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Message: <blockquote data-quote="spiney" data-source="post: 230536" data-attributes="member: 192438">Ho hum, sorry, I'm probably not explaining too well here (Spiney kills off previously interesting thread   .........   ok, so what's new?).For each hole in a metallic mesh (including sat dish), if the aperture (hole diameter) is significantly less than the electromagnetic wavelength going through it, then the other side of the hole you get an Airy disc pattern, so there's as many discs as there are holes. The pattern intensity corresponds to the Frauenhoffer I value as given by Wiki (the Java interactive demo doesn't show this intensity variation, since that's really about photographic lenses and photography!).So, yes, there's some energy gets through the holes, but only a tiny amount!It gets different if you start to deliberately EXTRACT energy from this tiny field, since then you've created a "conduit". In waveguuides, there's a tiny slot in the waveguide wall - much smaller than a wavelength - but a "probe" going through this tiny slot can extract nearly all the energy (and that's exactly how lnbs work!).( <a href="http://www.fnrf.science.cmu.ac.th/theory/waveguide/Waveguide%20theory%209.html" target="_blank">www.fnrf.science.cmu.ac.th/theory/waveguide/Waveguide theory 9.html</a> <a href="http://www.tpub.com/content/et/14092/css/14092_75.htm" target="_blank">www.tpub.com/content/et/14092/css/14092_75.htm</a><a href="http://www.tpub.com/content/et/14092/css/14092_74.htm" target="_blank">www.tpub.com/content/et/14092/css/14092_74.htm</a> ).It gets different again, if you start making the aperture LARGER than the wavelength, as then you've made an "aperture antenna" (common for terrestrial tv, and newer type plate arrays of these are used on some Freeview transmitters).( <a href="http://www.ee.surrey.ac.uk/Personal/D.Jefferies/aperture.html" target="_blank">www.ee.surrey.ac.uk/Personal/D.Jefferies/aperture.html</a> ).( <a href="http://www.grc.nasa.gov/WWW/RT1999/6000/6150zakrajsek.html" target="_blank">www.grc.nasa.gov/WWW/RT1999/6000/6150zakrajsek.html</a> ).Which takes us back to the BSB squarial, see retro-tech section above ...(added) the physics of fourier optics is the same - at much smaller wavelengths - as radio waves going through appropriately larger apertures (ignoring energy coupling, which admittedly is different, due to the relative size of atoms!). Strangely, the radio wave version is usually presented in mathematical equations, but the optical version in pictures. Maybe because of the photography connection? Anyhow, although both versions are alternative presentations of exactly the same thing, of course we find it much easier to "understand the pictures"!eg, both maths and (some very pretty!) pictures at: <a href="http://www.opticalimaging.org/fourieroptics.html" target="_blank">www.opticalimaging.org/fourieroptics.html</a>Never ever let the maths put you off ........  !</blockquote>

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