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.

Roy Lewallen, W7EL
I can speak to polycarbonate in a very small way: PCB ophthalmic lenses
are treated to provide excellent UV protection. But my understanding is
that pure PCB is not particularly UV resistant. Without a coating
(which provides the UV protection) it scratches very easily, so in that
sense, it is a soft material.

John
AB8O