[Antennas] Painting of Antenna Radomes

[Barry L. Ornitz]

Tom, WA2BPE, wrote:

> I would be careful of what paint is used as some may be good
absorbers
> at microwaves - you may wind up with something waterproof - and no
> signal!  No, I have no data to back up what will/won't work.  Also,
I am
> not sure, but this may hv been discussed some time back; perhaps an
> archive search is in order.  Perhaps check the microwave archives
too.

There are some very different considerations when painting
microwave antennas as I clearly stated earlier.

For painting a radome, where the signal must pass through the
coating, you need not only low loss, but a dielectric constant
similar to the existing radome material.  Since many radomes
are made of acrylic plastics for low losses, you also need to
make sure the paint is compatible here.  Many solvents will
either soften or dissolve these plastics, and while other
solvents may not, they can still cause stress corrosion
cracking of these plastics resulting in an extreme loss of
strength.  Painting a microwave reflector is an entirely
different issue.  High dielectric constant is of benefit here.

Titanium dioxide, the preferred white pigment of most paints
these days, has an exceptionally high dielectric constant.  In
fact, this material is commonly used in the ceramics of high-K
ceramic capacitors.  It works great in paint used on
reflectors like a parabolic dish.  But it is not suitable for
use in radome paints.  Lead oxide might be more suitable from
an electrical standpoint, but its toxicity keeps it from being
used in modern paints.

The painting of microwave antennas is a complex subject with
lots of trade-offs.  To read more about the materials, consult
the reference to Jasik and Johnson I gave earlier.

        73,  Barry     WA4VZQ     ornitz@tricon.net