I have not come across the terms "voltage loop" and "current loop" before so doing some research.
Google for one is useless, nothing seems to fit antennas or transmission lines, and if I add "feedline" or "antenna" to the search it refers to loop antennas only...
I did note that there are index entries in the 15'th and 16'th editions of the ARRL antenna books. These entries did not exist in the 14'th edition, and were gone by the 18'th edition. (I don't have a 17'th edition... yet...) When I looked at the same chapter in the 18'th edition, which has the same name, that whole section has apparently been rewritten and shortened.
When I read that section in the two books that have it they are referring to voltage and current loops in the antenna itself, not the feedline. I think this forum typically uses the term "node" in place of "loop", however, "peak" would also do nicely.
I am curious as to how you are applying this to a feedline as in a feedline the forward voltage and current are in phase with each other, and the nodes or peaks (or loops as you called them) are not stationary. When working with the reflected waveform, they are 180 degrees out of phase, which means the voltage and current peaks, while opposite polarities, still happen at the same points in the waveform.
Or am I completely misunderstanding what you are referring to by "voltage loop" and "current loop"?
Sorry for the hijack Leland...
The DB