mo at ccr.org
Wed Oct 25 23:07:13 CDT 2006
Robert Stratton wrote:
> Has anyone here built their own Luneberg lens? The current issue of
> Tele-Satellite magazine has an interesting article on them, and an article
> on a multifeed helmet antenna used for omnidirectional reception of DVB-S
> television signals.
> It's hardly a bastion of fashion sense, but the builder, Dr. Farrag (an
> Egyptian M.D.) even integrated a small DVB receiver into the helmet. He uses
> two LNBFs and has received programming from NILESAT, ARABSAT and HELLASAT
> from Cairo.
> The thing I'm wondering is how people have laid up the "mille fois"-like
> laminations of various layers to achieve the smoothly varying dielectric
> constant necessary to make one of these things work? Is it really as simple
> as layering concentric circles of material in ever smaller diameters?
> The equation for varying the dielectric constant seems straightforward
> enough. I'm wondering how practically difficult it is to achieve this with
> commonly-available materials?
> --Bob S.
not long ago, i was talking to a communications satellite design guru
and after finishing out primary conversation topics, i asked about
"What ever happened to the great promise of the Lunenberg Lens?"
he chuckled and said, "People discovered it's a lot harder to do than it looks."
it seems that Lunenberg Lenses are notoriously difficult to build and even tiny
variations in the structure produce huge performance deltas. There have been a
couple of large satellite projects which started with the intention of using
Lunenberg Lenses for terminals, but the manufacturing difficulties scuttled those
attempts. if you are incredibly careful and insanely patient, you can possibly build
one that will work reasonably well. building them in commercial quantities
with realistic cost targets has proven elusive, even given willingness to
invest in very expensive up-front tooling. QC on materials and fabrication
details ends up eating you alive.
but it sounds like a great project for long, cold 6-month winter nights. (grin)
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