Here is microwave printed circuit board material 25 mil (.025 inch) thickness, backed with a 1/16 inch thick copper plate for heatsinking! This is made by Rogers Corp, Duroid brand, dielectric is type 6010, has 1/2 oz electro-deposited (the low loss stuff) copper on top, 1/16 inch copper on back side. Dielectric constant is 10.8 so a 50 ohm line is about 25 mils across. The sheets are 10x10 inches + cut from larger sheets with a bandsaw. I chose this size as it is easy to ship. Heavy due to the copper backing, but worth it as you can mount power transistors and get some heatsinking as well as good grounding  This is the stuff for microwave and millimeter wave PCB's.  Easily etched and cut for various uses. You are buying 1 piece at a time.

Please see my list for other microwave goodies, and if you do not see it, ask!  I combine items to save you on shipping!