I understand about the beamwidth issue as it relates to covering the 1.5x1.5m area. What I was referring to was the chamber performance. If the beamwidth is enough to cover the 1.5x1.5 UF, but drops off quickly outside that, then the performance of the anechoic material on the side walls/floor/ceiling is not really being tested. An isotropic radiator would be, in my mind, a better measure of the chamber performance as it relates to uniformity. I know you would not want to use an isotropic radiator for testing products, but for the chamber performance check I think it would be worst case. On another note, years ago I was involved with the purchase of a horn antenna for radiated immunity testing above 1ghz. The gain was higher than other antennas I looked at. At 1ghz it was great, but above about 3ghz the beamwidth narrowed enough that I could not get uniformity. Above 4ghz the outside corners of the 1.5m square UF were below the noise floor of the probe. :-( I learned my lesson on that one. Bob R.
--- On Thu, 8/26/10, Jason Smith <[email protected]> wrote: The directivity of the antenna could play a role if the chamber’s performance was not the best. The antenna does play a huge role in what the uniform field is and what power is required to reach field. Most bicon and biconilog antennas are poor choices for RI since they use a balun to match the antenna which is a source of lost power. You need a broad beam width to cover the 1.5x1.5m widow at 3 meters which is not to much an issue below 1 GHz but is a concern above this. The right antenna selection makes all the difference. The best solution is an LP that covers 80-1GHz and ether a stacked LP or a double ridge horn to cover above this. A minimum 3dB beam width of 30degres is needed through the frequency range. Thank you, Jason H. Smith ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Bob Richards Sent: Thursday, August 26, 2010 10:11 AM To: [email protected] Subject: Re: Field Uniformity Calibration per 61000-4-3 What would be considered worst case? A bicon - log periodic pair, or a bilog hybrid? I think the less directional the antenna, the worse the uniformity may be, but, I'm no expert on antennas. Bob R. --- On Thu, 8/26/10, John Woodgate <[email protected]> wrote: From: John Woodgate <[email protected]> Subject: Re: Field Uniformity Calibration per 61000-4-3 To: [email protected] Date: Thursday, August 26, 2010, 2:57 AM In message <1347744851.367114.1282781476042.javamail.r...@sz0149a.emeryville.ca.mail <http://us.mc565.mail.yahoo.com/mc/compose?to=1347744851.367114.1282781476042.javamail.r...@sz0149a.emeryville.ca.mail> .comcast.net>, dated Thu, 26 Aug 2010, [email protected] <http://us.mc565.mail.yahoo.com/mc/[email protected]> writes: > Shouldn't the chamber user's antenna be used for the field-uniformity test? Otherwise I don't see how the results would apply if a different Tx antenna is later used. The radiation cahracteristics, including the coupling with the chamber, will be different. I think so, too, but there are possibly two stages: - check the chamber for freedom from non-uniformity [1] using a reference antenna; - check that acceptable uniformity can be achieved with the user's antenna. [1] e.g. due to one or more quasi-specular reflections. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK If at first you don't succeed, delegate. But I support unbloated email http://www.asciiribbon.org/ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <http://us.mc565.mail.yahoo.com/mc/[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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To post a message to the list, send your e-mail to <[email protected] <http://us.mc11.mail.yahoo.com/mc/[email protected]> > All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <http://us.mc11.mail.yahoo.com/mc/[email protected]> > Mike Cantwell <[email protected] <http://us.mc11.mail.yahoo.com/mc/[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <http://us.mc11.mail.yahoo.com/mc/[email protected]> > David Heald <[email protected] <http://us.mc11.mail.yahoo.com/mc/[email protected]> > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
