A monopole antenna constitutes half of a dipole antenna. Monopole antennas use a ground plane, normally a designated space on the PCB, as the other half. This ground plane allows a smaller antenna to radiate RF energy more efficiently. To maintain good performance, the ground plane should not extend under the antenna chip itself.
A planar interverted-F antenna (PIFA) has a rectangular planar element located above and parralel to a ground plane. PIFA antennasmay be mounted on top of a ground plane. PIFAs resemble regular inverted-F antennas, which are a type of monopole – these radiate energy from the top of the antenna.
PIFA antennas have the advantage of being resonant at a quarter wavelength, which means they require less space on a circuit board. Furthermore, they have good SAR properties. Due to these properties, it is being used increasingly in miniaturised devices.