Maximum Gain of a Lossy Antenna

An upper bound on the achievable gain of a lossy antenna is derived. This limit depends on the antenna size and a newly defined “loss merit factor,” which is shown to be a measure of the antenna material loss. The derived limit extends the well-known upper limit on the ratio of antenna directivity to its quality factor to the lossy antennas. Optimal antenna current distribution for the maximum gain is found, and the radiation pattern and antenna efficiency are also presented.