What causes reflected power at an antenna’s feed point?

Reflected power occurs when radio frequency (RF) energy traveling down a transmission line hits a boundary where the electrical characteristics change abruptly. In an antenna system, this boundary is the connection between the feed line and the antenna's feed point. For maximum power transfer to occur, the characteristic impedance of the feed line must perfectly match the feed point impedance of the antenna. When these two impedances are matched, all the forward energy is absorbed by the antenna and radiated into space. If there is a difference between these two impedances, a mismatch occurs. This impedance mismatch acts like an electrical barrier, preventing all the forward power from being absorbed. The unabsorbed energy has nowhere else to go, so it is reflected back down the feed line toward the transmitter.