Consider how the reflected wave from the ground plane at the 10m site might add or subtract to the incident wave depending on frequency and antenna height. Also, the near-field probe measurement is taken in the near-field (obviously) while the antenna at the 10m sight is in the far field. Also, your results with the near-field probe will depend on probe orientation and distance held from the product.
-----Original Message----- From: Bronaugh, Edwin [mailto:[email protected]] Sent: Thursday, September 14, 2000 5:10 PM To: '[email protected]'; [email protected] Subject: RE: Near Field Versus Far Field Mr. Martin, have you thought about the fact that the near-field probe does not integrate the whole radiation sphere from your product? On the 10 m site, your antenna sees radiation components from all parts of the EUT, including any cables; while your near-field probe in the lab cannot pick all of these up at the same relative levels and phases as does the antenna on the OATS. This may not be your problem, but in my opinion, it invites investigation. Regards, EdB -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Thursday, September 14, 2000 12:08 PM To: [email protected] Subject: Near Field Versus Far Field I am having a difficult time answering the following question for a non-technical person. Hopefully, someone can put the answer into a language that a non-technical person can understand. We have a 400 MHz clock and are failing radiated emissions at 10 meters by 10 dB at 400 MHz. We bring the product back to our lab and start making modifications on the clock circuit and taking measurements with a near field probe. With these modifications and measuring with a near field probe, we realize a 10 dB reduction in emissions at 400 MHz. Why would we not see the same reduction when taking the product back to a 10 meter site? Your help is appreciated. Regards Joe Martin [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
