The derivation of this formula involves considering a position in front of the antenna, on the line in the direction of radiation. The distance from this point to the edge of the antenna will be slightly more than the distance to the centre. If this distance is a significant fraction of a wavelength, the the far field pattern is not realised because of phase error / cancellation. Hence at higher frequencies (shorter wavelengths), the same position in front of the antenna will have phase errors where there were no problems at lower frequencies.
Hope this helps, Dr Luke Turnbull Principal EMC Engineer TRW Conekt Statford Road Solihull B90 4GW Tel: +44 (0)121.627.3966 Fax: +44 (0)121.627.4353 email: [email protected] web: www.trw.com/conekt/ >>> George Stults <[email protected]> 11/21/02 05:59pm >>> Hello Group, A book I've been reading gives the Rayleigh criterion for farfield conditions based on antenna (or EUT max dimension) size as dist for farfield conditions > 2*(max antenna dimension)^2/lambda When I look at this, it says that the required distance for far field conditions increases as the square of the dimensions of the antenna, which seems intuitive. What I found strange is that if you hold the antenna dimension constant, (ie for a given fixed antenna dimension) it predicts that the distance for farfield conditions will increase linearly with the frequency. That does not seem intuitive. Does anyone have a thought about how this works? Regards, George Stults WatchGuard Technologies Inc ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
