This is a follow up on answer by Holger Fiedler here: https://physics.stackexchange.com/a/622802/230132
He writes that an antenna powered by alternative current (AC) will emit other frequencies than the AC one, citing x-ray emissions from Mhz radar sources.
What is the distribution of these "undesired" frequencies? Is it a mere bell centered on the AC frequency? Also, is it due to imperfections in the materials, quality of current, etc, or is it a phenomenon intrinsic to varying intensity sources?