how select substrate?

hi,all
thanks for reply my ask. i visit the McMaster site for polyethylene, but i couldn't find relative permitivity (er=?) of material.
is there er=10.2 ?
and what is reason for select slab plastic? is there "er" for this?
i embeded bar metal (like stub short circuit) in coxial cable, perpendicular on inner conductor. whether could embeded bar in this substrate?

er of polyethylene is 2.25 Relative permittivity - Wikipedia, the free encyclopedia

Keith.

---------- Post added at 09:47 ---------- Previous post was at 09:45 ----------

As you have already asked this question elsewhere I will close this thread. In future don't ask the same question multiple times.

Keith.