Polarisation-diversity antenna for TPMS application

A low profile antenna, with polarisation diversity, for operation in a tyre pressure monitoring system (TPMS), is investigated. By combining the signals received from the two ports in phase or 180deg out of phase, the antenna can operate at two different modes: a top-loaded monopole antenna and a planar dipole antenna located very close to a conducting plane (about 0.028 lambda). Two significant techniques are used to enhance impedance bandwidth and to reduce antenna length. A prototype is implemented and the results obtained are given.