User terminals of modem mobile communication systems require efficient. low profile antennas, capable of broadband and multiband operation. In that respect. planar inverted-F antenna (PIFA) designs have emerged that explore the trade-off between the height above the ground-plane and the achievable effective bandwidth. Further possible bandwidth enhancements are studied, as is multi-band operation by switching and tuning the resonant frequency of the PIFA, while maintaining a low height above the ground plane.