Characteristic mode analysis of a shorted microstrip patch antenna

The shorted microstrip patch antenna (or Planar Inverted-F Antenna - PIFA) is extremely effective at achieving significant miniaturization over the conventional microstrip patch antenna. In this paper, we perform an analysis on the shorted microstrip patch antenna and in so doing, provide insight into its true mode of operation. Using characteristic mode theory, we show that the insertion of the shorting component dramatically alters the antenna operation such that the fundamental characteristic mode no longer represents a patch-like but rather a monopole-like mode.