An embodiment of the present invention provides a RF power amplifier. The RF power amplifier comprises an RF input distribution network, multiple amplifiers and a signal combining network. The RF input distribution network is configured to divide an input RF signal into a main input signal and an auxiliary input signal. The multiple amplifiers are coupled in parallel to the RF input distribution network and configured to amplify the main and auxiliary input signals respectively by a main amplifier contributing a larger portion of the output power of the RF power amplifier and an auxiliary amplifier contributing a smaller portion of the output power of the RF amplifier. Each of the main and auxiliary amplifiers is selected from the amplifiers according to an impedance ZL of the transmit coil. A loading level of the main amplifier is modulated to alleviate loading mismatch condition of the main amplifier by adjusting current contributions from the main amplifier and the auxiliary amplifier according to the impe
