Everyday radiated emissions measurements above 1 GHz are being made on products. These measurements bring a unique set of challenges. The higher the frequency being measured, the narrower the beamwidth. This results in the signals being harder to find in the preliminary scans, harder to maximize, greater errors from ground plane imperfections, etc. Should these emissions be measured in an open area test site (OATS), anechoic room, reverberation chamber, or GTEM? What types of antennas are the most efficient and accurate? Should we use receivers or spectrum analyzers? What are the uncertainty contributions at these frequencies and test setups? All these questions and problems are part of the research underway to revise our measurement standards. They were also the topics of an exciting afternoon workshop by the IEEE EMC Society at the 14th International Zurich Symposium and Technical Exhibition on EMC February 20-22, 2001. The title of the workshop was "EMC Measurements Including those Above 1 GHz and Associated Uncertainty."
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Speakers at the IEEE EMC Society special workshop in Zurich included (front row left to right) Dr. Pierre Beeckman of Philips, Dennis Camell of NIST, Ed Bronaugh of EdB EMC Consultants, Ghery Pettit of Intel, (back row left to right) Bob Johnk of NIST, Mike Windler of UL, and Don Heirman of Don HEIRMAN Consultants. |
The master of ceremonies for the afternoon was Don Heirman of Don HEIRMAN Consultants, Lincroft, New Jersey. This was only fitting since it was Don that proposed the afternoon workshop and coordinated the development of the papers and presentations.
Ed Bronaugh of EdB™ EMC Consultants, Austin, Texas, was the lead off speaker discussing measurement instrumentation used for measurements above 1 GHz. Ed's talk delved into a wide variety of instrumentation from spectrum analyzers and receivers to amplifiers and antennas. Proper pass band filters, high quality low loss cables and instrument settings were discussed in detail. Ed's review of the instrumentation issues was warmly received.
Next up on the workshop agenda was an article by Dennis Camell of the National Institute of Standards and Technology (NIST) RF Technology Division, in Boulder, Colorado, and Mike Windler of Underwriters Laboratories, in Northbrook, Illinois. They examined the issues and potential problems of various antennas used above 1 GHz. Dennis gave the presentation to a rapt audience. The presentation reviewed the current antenna requirements in ANSI, CISPR, and ETR. The plots of the principal plane patterns, beamwidths, cross polarization characteristics of various antennas including log periodic dipole arrays, double ridge horn standard and octave gain horns were presented.
Dennis also collaborated with colleagues, notably Dr. Robert Johnk of NIST and Ken Hall of the Hewlett-Packard Company, in Roseville, California, in presenting a paper on exploring test site performance using a double ridge horn. Thanks to their efforts, the audience learned that using the traditional normalized site attenuation methods would result in virtually any site complying! Even with a sheet of steel just a few meters to the side of a measurement path, no reflections were detected. This research clearly demonstrated the need for more analysis to develop a meaningful site qualification procedure that is representative of the measurement process.
If one thing is certain, it is that Ed Bronaugh's talk on measurement instrumentation uncertainties was educational. Influence quantities of receiver versus spectrum analyzer configurations were compared. Different antennas, measurement environments and cable types were also contrasted with respect to measurement uncertainty. Ed summed it all up nicely!
The current state of affairs with draft international standards on measurement uncertainty being developed in the International Special Committee on Radio Interference (CISPR) was thoroughly reviewed by Don Heirman. Don's insights were excellent, as you might have guessed. The extensive activities of both CISPR and the US Accredited Standards Committee C63 working groups were reviewed in detail. Radiated emission measurement uncertainty proposals under consideration by both organizations were examined. The international efforts to create practical requirements for measurements above 1 GHz and the associated uncertainties are indeed far-reaching.
Uncertainties were sure to come up again as Pierre Beeckman of Philips Research in the Netherlands took the stage. Pierre provided an overview of the contributions to uncertainty from the equipment under test and the test setup requirements in standards.
The lack of guidance in the current standards contributes to uncertainty by not providing enough guidance in test setups, cable manipulation, etc. Pierre's presentation tied together the issues of calibration, errors, and instrumentation uncertainty from Ed's presentation on uncertainty.
The closing speaker for the afternoon workshop was Ghery Pettit of Intel in Dupont, Washington. Ghery discussed the nature of emissions from products that occur above 1 GHz. Proper measurement of spread spectrum clock signals utilized in computers and telecommunications equipment was reviewed. Some of the practical difficulties of finding millimeter wavelength emissions during preliminary scans in an OATS environment were also considered.
Instrumentation, antenna selection, instrumentation uncertainties, site qualifications, set-up uncertainties, standards developments, and the complexities of practical measurements are a lot to cover in one afternoon. The IEEE EMC Society special workshop in Zurich covered them all. It was a big hit with over 100 people in attendance! Yet more work is being done. Research is underway under the auspices of ANSI Accredited Standards Committee C63 and CISPR Subcommittee A to develop a practical way of evaluating a test site for reflections. Beamwidths of products and antennas are being studied to determine the feasibly of using reverberation chamber test techniques and establishing emissions measurements in terms of radiated power. The practical frequency limit to manually pre-scanning products is also under consideration. With all this work underway, you can expect more interesting and educational presentations to come from the IEEE EMC Society.
For further reading, the presentation slides used for this special IEEE EMC Society workshop are included in the Zurich Symposium proceedings – view the website for ordering information on https://www.emc-zurich.ch/ or contact Dr. Gabriel Meyer at gmeyer@nari.ee.ethz.ch . Those interested in pursuing this topic further are encouraged to join the Working Groups in ANSI ASC C63 Subcommittee 1 on "Measurement Techniques and Methods." Visit the website https://www.C63.org for more information. Or, consider joining the Technical Advisory Groups in your respective countries for CISPR. Visit the website https://www.iec.ch which provides information on CISPR activities.
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Michael J. Windler is an Associate Managing Engineer responsible for the operation of the EMC laboratory of Underwriters Laboratories Inc. in Northbrook, Illinois. Mr. Windler is an active member of the American National Standards Institute Accredited Standards Committee C63 (ANSI ASC C63). In addition, he is a member of the ANSI ASC C63 Subcommittee 1 on "Measurement Techniques and Methods" as well as Subcommittee 6 on "Laboratory Accreditation." Mr. Windler is also the chairman of the ANSI ASC C63 working group 1-13.2 on "Requirements for Sites Operating above 1 GHz." He was also a principal researcher in the development of correction factors for biconical antennas under working group 1-15.6. He earned a BSEE from the University of Wisconsin and an MBA from Northwestern University. EMC