Dan wrote:
"Simply create a model of a coax feed to a poorly tuned dipole."

Dan has something there. The "ARRL Antenna Book" has an explanation of
"Commonn-Mode Transmission Line Currents" on page 26-16 in my 19th
edition. Launch of coax radiation is shown in Fig 24 on the same page.
This picture may be worth 1000 words.

Best regards, Richard Harrison, KB5WZI