[An antenna must have] current flowing along its length, so that the resulting fields radiate that energy into space. (Receiving antennas are just this process in reverse).
[This] explains why you can't just stick a small tank circuit on a board and expect it to radiate efficiently.
I understand this is true from experience, but I don't understand why. I guess the dimension of the antenna changes the fields it produces somehow, but how does this make energy radiate away more effectively? What's an energy radiating away look like?
I do understand the need to tune the antenna. I'm just wondering how after we've tuned for maximal power transfer to the antenna, we get more of that energy to go to the receiving antenna.