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Free Space Antenna Factors Through the Use of Time-Domain Signal Processing

The term free-space implies that there is no electromagnetic interaction between the test environment and the antenna. Use of the time domain to separate spacial effects allows for determination of the environment or the antenna without influences of the other. A recent paper on this topic was presented, and selected as best symposium paper, at the 2007 IEEE International Symposium on EMC. The paper [1], titled “Free Space Antenna Factors through the use of Time-Domain Signal Processing” by Dennis Camell, Robert Johnk, David Novotny and Chriss Grosvenor of the National Institute of Standards and Technology (NIST), describes a process to determine free space antenna factors using the standard site method (SSM) without the accompanying facility effects. Time domain gating routines, usually built into a vector network analyzer (VNA), can be used to remove the reflected signals of the facility thus providing a free-space environment for the antenna. This process provides excellent results above 1 GHz and good results for some cases below. This method allows for improved accuracy in the determination of free-space antenna factors. Finally, this method fits well with current EMC standards methods.

ANSI ASC C63®, a US national standards committee on EMC, has working groups that are leading efforts to include time domain measurement methodology in EMC standards.
This includes both the antenna area with the revision of the ANSI C63.5 standard and in site acceptability with a new standard, C63.25. These working groups are always looking for new members to help in this work.

Visit or contact Don Heirman at for more information. Better yet, attend the next series of ANSI C63 meetings which will be held in New Brunswick, NJ at IEEE Headquarters the week of April 19, 2010. Contact the Subcommittee 1 Secretary, Janet O’Neil, for meeting information at j.n.oneil

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  1. Free-Space Antenna Factors through the Use of Time-Domain Signal Processing, Camell, D., Johnk, R.T., Novotny, D., Grosvenor, C., 2007 IEEE International Symposium on EMC, July 9-13, 2007, pp 1-5.


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