1 Overview of Radiated Immunity Testing in a Reverberation Chamber Presented by Craig Fanning Elite Electronic Engineering Inc Automotive EMC Standards Workshop January 30 & 31, 2006 Dearborn, Michigan USA

2 Overview  Scope  Several SAE Standards cover Reverberation Chamber Radiated Immunity testing on Vehicles and Components  J551-16: Vehicle Level Reverberation Radiated Immunity (Mode Tuned and Mode Stirred Methods Covered)  J : Component Level Reverberation Radiated Immunity (Mode Stir Method Covered)  J : Component Level Reverberation Radiated Immunity (Mode Tuned Method Covered)  These are alternative methods to testing in an Absorber Lined Shielded Enclosure (ALSE) as described in J and J  In all of the above standards, the electromagnetic disturbance is limited to continuous narrow band electromagnetic fields.

3 Overview  Corresponding International Standards:  J551-16: Currently there is no ISO standard for reverberation chamber radiated immunity at the vehicle level. Portions of IEC and IEC were used for development of this standard.  SAE J : Currently there is no ISO standard for Mode Stir reverberation chamber radiated immunity on automotive components. Mode Stir radiated immunity testing is discussed in IEC , however, the main focus of IEC is Mode Tuned techniques.  SAE J : Currently there is currently no ISO standard for Mode Tuned reverberation chamber radiated immunity on automotive components. Mode Tuned radiated immunity testing is covered in IEC and is the basis of the J document.

4 Overview  Terms and Definitions:  Reverberation Chamber: A high Q shielded room whose boundary conditions are changed via a rotating tuner. This results in a time-averaged uniform electric field.  Chamber Quality Factor (Q): Q factor is the measure of a chambers ability to reverberate. The Q factor is effected by the chamber dimensions and wall material.  Tuner: A rotating metallic reflector that changes the boundary conditions in a reverberation chamber as it rotates. As the tuner rotates the nulls and maximums of the field change location. This ensures that the DUT and wiring harness are exposed to a time-averaged uniform field.

5 Typical Reverberation Chamber

6 Chamber Design  When selecting a mode tuned chamber, the desired usable frequency range and internal working volume needs to be considered. This will dictate the chamber size.  For optimum chamber performance, especially at low frequencies, the volume of the chamber should be as large as possible and the room dimensions should not be integer multiples of one another. Rooms with integer multiple dimensions will have degenerative modes (room may not reverberate at all frequencies).  Minimum recommended room dimensions are 4.88m x 3.66m x3.05m (16ft L x 12ft W x 10ft H)  The chamber size and tuner size will effect the lowest usable frequency (frequency cutoff) of the chamber.

7 Tuner Designs  The criteria for tuner design is to ensure its effectiveness in redistributing the energy inside the chamber.  The tuner should be electrically large (greater than or equal to the wavelength at the lowest frequency of operation).  It shall be shaped and oriented to achieve a receive power maximum/minimum ratio of greater than or equal to 20dB. As the tuner rotates, the difference of the Emax and Emin RF fields, measured at a fixed location, shall change by 20dB or greater.  The is tuner is operated in step/stop/step/stop type of operation during Mode Tuned testing.  The tuner is continuously rotated during Mode Stir testing.

8 Tuner Designs: Foam Board Tuner

9 Tuner Designs: Z-Fold Design

10 Tuner Designs: MIL-STD-1344A

11 Mode Tuned vs Mode Stir Testing  Mode Tuned Reverberation:  The tuner needs to be driven via a computer controlled stepper motor in order to achieve a step/stop/step/stop type of operation. Computer will also control RF Generation and RF Monitoring equipment.  The field generating antenna is pointed into the corner of the chamber to eliminate direct coupling to the DUT.  A constant field can be applied to the DUT for a specified dwell time at each tuner stop point.  The number of tuner steps is dependent upon the chamber calibration data (minimum 12 steps is suggested)  Multiple runs with different antenna polarities and DUT orientations are not required. This is due to the loss of field polarity and the DUT is immersed in the applied field.  This method requires chamber characterization per IEC and SAE J , with and without the DUT.

12 Mode Tuned vs Mode Stirred Testing  Mode Stir Reverberation:  The tuner can be rotated continuously with a gear reduction AC motor.  The RPM of the tuner should be adjustable for units with different response times (typically 10-20seconds/revolution).  The field generating antenna is typically pointed into the corner of the chamber to eliminate direct coupling to the DUT. This method requires chamber characterization per SAE J , with and without the DUT.  The dwell at each frequency and modulation tested is typically the time it takes for one full rotation of the tuner.  Multiple runs with different antenna polarities and DUT orientations are not required since the since there is loss of field polarity and the DUT is immersed in the applied field.

13 SAE J551 Part 16 Electromagnetic Immunity – Off-Vehicle Source (Reverberation Chamber Method)-Part 16- Immunity to Radiated Electromagnetic Fields Presented by Craig Fanning Elite Electronic Engineering Inc Automotive EMC Standards Workshop January 30 & 31, 2006 Dearborn, Michigan USA

14 Overview  SAE J specifies Radiated Immunity (Reverberation Chamber) test methods and procedures for the testing of passenger cars and commercial vehicles. J provides a means of coupling RF energy to the electrical system of vehicles. It is an alternative to testing in an Absorber Lined Shielded Enclosure (ALSE) radiated immunity test as described in J  Three methods of reverberation radiated immunity testing are covered in the standard:  Mode Tuned  Mode Stir (Standard)  Mode Stir (Hybrid)

15 Revision of Standard  SAE J is a new standard developed by the SAE Standards Committee. The original publication date was September  The specification is a culmination of test methods currently being used by Vehicle OEMS and Independent Test Laboratories to evaluate vehicle performance when exposed to Radiated RF Fields.  The specification is currently a Surface Vehicle Recommended Practice. After a few years of use and during it’s next revision…the specification will most likely become a Surface Vehicle Standard.

16 International Standards  Corresponding International Standards: Currently there is no ISO standard for reverberation chamber radiated immunity testing at the vehicle level.  The Mode Tuned test methods are a variation of the component test specification SAE J  The Mode Stir (Standard) test methods are a variation of the component test specification SAE J  The Mode Stir (Hybrid) test methods are unique and field uniformity measurements similar to IEC are used for chamber performance verification.  If International Compliance is of concern…a test in an ALSE chamber would currently be required to meet 95/54/EC or 2004/104/EC.

17 Test Configurations - Typical

18 Test Configurations - Typical  The Mode Tuned and Mode Stir (Standard) test methods (Figure 1) are well suited for the evaluation of smaller vehicles such as Motorcycles, Passenger Cars and Pickup Trucks. Chambers needed for the testing of large vehicles may be too lossy for these methods.  Illumination of the entire vehicle is possible without the need of multiple antenna polarizations and antenna positions about the vehicle.  Since the RF field is bombarding the vehicle from many different directions, better coverage of the vehicle is achieved. This reduces the chance of missing a potential issue that may not be found in the ALSE chamber.  Large vehicles may cause chamber loading issues which may not allow the use of these indirect “shoot-in- the-corner” illumination methods.  The Mode Tuned method requires extensive chamber characterization per SAE J and IEC  The Mode Stir (standard) test method requires chamber characterization per SAE J

19 Test Configurations - Hybrid

20 Test Configurations - Hybrid  The Mode Stir (Hybrid) test method (Figure 2) was developed for the testing of large vehicles such as Class 8 Trucks, Truck & Trailer combinations, Busses, Earth Moving Equipment and Agricultural Equipment.  Illumination of large areas of the vehicle is possible depending upon the field uniformity data. Multiple antenna polarizations and antenna positions about the vehicle will usually still be required.  Since the RF field is bombarding the vehicle from many different directions, better coverage of the vehicle is achieved. This reduces the chance of missing a potential issue that may not be found in an ALSE chamber.  The dwell time at each frequency is the time it takes for the slowest tuner to make one full rotation (typically seconds).

21 Additional Information  During Mode Stir (Alternate) and Mode Stir (Hybrid) tests, the field intensity generated is typically measured with a receive antenna in conjunction with a spectrum analyzer. The fast sweep speed of a spectrum analyzer will allow the maximum field to be measured. The use of an isotropic probe is allowed only if the isotropic probe has a high sampling rate (50Hz suggested). A high sampling rate isotropic probe will allow the peak maximum RF field to be measured. If the sampling rate of the isotropic probe is not fast enough, the peak field actually being generated may be much higher that what is being displayed.

22 Future Trends  SAE EMC standard revisions are typically on a 5 year rotation.  J was published in September 2005  Next revision of this standard will begin again in the 2009/2010 timeframe.  A major change of referenced SAE standards, international standards or input of the users may justify an earlier revision.  Possible Changes:  Become a Surface Vehicle Standard?  Questions? Comments? Changes requested by Audience?

23 SAE J1113 Part 27 Electromagnetic Compatibility Measurements Procedure for Vehicle Components – Part 27 Immunity To Radiated Electromagnetic Fields – Mode Stir Reverberation Chamber Method Presented by Craig Fanning Elite Electronic Engineering Inc Automotive EMC Standards Workshop January 30 & 31, 2006 Dearborn, Michigan USA

24 Overview  SAE J specifies Radiated Immunity (Reverberation Chamber) test methods and procedures for the testing of components before they are installed in the vehicle. It is an alternative to testing in an Absorber Lined Shielded Enclosure (ALSE) radiated immunity test as described in J  The J specification covers the “Mode Stir” radiated immunity test technique.  The specification continues to be a Surface Vehicle Recommended Practice.  Corresponding International Standards: Currently there is no ISO standard for radiated immunity testing of vehicle components in a reverberation chamber. IEC was used for the basis of some of the methods described in the document.

25 Revision OF Standard  The original publication of SAE J was February  The original specification was a clone of GM 9120P.  Galen Koepke of NIST began work on the next revision of the standard in Improved procedures and formulas for the measurement of chamber performance and calculation of field generated were developed. Work on the document was halted in 2001 since the industry was leaning towards Mode Tuning and IEC was in development. At the time, J would become a Mode Tuned test method.  In 2004, a decision was made by the SAE committee to continue work on J as a Mode Stir document. A new document (SAE J ) would be developed for Mode Tuned testing based upon recently published IEC  J was then completed and published in September The revised document included much of the technical work done by Galen Koepke in

26 Test Configurations

27 Test Configurations

28 Major Changes (from the previous version)  There were many changes to the original document during the revision process. The major technical changes during this presentation.  Major Changes:  Section 3 “Definitions”:  “K Factor” (Paragraph 3.9 of original document) – This factor is no longer used nor referenced in the revised document.  “Stirrer” is now referred to as a “Tuner” in Para 3.2. The term “Tuner” is consistent with recent terms and definitions.  Definition for Chamber Quality Factor (Q) was expanded in Para 3.4 of revised document.

29 Major Changes (from the previous version)  Major Changes (cont):  “Test Conditions” was added to the document as Section 5.  This section includes:  5.1 Test Temperature and Supply Voltage  5.2 Frequency Range  5.3 Modulation (CW, AM and Pulse)  5.4 Dwell Time (One Tuner Rotation)  5.5 Frequency Steps (Linear and Logarithmic)  5.6 Test Signal Quality  5.7 Threshold of Response  5.8 Test Severity Levels (Peak Power Conservation)

30 Major Changes (from the previous version)  Major Changes (cont):  “Test Setup” now Section 6.0 of revised document  Harness length is now defined as 1.7m to 2m (previously 1m to 3m)  Setup drawings updated and improved.  “Test Procedure” now Section 7.0 of revised document. This section was completely rewritten to include:  “Preliminary System Check” Para 7.3  “Chamber Field Calibration” Para 7.4  “DUT Test” Para 7.5

31 Major Changes (from the previous version)  Major Changes (cont):  “Test Report” now Section 8 of revised document  Para 8.13 added “The (tuner) rotation rate at each frequency, as well as the method used to determine the rotation rate, must be documented in the report.”  Appendix A most of this appendix is unchanged. Points of interest:  A.1.4 “Tuner Design”: The foam board tuner shown in the original document was a tuner developed by GM. The foam board tuner remains in the revised document. A modern “Z-Fold” tuner, that is used in commercially available chambers, is also described in the revised document.  A.1.2 “Chamber Quality Factor (Q)”: formulas and A.4 “Electric Field Uniformity” formulas: Unchanged

32 Major Changes (from the previous version)  Major Changes (cont):  Appendix B:  B.1 through B.7 basically the same.  The minimum loss of the unloaded chamber is calculated in B.8 of the revised document (Previously done in B.12). Calculation similar.  “K Factor” calculation (Step B.11 of original document) has been removed. “K Factor” is no longer used.  The equivalent field strength is calculated in B.9 of the revised document (Previously done in B.8). The formula for this calculation has been changed.  B10 through B13 of revised document (Previously B13-B16) are basically the same as original document.  “K Factor” no longer referenced in Table B1 of revised document.

33 Major Changes (from the previous version)  Major Changes (cont):  Appendix C:  “Test Severity Levels” updated in accordance with SAE J and SAE J1812.  Table C2 also shows suggested test severity levels, performance criteria, and pulse modulations for Pulse Modulated testing.

34 Future Trends  SAE EMC standard revisions are typically on a 5 year rotation.  J was revised and published in September  Next revision of this standard will begin again in 2009/2010 timeframe.  A major change of international standards may justify an earlier revision.  Possible Changes:  Become a Surface Vehicle Standard?  Currently do not see any other changes. As committee receives input, changes will be considered for next revision.  Questions? Comments? Changes requested by Audience?

35 SAE J1113 Part 28 Electromagnetic Compatibility Measurements Procedure for Vehicle Components – Part 28 Immunity To Radiated Electromagnetic Fields – Reverberation Method (Mode Tuning) Presented by Craig Fanning Elite Electronic Engineering Inc Automotive EMC Standards Workshop January 30 & 31, 2006 Dearborn, Michigan USA

36 Overview  Scope SAE J specifies Radiated Immunity (Reverberation Chamber) test methods and procedures for testing of components before they are installed in the vehicle. It is an alternative to testing in an Absorber Lined Shielded Enclosure (ALSE) radiated immunity test as described in J  The J specification covers the “Mode Tuned” radiated immunity test techniques.  Corresponding International Standards: Currently there is no ISO standard for radiated immunity testing of vehicle components in a reverberation chamber. Chamber Characterization and Test methods described in the document adopted methods of IEC

37 Revision of Standard  SAE J is a new standard developed by the SAE Standards Committee. The sponsor of the document was Ronald Webb. The original publication date was November  The published specification is a culmination of test methods currently being used by Vehicle OEMS and adopts the methods of IEC

38 Test Configurations

39 Test Configurations

40 Chamber Calibration  Chamber Design and Theory are covered in Appendix A, Paragraphs A.1 through A.4.  Prior to any testing, an extensive characterization of the chamber must be performed per Appendix A and Appendix B. Calibration Procedure is discussed in Paragraph A.5. Chamber Calibration procedures are in Appendix B and C.  The chamber characterization is only performed once in the lifetime of the chamber, as long as no internal changes are made to the chamber. If internal changes are made to the chamber then the characterization must be redone.  A chamber working volume must be established as described in Para A.5.1 and as determined by Para B.1.1.

41 Chamber Calibration

42 Chamber Calibration  The calibration procedure collects Isotropic E-field probe data (maximum data only) as well as chamber input power and the maximum and mean received power from a reference antenna placed within the working volume.  The probe data is used to determine the field uniformity.  The probe data and chamber input power is used to determine the chamber calibration factor.  The mean received power from the reference antenna and chamber input power is used to determine the Antenna Calibration Factor (ACF). The ACF is used as a reference value when determining if the chamber has been “loaded” by a DUT.  The maximum received power is from the reference antenna is used to verify the probe readings.

43 Chamber Calibration  Probe data are collected from nine locations that form the corners of the “volume of uniform field” or “working volume” as shown in figure 11.  Each time the probe is moved to a new location, the reference antenna is moved to a new location within the working volume.  The orientation of the reference antenna relative to the chamber axis is also changed at least 20 degrees relative to each axis at each position. This ensures that any bias in the field is detected (e.g. no dominate polarization within the chamber).  A minimum of nine locations for both probe and reference antenna is required.  The calibration is done in log spaced frequency steps of Table B1 (see Para B3.3 of J ).  Once a chamber has been shown to operate properly over a frequency span of 300 to 400MHz at the minimum number of tuner steps (i.e. 12 tuner steps), the number of locations can be reduced to three.

44 Chamber Calibration

45 Chamber Calibration  The uniformity of the field will depend upon the number of tuner positions (N) used to collect the data. For a relatively modest number of tuner steps (i.e. 12), a reasonably uniform field can be obtained. Table A1 lists the number of tuner steps “recommended” for performing the calibration. The number of steps may need to be decreased or increased to optimize performance. The minimum number of tuner steps should not be less than twelve.  We found that 18 tuner steps provides best results.  Every chamber will have a low frequency cutoff in which it is no longer “overmoded”, and hence, it can no longer be used as reverberation chamber. The low frequency cutoff of the chamber will mostly be dependent upon the chamber size. The “undermoded” condition may be compensated for by increasing the number of tuner positions but the effects may be limited.

46 Chamber Calibration  Take the data and process it per Appendix B. There will be an enormous amount of data. The data will need to be taken with the same computer and software used to control the tuner, RF generation and RF monitoring equipment. Obtaining this data manually would probably take years.  After processing, the chamber characterization data is then used with the Formula for “Generating a Test Environment” found in Appendix A, Paragraph A 5.5  If Pulse Modulated testing is required, Appendix A, Paragraph A.5.6 must be considered.  An “Alternate Method for Determination of Chamber E-Field” is discussed in Appendix C. This is applicable where the chamber insertion loss is 10dB or greater.  Appendix D provides suggested “Test Severity Levels”

47 Additional Information – Differences Between Automotive and Other Mode Tuned Standards  The automotive standards (Ford, GM, SAE) for mode tuned radiated immunity utilize portions of IEC and RTCA DO-160E for chamber performance characterization and calibration. Formulas from IEC are used in J  The chamber performance characterization and formulas of RTCA DO-160E (Aerospace) are slightly different than IEC  The chamber performance characterization formulas of MIL-STD- 461E (Military) are different from both IEC and RTCA DO-160E.  Currently if a Mode Tuned chamber has been characterized and the formulas of RTCA DO-160 or MIL-STD-461 were used, it cannot be used for testing to the Automotive standards. If sufficient data was obtained during chamber characterization, the data can be applied to the formulas of SAE J Otherwise chamber re-characterization would be necessary.

48 Additional Information – Differences Between Automotive and Other Mode Tuned Standards  The difference for determination of E, between the Automotive and Aerospace standards, changes the chamber P input required for the same test environment.  For the same test field intensity, approximately 3dB more power must be delivered to the Mode Tuned chamber calibrated for SAE J (IEC ) than the chamber calibrated for the DO-160D/E test.  Additionally, for the same test field intensity, approximately 6dB more power must be delivered to the Mode Tuned chamber calibrated for SAE J (IEC ) than the chamber calibrated for the MIL-STD-461E test.  How do the three methods correlate with ALSE testing?  Some studies are showing a 2dB-3dB difference between ALSE and Automotive (IEC calibrated) Mode Tuned chamber test results. The calculations of DO-160E may be a better choice for improved correlation between ALSE and Mode Tuned radiated immunity testing.

49 Additional Information – Difference Between Automotive and Aerospace Mode Tuned Standards  The value E total (mean of the normalized maximum total E-field) in the equation shown in Para of DO-160E is based upon the root sum square (RSS) of the magnitude of the rectangular components at one position of the tuner.  The value for E used in Equation B1 of SAE J (also Equation A.6 of IEC ) is the average of the maximum E-Field measured by the probes normalized to the square root of the input power used during the calibration. The probe measurements used to determine the chamber E-field are the rectangular components of the probe, not the RSS.

50 Additional Information - Calculated Field with 1W into Chamber (DO-160 vs IEC)

51 Graphical Representation of 1W into Chamber (DO-160 vs IEC )  Pink – Calculated Field, DO-160 D/E Method  Blue – Calculated Field, SAE/IEC Method

52 Additional Information – Differences Between ALSE and Mode Tuned Testing  During field calibration in an ALSE chamber (SAE J ), the root sum square (RSS) value of the three axis of an isotropic probe is typically the value used for field calibration.  As previously discussed, the RSS value of the field components is not used for determination of E in the Automotive (IEC ) Mode Tuned chamber calibration.  If the DO-160D/E method for calculating E (RSS value) was used in SAE J (also Ford and GM), better correlation between Mode Tuned and ALSE Radiated Immunity methods would be achieved.  Fortunately the data obtained during a J /IEC chamber characterization can be reworked to determine the RSS value of E.

53 Additional Information – Vehicle Testing Performed to Correlate ALSE and Mode Tuned Methods  Reverberation Test Chamber DaimlerChrysler (Chrysler Group)  DaimlerChrysler has both Mode Tuned and ALSE radiated immunity capabilities at the vehicle level.

54 Additional Information – Vehicle Testing Performed to Correlate ALSE and Mode Tuned Methods  A recent study by Andrew Shune of DCC:  Found that thresholds obtained on a vehicle in a Mode Tuned chamber (IEC calibrated) were approximately 2-3dB lower than thresholds obtained on the same vehicle in the ALSE chamber.  It was determined that the difference in the test results between ASLE and Mode Tuned Chambers is that; RSS isotropic probe values are used in ALSE field calibrations and RSS values for E are not used in the IEC chamber calibrations.  From this information, the DCC chamber calibration approach:  Was simplified and achieved much better uniformity.  Demonstrated great correlation between ALSE and Mode Tuned Chamber test results.  Required much less Amplifier Power to achieve required field strength.

55 Future Trends  SAE EMC standard revisions are typically on a 5 year rotation.  J was published in November 2004  Next revision of this standard will begin again in the 2008/2009 timeframe.  A major change of referenced SAE standards, international standards or input of the users may justify an earlier revision.  Possible Changes:  Look further into the use of RSS values for calculation of E (per RTCA DO-160E) to better correlate with current ALSE field calibration practices.  Appendix D…add suggested Pulse Modulated requirements similar to J  Questions? Comments? Changes requested by Audience?