I am sure a write-up is here somewhere, but I cannot find it. Lets say I wanted to measure VSWR parameter of some arbitrary freq range. I can analyze just the antenna, or I can attach the antenna to a Tx with transmission line. If I analyze just the antenna, will that VSWR look the same as connected to the Tx? Perhaps in other words, does Tx output stage affect overall "system" VSWR? I assume it would. So, if Tx is a variable in the VSWR equation, then why do we analyze just the antenna?