7/19/2002 Kenneth John Webb Page 1 COMPARING EMISSION MEASUREMENTS IN A REVERBERATION CHAMBER AND A SEMI-ANECHOIC CHAMBER By Kenneth John Webb Principal EMC Engineer

7/19/2002 Kenneth John Webb Page 2 Agenda Purpose of Project Overview of Project Dipole Data Laptop Data Summary and Conclusions

7/19/2002 Kenneth John Webb Page 3 Purpose of Project Validate Reverb Chamber (RC) Calibration To define a possible test method for performing emissions in a RC Comparing results in a RC to conventional test results in an Anechoic Chamber (AC) Determine if equation is valid –Power density to V/m equation –Use of CCF, ACF, IL, CLF defined later

7/19/2002 Kenneth John Webb Page 4 Overview of Project Perform Calibration in RC Test a known source Test in RC and AC Calculate E-field using different techniques Validates method Test and unknown source Test in RC and AC Use methods derived on known source

7/19/2002 Kenneth John Webb Page 5 Why Measure Emissions in a Reverb Chamber? New Robust Test Method –Test all sides of the unit Cost of reverb chamber is less than conventional anechoic rooms Measure total fields emanating from unit Test systems without multiple antenna positions or unit orientations Less setup time from susceptibility testing to emissions testing

7/19/2002 Kenneth John Webb Page 6 Emissions in Reverb Chamber

7/19/2002 Kenneth John Webb Page 7 Reverb Chamber Physical Characteristics

7/19/2002 Kenneth John Webb Page 8 Typical Tuner

7/19/2002 Kenneth John Webb Page 9 Calibration Summary Meets the calibration requirements of DO-160D Change 1 from 400MHz to 18GHz. Uniformity is marginal from MHz, the allowed standard deviation is acceptable. Above 1 GHz, chamber uniformity is acceptable. Antenna vs probe exceeds the allowed +/-3 dB tolerances using the log periodic antenna. –Using the EMCO 3106 antenna from 400MHz to 2GHz allowed acceptable results Obtained calibration factors needed for emissions testing

7/19/2002 Kenneth John Webb Page 10 Emission Comparison Methodology

7/19/2002 Kenneth John Webb Page 11 Emission Comparison Use data collected in calibration for CCF, ACF, CLF,and IL Use equation given in IEC for power density to E-field conversion Measure a known source (dipole antenna) and an unknown source (Laptop computer) Use basic test methods in AC Develop a new method for RC

7/19/2002 Kenneth John Webb Page 12 Dipole Testing

7/19/2002 Kenneth John Webb Page 13 Dipole Antenna Estimated 127dBuV/m with +20dBm –Signal generator not linear, but used same one for both AC and RC tests AC will use conventional method –Use AF –Place RCV antenna in H and V polarities –Dipole in H only RC new method –No direct illumination

7/19/2002 Kenneth John Webb Page 14 Dipole Antenna in AC

7/19/2002 Kenneth John Webb Page 15 Dipole Antenna AC Data

7/19/2002 Kenneth John Webb Page 16 Dipole Antenna in RC

7/19/2002 Kenneth John Webb Page 17 Summary of Equations

7/19/2002 Kenneth John Webb Page 18 Dipole Antenna RC Data E Radiated (V/m) is the estimated field strength produced by the dipole antenna R was assumed to be 1m since the final measurement is in volts per meter. D is the equivalent directivity of the dipole. –Determining the correct value would be an interesting experiment. For the purposes of this paper, 1.7 was used. Power into antenna was not linear –Same signal generator was used for both anechoic and reverb chamber data Tx, Rx = the antenna efficiency factors for the transmit and receive antenna respectively –Used 0.75 for a log periodic antenna and 0.9 for a horn antenna

7/19/2002 Kenneth John Webb Page 19 Antenna Calibration Factor Equation Needed for emissions calculations for max power radiated Takes into account the antenna losses, gain, and efficiency

7/19/2002 Kenneth John Webb Page 20 CCF CCF or Chamber Calibration Factor from eqn CCF is the normalized average received power P AveRec is the average received power over one tuner rotation P Input is the forward power averaged over one tuner rotation. Used emission field level calculations for average recevied power

7/19/2002 Kenneth John Webb Page 21 ACF and CLF The chamber loading factor (CLF) is calculated using equation CCF is from equation ACF is from equation Also used for emissions level calculations –Used with Insertion Loss equation for max received power

7/19/2002 Kenneth John Webb Page 22 IL IL is from equation Also used for emissions level calculations –Use with max radiated power IL is the normalized maximum received power –Calculated during calibration

7/19/2002 Kenneth John Webb Page 23 Dipole Antenna RC Data, No CCF applied

7/19/2002 Kenneth John Webb Page 24 Dipole RC and AC Data No CCF

7/19/2002 Kenneth John Webb Page 25 Dipole RC Data Retest The retest data collected was for information only Performed manually using mode stirred approach Verify data collection techinique

7/19/2002 Kenneth John Webb Page 26 Dipole RC Data Retest, No CCF applied, Mode Stirred

7/19/2002 Kenneth John Webb Page 27 RC Dipole Data with CCF or CLF/IL

7/19/2002 Kenneth John Webb Page 28 RC Dipole Data with CCF, AVG to MAX

7/19/2002 Kenneth John Webb Page 29 RC Dipole Data with CCF AC and RC Data

7/19/2002 Kenneth John Webb Page 30 RC Dipole Data with CCF dB Delta

7/19/2002 Kenneth John Webb Page 31 RC Dipole Data with CCF dB Delta

7/19/2002 Kenneth John Webb Page 32 Dipole Summary Excellent correlation. –2dB delta between rooms for the dipole measurements can be considered validation of the test method. Use the RSS or MAX of the horizontal and vertical polarities –Must use CCF for AVG Power –Use CLF and IL for MAX power Retest RC data with mode stirring also has good correlation to AC –Verifies mode stirring technique using equation for average power

7/19/2002 Kenneth John Webb Page 33 Dipole Summary: Tuned or Stirred?

7/19/2002 Kenneth John Webb Page 34 Laptop Testing

7/19/2002 Kenneth John Webb Page 35 Laptop Setup in AC

7/19/2002 Kenneth John Webb Page 36 Laptop Setup in AC

7/19/2002 Kenneth John Webb Page 37 Laptop Setup in AC

7/19/2002 Kenneth John Webb Page 38 Laptop Setup in AC

7/19/2002 Kenneth John Webb Page 39 Laptop Setup in RC

7/19/2002 Kenneth John Webb Page 40 Laptop Setup in RC

7/19/2002 Kenneth John Webb Page 41 Sample Laptop Data RC

7/19/2002 Kenneth John Webb Page 42 Laptop Data in RC with CCF

7/19/2002 Kenneth John Webb Page 43 RC Laptop Data CCF vs CLF

7/19/2002 Kenneth John Webb Page 44 Ambient in RC with CCF

7/19/2002 Kenneth John Webb Page 45 Laptop RC Data Ambient is a concern –RS testing may be leaking RF –50MHz emissions for info only CCF vs CLF about 5 to 10dB different Used both to compare the data

7/19/2002 Kenneth John Webb Page 46 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 47 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 48 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 49 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 50 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 51 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 52 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 53 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 54 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 55 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 56 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 57 Laptop Measurements in AC

7/19/2002 Kenneth John Webb Page 58 AC vs RC CCF Laptop Data

7/19/2002 Kenneth John Webb Page 59 RC CCF vs AC Data

7/19/2002 Kenneth John Webb Page 60 RC CCF vs AC Data Delta

7/19/2002 Kenneth John Webb Page 61 RC CCF vs AC Data Delta

7/19/2002 Kenneth John Webb Page 62 RC CCF vs AC Data

7/19/2002 Kenneth John Webb Page 63 RC CCF vs AC Data

7/19/2002 Kenneth John Webb Page 64 RC CCF vs AC Data

7/19/2002 Kenneth John Webb Page 65 RC CCF vs AC Data

7/19/2002 Kenneth John Webb Page 66 AC vs RC CCF Laptop Data

7/19/2002 Kenneth John Webb Page 67 RC CLF vs AC Data

7/19/2002 Kenneth John Webb Page 68 RC CLF vs AC Data

7/19/2002 Kenneth John Webb Page 69 RC CLF vs AC Data

7/19/2002 Kenneth John Webb Page 70 RC CLF vs AC Data

7/19/2002 Kenneth John Webb Page 71 RC CLF vs AC Data

7/19/2002 Kenneth John Webb Page 72 Conclusions Laptop data not as good a correlation as the dipole data –The maximum AC data was the best correlation to the RC CCF or CLF data for the Laptop –The RSS or MAX was the best for the dipole Several spikes that were within 10-20dB of each other for the Laptop data –The dwell time of 50ms may not have been long enough to capture the full amplitude. –May be due to dwell time of RC data –Tuner speed may need to be increased/decreased –Use of MAX vs AVG equations for E-field

7/19/2002 Kenneth John Webb Page 73 Conclusions Assumption that the Laptop rotation (in six different orientations) could be correlated to the reverb chamber data may be incorrect. –A Laptop orientation (other than the 90 degree changes) may have a higher amplitude emissions. The frequency accuracy may also have been different between the two test methods. –Frequencies may have been off –The tuner may modulate the emissions and change the frequency slightly.

7/19/2002 Kenneth John Webb Page 74 Conclusions The method for performing the test and the equation used to calculate the E-fields does appear to have an overall correlation and usefulness. –Generally, the RC had a higher amplitude when using average power equation and mode-stirring –Data trend was similar –Dipole measurements within 2dB Future testing is definite –Spherical dipole radiator – Different dwell/sweep times

7/19/2002 Kenneth John Webb Page 75 Questions??