Test Artifact For Radiated Immunity

Description

The test artifact illustrated above is used to support proficiency testing for the Tri-Plate Line Method listed per the Automotive EMC Laboratory Recognition Program (AEMCLRP).  Information regarding both operation of the artifact in addition to its construction are presented below.  Note that while any laboratory may construct this test artifact, only artifacts supplied by the OEM may be used as during the accreditation process per AEMCLRP.

Theory of Operation

The test artifact is very simplistic device that is designed to sense induced currents that flow on a DUT and its attached cable when exposed to an incident electromagnetic field.  The figure below illustrates the basic circuit.  The copper plate represents the DUTs internal printed circuit board.  The coaxial cable (RG 223U) represents the DUT's attached cable harness. When the artifact is exposed to an electromagnetic field, the current I_W is induced on the copper plate and and the outer conductor of the coaxial cable.  The current divides between the sensing resistor R_S and load impedance R_L.  The artifact output,  measured in dBm into  R_L is proportional to the value of I_W at the sensing resistor R_S. 

223

Construction The test artifact is composed of three primary elements: Copper Plate Assembly Coaxial Cable Termination Box Coaxial Attenuators The copper plate assembly consists of a two layer copper FR4 printed wiring board which contains eight, half watt 82.5 ohm resistors (+/-1%), connected in parallel to yield an equivalent resistance of 10.3 ohms.  Figure 2 shows the actual copper plate assembly.   Copper Plate Assembly Top Layer Bottom Layer   Coaxial Cable The cable connecting the copper plate assemble to the termination box consists of RG 223 coaxial cable (50 ohm, double shielded) fitted with a right angle Type N connector on one end and a SMA connector on the other.  The cable length is approximately 2 meters in length. Termination Box The Termination Box is used to terminate the the coaxial cable assembly the Tri-Plate Line's ground plan.  It also facilitates connection of instrumentation to measure the artifact output during testing.  The proficiency testing procedures delineated in Appendix J of the AEMCLRP document calls out two different test methods, Procedure 1 and Procedure 2.  Procedure 1 requires connection of an RF tunable receiver to the output of the artifact to measure the output power PL at each test frequency.  The Termination Box contains a simple pass through cable to facility direct connection of the RF receiver.  Procedure 2 is similar to Procedure 1 except the artifact cable is connected to an RF diode detector which will produce a DC voltage proportional to the RF signal.  For this procedure, the RF tunable receiver is replaced by a DC volt meter with measurement capability below .1 mV.  The primary reason the diode detector is used is to sense both the intended coupled signal plus any spurious and/or harmonic content from the RF source connected to the Tri-Plate Line.  The Termination Box's internal configuration is illustrated below:       Note that pass through cable shown in that actual photo above is longer than that depicted in the drawing above it.  There is no particular reason for this other than to make sure the cable was long enough to fully engage the SMA/Type N adaptor.  Shorter lengths may be used and but it is not necessary to worry about the attenuation differences which will be less than 0.1 db. The low pass RC filter on the output of the diode detector is present to reduce noise in the output measurement at lower frequencies.  Tolerances for components were 5% for the resistor and 20% for the ceramic disk capacitor. Note that the diode detector used is the Agilent 8473D which is quite expensive.  The primary reason for the selection of this specific device is because all 8473Ds are matched to each other resulting in consistent measurement results which  greatly simplifies the task of characterization for multiple artifacts. Coaxial Attenuators The attenuators are inserted between the artifact coaxial cable and the Termination box. They are used to provide an improved 50 ohm termination and to protect measurement receiver and the diode detector.  There are two attenuator values; 3db for the 25 V/m test and 20 db for testing at 200 V/m.

Test Artifact Part Description

The table below lists all of the parts necessary to construct the test artifact described above.  Note that the for the copper plate assembly.  The Gerber files are available for download to facilitate fabrication.