David G. Nagel wrote:

What I was taught is that in a properly installed antenna system the
coax will not radiate. If the antenna is not properly matched to the
coax you get current flow along the outside of the coax shield.

Dave WD9BDZ

It's too bad people are being taught this. As a number of others have
correctly said, impedance match has nothing to do with whether or not a
coax (or symmetrical twinlead line) radiates. Radiation is due to other,
unrelated causes.

Roy Lewallen, W7EL