1. A communication device, comprising: a power amplifier; an antenna coupled with the power amplifier; a tunable impedance matching network coupled between the power amplifier and the antenna, where the tunable impedance matching network includes one or more tunable reactive elements; a detector coupled between the tunable impedance matching network and the power amplifer; a memory that stores instructions and a look-up table; and a processor coupled to the memory, the detector and the tunable impedance matching network, wherein responsive to executing the instructions, the processor performs operations comprising: determining forward and reverse power at a terminal of the tunable impedance matching network via the detector; determining, at the terminal based on the forward and reverse power, an impedance mismatch caused by a change in impedance of the antenna; locating an impedance mismatch entry in the lookup table that approximates the impedance mismatch, wherein the lookup table comprises a plurality of complex reflection coefficients predetermined by measuring a signal at the terminal of the tunable impedance matching network for a plurality of impedance loads of the antenna; and using one or more complex reflection coefficients in the lookup table which correspond to the located impedance mismatch entry to tune the tunable impedance matching network.