David Harper wrote:

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

In addition to the responses already posted, there is at least one other
possible, I repeat possible, requirement for pressurized waveguides,
antenna feedpoints, etc. It is to increase the breakdown voltage of the
local 'atmosphere' at very high power [e.g. megawatts at microwave
frequencies.]