Impedance changes. For the same amount of EM energy flow, as the transmission path impedance changes, the ratio of electric and magnetic fields change. The antenna characteristic impedance is important to the distribution from the transmission line
https://www.antenna-theory.com/basics/impedance.php
https://resources.system-analysis.cadence.com/blog/msa2022-how-to-measure-antenna-impedance
https://www.antenna-theory.com/basics/impedance.php
https://resources.system-analysis.cadence.com/blog/msa2022-how-to-measure-antenna-impedance