Conformity - November 2008 - (Page 13) ethods for calibrating antennas have been around since antennas were first used. Over the years our understanding of antennas and their performance in their intended applications has continued to evolve. In this article we seek to discuss the past, present, and future state of our antenna calibration work in the Accredited Standards Committee C63® (ASC C63®), which has resulted in the publication of the American National Standard, C63.5 “Radiated Emission Measurements in Electromagnetic Interference (EMI) Control–Calibration of Antennas (9 kHz to 40 GHz).” This work is performed by experts in ASC C63® which maintains the currency of ANSI C63.5. Don Heirman, chairman of ASC C63®, believes that this article presents a major step forward in the understanding of what ASC C63® has and will be doing in bringing the latest theory and technology forward in the antenna calibration area. He also believes that ASC C63® is in a unique place to support this work, as its membership is from industry, regulatory bodies, military, universities, and consultants located in the U.S. It is this broad representation that lends itself to robust standards such as ANSI C63.5 as it is reviewed by the committee membership. This then lends itself to provide its expertise to the work being done internationally in the Special International Committee on Radio Interference (CISPR). M This article leads the reader through the history of the work on ANSI C63.5, from its beginning to the latest version that was published in 2006, and on to the future. Historical Roots The predominant method currently used to calibrate antennas in the frequency range of 30-1000 MHz is based on the work of Albert Smith [1] dating back to the early 1980s when he provided his expertise in ASC C63®. A companion article was published at the same time by Smith et al [2] on the calculation of normalized site attenuation using antenna factors. Together, these articles interlaced antenna calibrations and site attenuation for the foreseeable future. Figure 1 shows a photo of the late Al Smith. There is an explicit recognition in [1] that the antenna factors measured using the standard site method depend on the site attenuation with the quote “The standard-site method of determining antenna factors is based on site attenuation measurements made on a near ideal, open-field site.” However, how do we determine if a test site is a near ideal site? Answer: By measuring the site using antenna factors! This catch 22 scenario has always been a source of concern in some parts of the EMC community. Nonetheless, efforts have been made through the standards process to reconcile this concern. Figure 1: The late Al Smith is shown in his office at IBM. Mr. Smith’s paper “Calculation of Site Attenuation from Antenna Factors,” coauthored with R. F. German and J. B. Pate, was recognized as one of the top ten “Most Referenced” Transactions papers in the 50-year history of the IEEE EMC Society. november 2008 Conformity 13 http://www.captorcorp.com http://www.captorcorp.com http://www.captorcorp.com
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