Many thanks to all who replied on the subject. I have made some measurements in our chamber using a broadband noise source at different positions relative to the receive antenna. The aim was to characterise the chamber performance and check for any reflections or non-ideal performance. There is a summary of my results here:
https://drive.google.com/open?id=0B8tV5DDyzNucQW9uLThYLVF6MXM My conclusion is, at certain frequencies (e.g. 600MHz on last slide), there is an unacceptable amount of reflection in our chamber that appears to be partly caused by lower absorption from the ceiling and EUT wall. Any criticisms of the work or methods used or thoughts on what else I could try to establish if this is the case would be most welcomed. Many thanks James _____________________________________________ From: Pawson, James Sent: 29 April 2016 08:14 To: [email protected] Subject: Anechoic Chamber Questions Hello all, I have some questions about anechoic chambers that I need some help with and I'm sure there is some expertise in this group that can help. 1) My understanding is that an anechoic chamber is meant to simulate a reflection-less, free space environment. Therefore if you move a source towards / away from the antenna, the signal level should follow the inverse square law - correct? 2) When comparing absorber types (hybrid + ferrite tile vs. foam absorber) the return loss characteristic gives the amount of absorption at a particular frequency - correct? 3) If I wanted to compare effectiveness of foam absorber with hybrid + tile absorber is it just a case of adding the return loss of the hybrid to the return loss of the tile to achieve a final figure? My understanding is that the hybrid helps match the wave impedance from free space to that of the tile. Is the return loss of hybrid + tiles _together_ greater than the individual return losses of the separate components? Manufacturers that I've looked at list the data separately. 4) I have been told that the distance between absorber and a reflective metal backing is important for ensuring that the returning wave is in anti-phase (or at least as much as possible) with the incoming signal. However information on acceptable limits for this distance seems sporadic or in rarefied scientific papers behind paywalls. Does anyone have any info or experience on this point? Many thanks for your time, I'm trying to get a handle on our chamber's performance and any answers will help. Regards, James - ---------------------------------------------------------------- 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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
