FR4 as PCB substrate for circuits at above 1 GHz

NO!

That said, I have seen SIMPLE circuits operating on FR4 up to 4.2 GHz. Just don't try to do any filters! The big problem is that the thickness and dielectric constant are not very controlled. Also, the dielectric constant is changes in each axis.

Careful selection of fibre glass board vendor would actually make GHz design possible on FR-4 type substrates. You will have to specify resin content, fibre glass thickness and roughness, method of copper lamination and tolerances of the material's physical properties. But as biff44 writes: Don't even think of making any distributed filters. I have made several designs at 2.45 GHz (Bluetooth, WLAN), but the relative high losses will have to be accepted so designs must be kept small.

What is your guys prefer for GHz antenna substrate? How about RT5880?

The Teflon materials are quite difficult to handle for many board manufacturers. There are other "semi-ceramic" materials that performs well on GHz frequencies that can use the same processes as fibre glass board materials. I have had good experience with some from Rogers Corp.

Hi ckjj

look at https://www.edaboard.com/viewtopic.p...&highlight=fr4

and https://www.edaboard.com/viewtopic.p...&highlight=fr4

RGZ