Radiating and balanced mode analysis of PIFA antennas

This paper presents a radiating and balanced mode analysis of planar inverted F antennas (PIFAs) mounted on wavelength-scale printed circuit boards (PCBs). The radiating mode shows, in a direct way, the extent to which the PCB influences both radiation and bandwidth. The balanced mode shows that the shorting pin acts as an impedance transformer in combination with a parallel reactance. Importantly, it can also be used to show that slots in the PIFA top plate nominally provide series reactance when the slot opening is close to the feed. Understanding of this behavior allows bandwidth improvements to be realized. It also allows dual-band antennas to be designed in a straightforward manner.