I find it reassuring to run my own antenna calibration sometimes. I set up a tuned dipole with a known impedance and input power. Then set up the antenna to be tested. Measure. It doesn’t matter which of the two antennas is the transmitter and which is the receiver. Then compare this to a NEC simulation having a dipole at both locations. And a little math and you have the AF.
Dave Cuthbert Micron Technology, Inc. _____ From: [email protected] [mailto:[email protected]] On Behalf Of Michael Heckrotte Sent: Friday, January 27, 2006 5:16 PM To: EMC PSTC - Post message (E-mail) Subject: RE: Calibrated Antenna Factor Wendy, Antenna factors vary as a function of frequency, distance, polarization, and height above the ground. The asymptotic value as distance and height get large is the free-space factor (because this is the free-space geometry). The theoretically most useful antenna factor for emissions measurements is a free-space calibration because (1) this is close to, if not perhaps equal to, the mean of all the antenna factor values over a varying range of distance/polarization/height and (2) this is theoretically the most repeatable measurement because there is no mutual coupling. However, creating true free space conditions is a challenge. Thue most useful practical antenna factor for emissions measurements is a 10 meter horizontal calibration with the receive antenna fixed at a 2 meter height above a large ground plane. According to the experts this will yield an antenna factor value within approximately 0.5 dB of the free-space value, thus it has been termed the "near free-space". It has a practical advantage of good repeatability, and is specified by ANSI C63.5-2004 as the calibration geometry to be used for emissions measurements in accordance with ANSI C63.4. Many people (years ago I was among these) reach the conclusion that better accuracy will result from using four separate factors: 10mHor / 10mVert / 3mHor / 3mVert. The problem is that when emissions are maximized at some antenna height that is different from the height at which the antenna was calibrated, there is still a significant residual error. In fact, this error can actually be greater than the deviation from the free-space value or the near free-space value because the calibration geometries that have more mutual and/or ground plane coupling (Closer distances / Vertical polarization / Lower heights above the ground plane) will exhibit wider deviations from the free-space value at a more frequencies. Calibrations for NSA measurements are a different story, and this topic is covered in Annex F of ANSI C63.5-2004. It is recommended that you recalibrate your antenna at the standardized near free-space condition. Best Regards, Mike Michael Heckrotte Engineering Manager, CCS (408) 463-0885 ext. 121 fax: (408) 463-0888 [email protected] From: [email protected] [mailto:[email protected]]On Behalf Of wendy Sent: Thursday, January 26, 2006 6:41 PM To: [email protected] Subject: Calibrated Antenna Factor I have just purchased a new bilog antenna. It was calibrated at a 3m site and gave only horizontal Antenna Factor. Can I use the AF for a 10m measurement? And do I assume the horizontal and vertical AF is the same? Any quick advice? Regards, Wendy Nya LabOne Singapore - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
