If waveguide isn't pressurized with a dry gas and it has any pinholes it
will breath outside ambient as temperature cycles. Later the water vapor
will condense on the walls of the WG and as it collects it will flow to low
spots of the WG. You know the rest of the story. In non-operating systems
in freezing climates you'll see expanded (somtimes split) WG from water that
froze in the low spots.

--
73
Hank WD5JFR

"David Harper" wrote in message
om...
I'm working on a project that involves antennas that appear to be
pressurized with nitrogren (approx 10psi). What purpose does this
serve? Does it help with transmission properties, gain, etc? It is
used on an aircraft, if that is a factor.

Thanks in advance!
Dave