On Tue, 14 Sep 2004 11:31:29 -0700, "Andrey"
wrote:

PVC is not lossless, however...

I used PVC drainage pipe (white, 3 mm thick maybe) to make radome for 900MHz
antenna. Specifically, directional patch arrays. It tuned them down a little
bit (2 mm maybe over half-wave length.) I did not measure significant
decrease of gain. The cover did not touch the radiator. When it touches,
loading get significantly worse.

tnx for your reply

But it seems to me that what you describe is not so much that the PVC
absorbs energy ("loss") but instead: that it unavoidably de-tunes the
antenna because of its high dielectric constant (about 5 to 9 I
understand). Especially when the PVC touches the radiators the
capacitance between radiator parts is markedly reduced because of this
phenomenon (anyway that is how I intuitively understand it...)

Alex