Szczepan Bialek wrote:

The antenna always has the counterpoise:

Where is the counterpoise for these antennna:

A full wave loop antenna

A slot antenna

A horn antenna

For the purposes of the discussion, each antenna is driven by a small,
modular oscillator that has no chassis or metalwork of any kind and is
located half way between the Milky Way and the Andromeda Galaxy, i.e. it
is about 1,250,000 million light years from anything.