Hello Cody, The answer is yes with some limitations.
The correlation algorithm used in IEC 61000-4-20 models the EUT as a dipole. This model works quite well, when you have a battery-powered EUT and the largest dimension of your EUT is smaller than or equals the wavelength of the highest frequency measured. Having an EUT with larger dimensions, cables etc. increases the directivity at the upper end of the frequency range and a lack of precision in cable positioning leads to larger variations in the lower frequency band. All this leads to larger differences between GTEM and OATS when stretching the limit imposed in IEC 61000-4-20. >From my personal experience, I can tell that there can be larger differences with large EUTs, but the GTEM cell (at least a large one) is not that unforgiving and deviations from the standard in cable positioning do not necessarily lead to larger deviations in the correlated results when comparing the measurement of the very same EUT with one using an OATS. On the other hand - OATS, FAR and SAR have their limitations as well. The GTEM cell measurement provides data about the radiated power which is converted into field strength using the algorithm in the standard. Measurements using an OATS or SAR, provide data about the field strength on an imagined cylinder surface with 10m radius, extending from 1m to 4m above the ground plane and its mirror image through the ground plane. Using a FAR, you only see the upper cylinder surface. In both cases, narrow beams which do not 'hit' these imagined cylinder surfaces will not be seen at their maximum level. Best regards, Michael Nagel Michael Nagel Senior Staff EMC Test Engineer Embedded Computing Emerson Network Power T +49-89-9608-0 F +49-89-9608-2376 [email protected] www.emersonnetworkpower.com/embeddedcomputing Emerson Network Power - Embedded Computing GmbH, Lilienthalstr. 15, D-85579 Neubiberg/Landkreis München, Deutschland / Germany. Geschäftsführer Josef Wenzl, Amtsgericht München HRB 171431, VAT/USt.-ID: DE 127472241 From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Freitag, 3. Juli 2009 19:06 To: [email protected] Subject: Correlating GTEM data with OATs I am trying to understand how to properly use TEM and GTEM cells to take radiated emissions data. Has anyone had any success in correlating far field radiated emissions measurements with GTEM measurements? Thanks, Cody - 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]> - 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]>
