Transparent Protective Coating for x band Frequency

Hi
I make a patch Antenna for x band and I want to use a protective coating(Spray , ...) for it.
which material should i use?

My experience is that THINNER coatings are the best for microwaves. Something like this should not change the performance much:

http://www.productionsupplysolutions...shoppingengine

If you want cheap, any sort of lacquer varnish should do. The silcone coatings seem to end up thicker and pull the frequency around more.

Maybe two-layer board can be used in some cases. As dielectric thickness is known, calculations and simulations may be done. As a result - "invisible" inner-layer antenna. Altough it would be more expensive.

I've made the Antenna and now just want to coat it.