Luneberg lenses?

[Robert Stratton]

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.