1. A communication device, comprising: an antenna; a tunable impedance matching network coupled to the antenna; a memory to store instructions; and a processor coupled to the memory and the tunable impedance matching network, wherein responsive to executing the instructions, the processor performs operations comprising: determining at a terminal of the tunable impedance matching network an impedance mismatch caused by a change in impedance of the antenna; locating an impedance mismatch entry in a lookup table that approximates the impedance mismatch, wherein the lookup table comprises a plurality of complex reflection coefficients determined 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.