Design Guidelines Using Characteristic Mode Theory for Improving the Bandwidth of PIFAs

It is well known that the bandwidth for a planar inverted-F antenna (PIFA) changes as the ground plane size changes. To gain insight into what causes bandwidth fluctuations, a process for applying characteristic mode theory to the finite ground plane and feed structure was developed. Four different PIFA designs are then evaluated to show how the modal significance of certain modes on the finite ground plane relate to the bandwidth minima and maxima for each PIFA. Next, finite ground planes are altered using the gained insight to enlarge the bandwidth for an antenna with a fixed maximum ground plane size. The goal of this work is to use the developed bandwidth analysis technique to inform the synthesis of PIFAs that require broader bandwidths.