Current density dominant mode on spiral patch antennas

An elegant and efficient way to calculate and analytically show the main features of spiral patch antennas is presented in the following. The derivation of an approximate analytical expression for the dominant current density mode on the patch is firstly presented, from which it can be easily calculated the patch radiation pattern. Its invariance with frequency scaling, which is the main feature of such log-periodic antennas, is in particular shown, together with a good agreement with experimental results. An extension to higher-order modes for a MoM analysis of the current density is then suggested, which may be useful to study with more accuracy the other antenna characteristics, such as gain and input impedance at the feed.