The Lower Bounds on Q for Lossy Electric and Magnetic Dipole Antennas

In this letter, the lower bound on Q is considered for a lossy electric and magnetic dipole antenna formed by a straight wire and a circular wire loop, respectively. Simple expressions for the lower bound on Q are written directly in terms of the dipole antenna's electrical size and loss resistance and are compared with numerical simulations. It is shown that the lower bound on Q for the lossy straight-wire electric dipole increases without bound with decreasing frequency, whereas the lower bound on Q for the lossy circular-loop magnetic dipole approaches zero with decreasing frequency.