Evaluation Engineering - December 2008 - (Page 47)

labs are willing to share ILC results with their customers upon request. Current Status of ANSI C63.5 by Dennis Camell, NIST and the ANSI-ASC C63® Subcommittee 1 Revisions to ANSI C63.5 Changes and improvements have been made to ANSI C63.5 from the first publication in the 1980s. The most recent editions were in 1988, 1998, 2004, and 2006. In the present edition, the most notable addition was that speciﬁed biconical antenna calibration data should be reported as NFSAF and corrected to FSAF to be used for product testing and Normalized Site Attenuation (NSA) measurements. The NSA calibration requires that geometry-speciﬁc antenna factors be added to the FSAFs. In general, the 2006 standard provides a means of measuring antenna factors for most types of antennas used in emissions testing. The parameters speciﬁed for the calibration are horizontal polarization at a separation distance of 10 meters and a transmitting antenna height of 2 meters, and the receiving antenna search heights are from 1 to 4 meters. Other key provisions of the 2006 version include the following: • The antenna factors can be used for either vertically or horizontally polarized measurement at separation distances of 3 meters or more. • Calibration measurements at 3 meters included in previous versions of ANSI C63.5 were considered unacceptable and removed. • Previous versions of ANSI C63.5 included information on calibration using vertical polarization; this was removed. • The SSM based solely on horizontally polarized measurements provides one antenna factor that is used for both polarizations from 30 MHz to 40 GHz. • Antenna factors obtained for biconical antennas are NFSAF; the standard requires they be corrected to FSAF using the correction factors provided in Table G.1 of the standard. • Biconical antennas used for NSA measurements will be calibrated at a 10-meter separation, horizontal polarization, and then Table G.1 www. ev alua t ion e n gin e e rin g.com ANSI C63.5-2006: American National Standard for Electromagnetic Compatibility– Radiated Emission Measurements in Electromagnetic Interference (EMI) Control–Calibration of Antennas (9 kHz to 40 GHz) provides methods of calibration for antennas used in EMC measurements. While this version has addressed issues of concern in the past and incorporated technical advances, several items are proposed for the next revision. Since 2006, a working group in Subcommittee 1 of ASC C63® has been developing the next revision. This group is composed of knowledgeable individuals whose work is related to the use of this standard. Changes to this standard are done periodically to improve understanding, promote comprehension, incorporate technical advances, and correct mistakes since the last version. The time needed for a complete revision cycle is minimally two years. There are several sources for these changes including feedback from the users of the document and harmonization with similar national and international standards. When technical advances are made, they, too, are incorporated into the standard. Corrections to any typographical errors and clariﬁcations of existing text and ﬁgures are a continual component in the revision cycle. In this current cycle, about onethird of the proposed changes relate to clariﬁcations and additions to existing text or typographical corrections. Approximately onefourth of the current work is related to harmonization with other standards, and the remaining changes address technical advances with EMC antenna measurement methodologies. The last revision had a large change relating to FSAF and GSCF and included an informative annex on measurement uncertainty. Additional text is proposed in the next revision to improve the understanding of these concepts and the explanation of their usage. Discussion on standard gain horns and their requirement for calibration is ongoing and will result in more speciﬁc requirements for this antenna type. Several text additions for clariﬁcation and ease of use include a Table 3 redesign, addition of the Edmax equation for vertical polarization into Annex A, and speciﬁcation of the minimum frequency resolution. An expansion of the calibration site correction table similar to the present annex G for biconicals will be included for dipole antennas in the next revision. Also, new are an option for timedomain gating to achieve free-space results, a use for complex-ﬁt NSA for log-periodic antennas to account for speciﬁc geometries, and a limitation on the antenna type for NSA based on the maximum variation in the comparison of vertical to horizontal NSA. Finally, the description of measurement uncertainty may be moved into the upcoming ASC C63® uncertainty standard which has been given the number ANSI C63.23. This is in draft form and will not be available before mid 2009. The completion of this revision of ANSI C63.5 is targeted for 2009. While overall goals are currently scripted, details still are being molded by the ASC C63® Subcommittee 1 working group on antenna calibrations. If you have comments on these topics or wish to assist in the development of this standard, contact ASC C63®. This U.S. national standards committee always welcomes new members that have an interest in seeing this standard or its other standards developed with new and accurate details in a timely manner. will be used to obtain the FSAF. Table G.2 or Table G.3, which lists the GSCF, is used together with the FSAF in performing normalized site attenuation measurements (30 MHz to 200 MHz). It is important to note the frequency limitation. Continued on page 48 December 2008 • EE • 47 http://www.evaluationengineering.com

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Evaluation Engineering - December 2008

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