When you bring an antenna close to a conductor, say a dipole next to a plate, the radiation resistance decreases. This is due to the currents induced in the pl

When you bring an antenna close to a conductor, say a dipole next to a plate, the radiation resistance decreases. This is due to the currents induced in the plate, creating an image and reinforcing the currents in the dipole. It’s really the ratio of radiation resistance to conductor resistance. You can shrink an antenna to infinitesimal size, made of perfect conductor, but as the radiation resistance decreases, it’s more difficult to impedance match. An infinitesimal antenna would have zero bandwidth. Sort of like Bode Fano criteria limiting bandwidth versus impedance. There is a Chu theoretical limit which limits antenna efficiency and bandwidth given volume, hence 3D fractals and other stuff. Ain’t no free lunch. A lot of antenna research is who can get closest to the Chu limit. Sort of like coding and the Shannon capacity. https://en.m.wikipedia.org/wiki/Chu–Harrington_limit https://en.m.wikipedia.org/wiki/Chu–Harrington_limit There is still a lot of snake-oil in antennas, some of it fractal related.