frequency:
NOTE The parameters are defined in Figure 3 e) Repeat steps a) through d) for each sampling position f) Repeat steps a) through e) for vertical polarization
To effectively utilize a Type 4 validation set-up, it is essential to first normalize the network analyzer before measurements Next, configure the start and stop frequency settings on the analyzer, ensuring proper frequency stepping is established.
• For 30 MHz to 80 MHz: f step ≤ 1 MHz
• For 80 MHz to 500 MHz: f step ≤ 2 MHz
• For 500 MHz to 1 GHz: f step ≤ 5 MHz
For frequencies ranging from 1 GHz to 18 GHz, the frequency step should not exceed 50 MHz It is essential to choose an output power for the network analyzer that ensures an adequate validation field strength, denoted as E x The measurement outcomes remain unaffected by the absolute field strength or power level Additionally, it is important to measure and document the signal ratio B/A (R BA,x, in dB) Finally, compute the system transducer factor for position x at each frequency.
( MHz ) ( ) BA , C1 DC DC C2 RA
NOTE The parameters are defined in Figure 4 f) Repeat steps a) through e) for each location g) Repeat steps a) through f) for vertical polarization
5.6.6 Calculation of C dB and s dB , C for all set-up types
For each polarization and frequency, calculate the average system transducer factor using Equation (3), and the standard deviation of the collected samples using Equation (4).
Validation requirement
The FAR validation requirement depends on the standard deviation of the sampled system transducer factors Each polarization's standard deviation, denoted as \$s_{dB,C}\$, must meet the criteria specified in Table 2.
30 MHz to 1 GHz s dB, ≤ C 1,8 dB for all 15 sampling points
1 GHz to 18 GHz s dB, C ≤ 1,8 dB for all 15 sampling points
To meet the criteria, the following conditions must be satisfied: the standard deviation (s dB) must be less than or equal to 3 dB for all 15 sampling points, and the standard deviation must also be less than or equal to 1.8 dB for the 10 points located in the top and middle planes of the test volume.
Validation is valid as long as the test setup for subsequent Equipment Under Test (EUT) remains consistent Consequently, it is essential to thoroughly document the validation setup, including the antenna, absorber configuration, cables, and other components.
Tests must be conducted with the Equipment Under Test (EUT) configured to reflect typical end-use conditions Unless specified otherwise, manufacturer-recommended cables and wiring should be used, and the equipment must remain within its housing with all covers and access panels secured Any deviations from standard operating conditions must be detailed in the test report, and adherence to the manufacturer's setup guidelines should be prioritized whenever feasible Documentation of the setup is essential and should be included in the test report.
The height of the set-up table for both table-top and floor-standing equipment is flexible, as long as the equipment under test fits within the designated test volume and the cable layout meets specific criteria All interface cables, loads, and devices must connect to at least one of each type of interface port on the Equipment Under Test (EUT), with each cable ideally terminating in a device representative of its actual use For multiple interface ports of the same type, a typical number should be connected, although connecting just one load is sufficient if preliminary testing demonstrates that adding more ports does not significantly increase disturbance (beyond 2 dB) or degrade immunity levels The rationale for the port configuration and loading must be documented in the test report.
The number of additional cables should be limited to the condition where the addition of another cable does not decrease the margin by 2 dB with respect to the limit
In certain instances, the ideal configuration of features, loads, interface types, and cables for emissions and immunity testing may differ, necessitating a reconfiguration of the Equipment Under Test (EUT) while still adhering to a standardized EUT arrangement.
The cable layout and termination shall be according to the following requirements:
When following manufacturer installation instructions, cables must be arranged as specified If no specific routing is provided, cables should be positioned to ensure that both vertically and horizontally polarized radiation are adequately accommodated.
A minimum cable length of 1.0 m must be used within the test volume, unless the manufacturer's specifications indicate shorter cables Any excess cable should be neatly bundled at the midpoint to create a 30 cm bundle.
For a typical cable layout in electromagnetic testing, if the manufacturer does not provide specific guidelines, the following arrangements should be followed: i) For table-top equipment under test (EUT), cables connecting to the outside must extend at least 1 meter outside the test volume ii) For floor-standing EUT, cables should run horizontally for at least 0.3 meters within the test volume and vertically according to standard usage, based on the height of the I/O port Additionally, cables that are not connected to any device may be terminated appropriately.
1) Coaxial shielded cables shall be terminated with a coaxial termination (usually 50 Ω or 75 Ω)
Shielded cables featuring multiple inner conductors must adhere to the EUT manufacturer's specifications for both common and differential mode terminations It is essential to connect the common mode termination correctly between the inner conductors or their differential mode termination and the cable shield.
3) Unshielded cables shall have differential mode termination according to the manufacturer's specifications c) The following additional items shall be considered for the EUT set-up:
When testing an EUT that requires associated equipment (AE) for proper operation, it is crucial to ensure that the AE does not interfere with radiated emission measurements or radiated immunity tests The AE can be positioned outside the Faraday Absorber Room (FAR) during testing, provided that suitable connecting interfaces are available on the room's shielding Additionally, implementing measures to prevent RF-signal leakage through interconnection cables may be necessary.
NOTE 2 A device that simulates a telecommunications network is an example of AE AE may be physically located outside the test environment
2) Other methods or equipment used to suppress unwanted emissions from AE shall be located outside the test room
The test report must provide a detailed description of the test setup, including the cable layout, specifications of the attached cables and terminations, as well as the measures implemented to minimize emissions from ancillary equipment outside the test volume.
The EUT perimeter is defined by the components of the EUT situated within the test volume, where validation requirements are met This perimeter encompasses the connecting cables between EUT components, while excluding any cables that extend beyond the test volume Cables exiting the test volume must adhere to the specified layout requirements outlined in this subclause.
Figure 6 – Example test set-up for table-top equipment
EUT perimeter (including connecting cables) Test volume
Figure 7 – Example test set-up for table-top equipment, top view
Figure 8 – Example test set-up for floor-standing equipment
EUT perimeter (including connecting cables)
Figure 9 – Example test set-up for floor-standing equipment, top view
This annex describes the procedures for performing radiated immunity tests in a FAR
The equipment utilized for immunity tests is illustrated in Figures 1 and 2 (refer to section 5.2) Notably, a field probe or reference antenna is unnecessary for these tests, and additional specific parameters are detailed in the subsequent list.
An RF signal generator must effectively cover the desired frequency band and be capable of amplitude modulation using a 1 kHz sine wave with an 80% modulation depth, or according to the specifications outlined in the relevant product standard.