The answer to this really depends on what you call high frequency
     (900 MHz or 30 GHz). Above 900 MHz one really needs to consider
     laminates designed for this purpose (low loss, controlled dielectric
     constant). Suppliers of these materials are Rogers, Taconics and
     Arlon. Speaking on Rogers (fax 602 961-4533 USA) behalf, the use of a
     material called RO4003 (woven glass saturated with hydrocarbon
     plastic/ceramic loaded) is recommended for commercial applications
     below 15 GHz. It has electrical properties for RF/microwave
     applications as well as being a material that can be fabricated like
     standard epoxy/glass material. If you want to discuss this more please
     let me know ([log in to unmask]).

     Regards
     Art Aguayo
     Technical Services Engineer
     Rogers Corp.