@rarely if you are /that/ close to the antenna an extra tower, or any large amount of metal making the station more directional will definitely be unwanted, both by tradio station engineers and the Communications Ministry (licenses often require a particular directional pattern). But this is more an issue with LF and MF where waves are larger. At UHF/SHF frequencies for wifi harvesting could work but at present the component count required makes it less viable than other power sources.