Variable Antenna Load for Transmitter Efficiency Improvement

A wireless radio transmitter with an integrated variable-impedance antenna is demonstrated. The transmit signal is connected via a switch to the antenna at one of several feed points that correspond to different load impedances that are optimal for the power amplifier at different transmit power levels. It is shown that this can be used to improve the efficiency of the transmission at low and medium transmit powers. The variable antenna load is demonstrated with a planar inverted-F antenna, but the method can be applied to any antenna with suitable impedances.