On 4 Oct 2006 17:44:57 -0700, "
wrote:


Roy Lewallen wrote:
K7ITM wrote:
Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.

But be sure to pay attention to UV susceptibility if your antenna is
exposed to the sun. Many plastics deteriorate quickly in sunlight, and
polypropylene is particularly bad. And of course you might need to
consider mechanical properties. Polystyrene is brittle and breaks quite
easily. Polyethylene and Teflon are soft, and Teflon cold flows. (I
don't know about polyethylene but suspect it might also.) Polycarbonate
is tough and nice stuff mechanically, but don't know about its UV
resistance.

Polycarbonate sheets in many sizes are found in do-it-
yourself stores as window glass replacement. While
expensive, most of those brands are marked "sunlight
resistant."

Lowes, Home Depot, OSH all carry polycarbonate "window
replacement" pieces here in southern California.

Those materials are apparently coated for UV protection. I put some
in the windows of a playhouse I built for my granddaughter and the
protective film was labeled as to which side should be out.