suitable substrate for antenna in 868MHz

hallo,

what material is suitable for the substrate of antenna in 868MHz?

How about FR4 of PCB?

thank you very much in advance!

One problem with FR4 is the variation in its dielectric constant from batch to batch. It can vary by at least +/- 0.5. Maybe your antenna design can take this variation. A quick simulation check using the extreme values for the dielectric constant will answer this. If this is acceptable then fine, use FR4. If you need a material with a better controlled dielectric constant at a reasonable price. I would use Rogers 4000 series.