Automatic tunable antenna controlling varactors based on the received power of a probe

Built-in antennas in mobile equipments are often subject to changes in input impedance due to the proximity of objects, e.g. a user´s hand/head, a desk, etc. The resulting mismatch can lower the efficiency of the RF power amplifiers (PAs), will reduce battery life, cause low communications quality, etc. To mitigate these problems, a novel automatic tunable antenna system using a probe is proposed in this paper. The system controls two varactor diodes (VDs) in the matching circuit (MC) according to the received power of the probe. When the power is less than -20dB relative to the input power to the MC for all VD conditions, this corresponds to only -0.01dB loss which is considerably less than the insertion loss of a directional coupler. Moreover, the system is frequency independent, consequently significantly wideband, and can operate from 700MHz to 2.7GHz. A prototype using a programmable logic device (PLD) is also demonstrated.