On Fri, 29 Apr 2016 07:14:05 +0000, "Pawson, James" <james.paw...@echostar.com> wrote:
> 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? In a perfect anechoic chamber with no reflection, under far-field conditions, we expect to see inverse square law. Actually, absorber walls will have some reflections, which can affect to signal propagation in the chamber. Typically, we may see some ripple in the attenuation curve. In case of semi-anechoic chamber which mimic open area test site on the ground, signal propagation is significantly affected by floor reflection. > 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? I think not only absorption but wave cancellation and scattering also contributes to return loss. > 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. I don't think so. Foam absorber may reflect some of the incident wave, which can no longer absorbed by backing ferrite tile. > 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? I think it depends to the absorber. Regards, Tom - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
