What is different from a common mode current and a standing wave current on an unbalanced transmission line.



There is confusion in the mind of beginners and even with some more experienced individuals, common mode currents and VSWR are often confused, they are not the same or related to each other.
Le me give you an example, one can have an antenna with a perfect VSWR yet get lots of RF back into the shack, why is this?
The simple answer is that common mode currents are caused by imbalances in the matching (Balanced to Imbalanced) system, that these curents flow on the outside of the shield.
An impedance mismatch (VSWR) return currents flow on the inside of the shield.
The kind of matching used for balanced to imbalanced (BALUN) is very important to minimize the common mode currents, if the matching was ideal, then zero common mode current will result, in reality this is not possible, there will always be some common mode currents that can be reduced with careful design of the matching system.
The best solution is to use a balanced transmission line, this avoids common mode current provided that the antenna is a perfect balanced load, further that the balanced transmission line is not effected by things like gutters, walls etc.


Link to article for further insight.