SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (412) 772-8512 FAX: (412) 776-0243TO PLACE A DOCUMENT ORDER; (412) 776-4970 FAX: (412) 776-0790http:\\Copyright 1995 Society of Automotive Engineers, Inc.3.Definitions—For general definitions, see SAE J1113-1.4.Test Equipment—The test apparatus shall consist of the following:4.1Signal Source—Any signal source and power amplifier capable of supplying approximately 50 W ofmodulated or unmodulated power to develop the immunity levels specified in the test plan shall be used, provided the following requirements are met:a.Residual FM shall be less than 10 Hzb.Frequency resolution shall be less than 100 Hzc.Harmonics and spurious outputs shall not be more than −20 dB when referred to the fundamentalpower4.2RF Voltmeter—An RF voltmeter capable of measuring 100 V up to 10 MHz.4.3In-Line directional coupler with an RF wattmeter capable of measuring 50 W up to the maximum frequency inuse.4.4Field Strength Meter—A RF field strength meter capable of measuring 200 V/m up to 200 MHz.4.5Strip line—An example construction of a strip line is shown in Appendix A.5.Test SetupCAUTION—Hazardous voltages and fields exist on and near the strip line when the equipment is energized.Test personnel should ensure that no one is in the test chamber during a test.5.1Test setup should be as shown in Figures 1 and 2.The DUT is installed next to and parallel to the strip line. The distance between the closest edges of the driven conductor and the DUT shall be 200 mm (+20 −0 mm).The distance from any peripheral device to the closest edge of the driven conductor shall be at least 200 mm. 5.2The DUT wire harness should be placed in a nonconductive fixture in the center of the strip line, parallel to itsmajor axis, supported midway between the plates. Note that the primary function of the fixture is to lock the positions of the harness and DUT to ensure the most repeatable results and should be constructed with this in mind. This non-conductive fixture shall be constructed of material with a very low dielectric constant (e.g., polystyrene or equivalent εR≤ 1.4). The length of the harness section under the active conductor shall be at least 1.5 m. Deviations of the height above the ground plane are only permitted near the DUT or the peripheral device. Peripheral devices are to be bonded to the ground plane, if possible.When peripheral devices are used for operating or monitoring the DUT, they should be the original vehicle devices, if possible. The original peripheral devices are placed on the ground plane, and electrically/ mechanically bonded to it as in the vehicle application.The power supply shall be equipped with an adequate filter to prevent overloading the front end regulator by induced RF current. The impedance of this filter, as seen from the DUT, shall correspond to the vehicle power supply system impedance as close as possible.FIGURE 1—STRIP LINE TEST CONFIGURA TIONFIGURE 2—TEST SETUP FOR A STRIP LINEThe remaining peripheral devices can be installed in one of three ways depending on their size and inherent RF immunity.a.Outside of the shielded testing chamberb.Shielded and filtered, in the shielded testing chamberc.In the case of exclusively passive periphery (resistors, capacitors, coils, ferrites, mechanical switches,etc.) or radiation resistant periphery, unshielded and unfiltered in the shielded testing chamber Lines fed through the wall of the shielded testing chamber shall be equipped with adequate RF filters at the wall. This prevents these lines from emitting significant radiation outside of the testing chamber, and possibly influencing the external measuring system, or causing other interference.5.3When a DUT or peripheral device with a metal housing used for the measurement are electrically connecteddirectly to the vehicle mass (by screws, rivets, etc.), they shall be bonded to the ground plane by a low inductance connection.When the DUT or peripheral is not electrically connected directly to the vehicle mass, they shall be placed on an insulating support. This insulating support shall be constructed of material with a low dielectric constant(e.g., foamed polystyrene or equivalent 1 ≤εR≤ 1.4) and shall have the same height as the insulating supporton which the wire harness is installed.6.Test Procedure—Three test configurations are feasible; exposure of the wiring harness alone, exposure of theDUT alone, or exposure of both the harness and DUT together.6.1Exposure of Wiring Harness Alone—This is the most commonly used test configuration permitting thewidest frequency range of testing. The RF fields induced in the harness couple into the DUT using the harness wiring as 'antennas' for the received signal. When the strip line is used above the frequency where the wavelength of the wave is less than twice the length of the strip line, the length of cable is sufficiently long to ensure that the field is 'integrated' or 'averaged' along the cable thus producing the effect of maintaining a uniform field where, in fact, it is no longer uniform.6.2Exposure of the DUT Alone—When it is desired to determine DUT immunity directly, the DUT may be placedbetween the driven portion of the strip line and the ground plane with the attached cable harness exiting at 90 degrees to the main axis of the strip line to minimize induction into the wiring harness. Care must be taken to ensure that the physical size of the DUT does not exceed 1/3 of the height between the driven element and the ground plane of the strip line as this may distort the test field.NOTE—Caution must be exercised not to exceed the frequency at which the wavelength exceeds twice the length of the strip line during this type of test as the moving peaks and nodes of the field under the stripline above this frequency may place the DUT in fields which are either much lower or much higher thaninstruments indicate, possibly producing erroneous test results. This requires special agreementbetween the users.6.3Exposure of both the DUT and its Wiring Harness—Both the DUT and its harness may be exposedsimultaneously to the field of the strip line if the provisions of the previous paragraph are taken into account.NOTE—This requires special agreement between the users.6.4Fields should be generated as required in the test plan. The field level is determined using the informationgathered from the directional coupler and power meters in accordance with the method outlined in Appendix A.For calibration purposes, at frequencies of 100 kHz or below, E v can be measured by using an RF voltmeter connected across the elements of the line. For calculation of the field under the strip line, see Appendix A. 6.5The strip line shall be excited in accordance with the frequency and modulation information supplied inJ1113-1.7.Test Severity Levels7.1 A full description and discussion of the Function Performance Status Classification including Test SeverityLevels are given in SAE J1113-1 Appendix A. Please review it prior to using the suggested Test Severity Levels presented in Appendix B.8.Notes and Special Considerations8.1For most designs of a strip line, the field strength is uniform (±2 dB) along its length up to approximately200MHz. Above 200 MHz, the uniformity degrades. The field will vary along the length of the strip line as the frequency increases. These characteristics must be considered when determining how to set up the field strength at higher frequencies.8.2Limit the size of the DUT to no more than 1/3 of the space between the active conductor and the ground plane.If this parameter is exceeded, the test field will be perturbed resulting in a stronger field than that indicated by the measured forward power.8.3Since the RF field is not fully contained, the test must be performed in a shielded room with the generating andmonitoring equipment outside the room. Energy radiated from the strip line into the shielded room will create standing wave patterns which may affect the net field strength about the test object and/or cable harness.These standing waves will be quite noticeable at frequencies where the shielded room dimensions support a cavity resonance.This effect can be reduced significantly by installing RF absorbing panels between the strip line and the walls.These panels absorb the energy radiated from the strip line (especially at frequencies where the wavelength of the frequency is more than twice the length of the strip line) and therefore reduce the influence of any reflections from the walls of the shielded room and dampen the cavity resonance effects.PREPARED BY THE SAE EMI STANDARDS AND TEST METHODS COMMITTEEAPPENDIX A(INFORMATIVE)STRIP LINE TEST THEORYA.1 A strip line sets up a region of uniform electric and magnetic fields between the ground plane and a drivenelement suspended above the ground plane. The primary usage of the strip line is to expose at least 1.5 m of the wire harness feeding the Device Under Test (DUT) to RF fields. (See Figure 1.)Because the wire harness typically is oriented longitudinally along the length of the strip line, both the E and H fields are coupled into the wire harness. (See Figure A1.)FIGURE A1—E AND H FIELD DISTRIBUTION IN A STRIP LINEThe equations for this coupling for a 377 Ω field are shown as follows:(Eq. A1)(Eq. A2)(Eq. A3)Vi 2πfhL µH ()=Vi 2πfhLx µE 377--------- =Vi E -----2h πL λ------ sin =where:Vi = Voltage Induced in lineL = Length of linef = Frequencyh = Height of harness above ground planeH = Magnetic FieldE = Electric FieldIn practice, the fields generated will be uniform only for frequencies for which the wavelength is much longer than the strip line length (i.e., the wavelength is at least two (2) times the length of the strip line). The use of a straight length of cable or harness within the strip line is required to integrate fields above the frequencies where the length of the wave is much less than the length of the harness exposed to the fields. It is also recommended that the test be performed using the actual harness, where practical, connected to the actual loads at each end. Several different lengths of harness may be used to more fully characterize the system behavior to EMI.A.2Strip Line Construction—The construction of a strip line is shown in Figures A2, A3, A4, and A5. The Ldimension shall be at least 2 m. The ratio of W to h determines the characteristic impedance according to Equation A4:(Eq. A4)where:W is the Strip line active conductor widthh is the Strip line active conductor height above the ground planeπ is approximately equal to 3.14159Given a specific example with:strip line width—W = 0.740 m.strip line height—h = 0.15 m.Equation A1 gives an impedance of Z = 50.125 Ω.NOTE—See M.V . Schneider, "Micro Striplines for Microwave Integrated Circuits," Systems Technical Journal48 #5, May-June 1969.Typical strip line fixtures are constructed to be either 50 Ω or 90 Ω with W/h equal to 5 and 1.75 respectively.Termination may be either a matched resistive load or by a tapered matching section terminated in a 50 Ωcoaxial resistive load. A resistive load can be constructed of carbon resistors, conductive strips, thick film on a ceramic substrate, etc., such that it matches the characteristic impedance of the strip line minimizing the standing waves. Both ends of the strip line should be 'tuned' using a network analyzer or time domain reflectometer to ensure a reasonably smooth match between test section of the strip line and the feed and termination points.Z 120x πW h ----- 2.420.44x h W ----- –1h W -----–6++-------------------------------------------------------------------------------------------for W/h 1.>=FIGURE A2—DIMENSIONS FOR A 50 Ω STRIP LINEFIGURE A3—FEED POINT DETAILSFIGURE A4—RESISTOR CARD TERMINATIONFIGURE A5—THICK FILM RESISTOR TERMINATIONIf the strip line is set up carefully so as to minimize reflections and maintain the system VSWR at less than or equal to 1.4:1, then only the forward power into the directional coupler needs to be measured to determine field strength. A sample calculation of strip line impedance and a plot of the field strength is shown in Figure A6. The presence of a normal wiring harness placed in the Strip line for test will not significantly alter the performance of the Strip line.NOTE—It is also necessary to measure the VSWR of the strip line with any large DUT in place.As an alternative to direct measurement of the impressed field, a calibration with an empty strip line (no harness or DUT) based upon the RMS value of the field can provide field information which will be valid for all modulations and will not be influenced by reflections from a harness or a DUT.FIGURE A6—STRIP LINE FIELD VERSUS NET POWERAPPENDIX B(NORMATIVE)TEST SIGNAL SPECIFICATIONS AND RECOMMENDED TEST LEVELSB.1Unless otherwise required in the equipment specification or approved plan, the test signals shall be setupaccording to the guidelines in SAE J1113-1. The theory of the operation of the strip line is contained in Appendix A.The suggested minimum and maximum severity levels are given in Figure B1. Testing at other levels may be chosen based on agreement between the customer and the supplier.FIGURE B1—SUGGESTED TEST LEVELSAPPENDIX C(INFORMATIVE)STRIP LINE FIELD CALCULATIONC.1The field under the driven element of the strip line is determined by measuring the forward power into thedirectional coupler and determining the field by using Equation C1:(Eq. C1)where:P is the RF power into the 50 Ω line feeding the strip lineZ is the Characteristic impedance of strip line (see Appendix A.)h is the height of active conductor above ground planeAn example of the field plot that would result from the example of a 50 Ω line is shown in Figure A6.NOTE—As a check, the strip line field below 100 kHz may be found by using Equation C2:(Eq. C2)where:E v is the Field strengthh is the height of active conductor above ground planeV rf is the RF Voltmeter reading across the septum-ground plane gapA small RF field probe may be used to verify the calculated calibration curve between the RF power into the strip line and the field in the uniform field region at frequencies below which the wavelength is less than twice the length of the strip line. The position of the field probe shall be as close as possible to the middle of the empty strip line (no harness or DUT in place) and referenced to the longitudinal and transverse axes under the strip line.Typically, the strip line field is measured only by the first method (Equation C1), which is valid over the entire frequency range. The second method (Equation C2) is only used as a check against the first.E v PxZ h --------------Volts meter ⁄=E v V rf h ------=Rationale—This SAE Recommended Practice provides a convenient method for testing automotive electronic modules and harnesses with easy access into and out of the physical test area. It is particularly suitable for small and medium size electronic components which would be difficult or impossible to test in either a Strip line or TEM cell fixture.Relationship of SAE Standard to ISO Standard—This SAE Recommended Practice is aligned with ISO Standards. The SAE through the EMI and EMR Standards Committees has been an active participant in the development of these International standards.Application—This procedure covers the recommended testing techniques for the determination of electric field immunity of an automotive electronic device. This technique uses a strip line 2 from 10 kHz to 200 MHz and is limited to exposing the harnesses (and/or devices) which have a maximum height of equal to or less than 1/3 the strip line height.This method is being replaced by the Tri-plate Line (SAE J1113-25) which is considered to be a superior test method. It will be retained for historical purposes for a period of 5 years where upon it will be considered to be withdrawn.Reference Section—For general references, see SAE J1113-1.SAE J1113-1—Electromagnetic Compatibility Measurement Procedures and Limits for Vehicle Components (Except Aircraft) (60 Hz to 18 GHz)SAE J1113-25—Electromagnetic Compatibility Measurement Procedure for Vehicle Components—Immunity to Radiated Electromagnetic Fields, 10 kHz to 500 MHz—Tri-Plate Line MethodM.V. Schneider, "Micro Striplines for Microwave Integrated Circuits," Systems Technical Journal 48 #5, May-June 1969Clayton R. Paul, "Literal Solutions for the Time-Domain Response of a Two-Conductor Transmission Line Excited by an Incident Electromagnetic Field," IEEE Transactions on Electromagnetic CompatibilityMay 1995, Volume 37, Number 2, IEMCAE (ISSN 0018-9375)Developed by the SAE EMI Standards and Test Methods Committee2.Strip line in this document refers to a giant version of an unbalanced parallel plate 'micro strip line' with a single driven plate above a groundplane. See Figure 1 for a physical description of this configuration.。
