Abstract: The traditional single parallel analog pre-distortion circuit has low adjustability and it is limited to improve the third-order intermodulation (IMD3) of the power amplifier. In order to solve the above problems, this paper presents an S-band analog predistortion circuit,which can effectively compensate the phase distortion using the open stub. The analog predistortion circuit can adjust the phase difference between the fundamental signal and the IMD3 signal generated by the Schottky diode. Consequently, the characteristics of the analog predistortion circuit are opposite to that of the power amplifier, thus the IMD3 signal of the power amplifier can be reduced. Experimental results show that using the analog predistortion circuit, the IMD3 has been reduced over 34 dB at the 1dB of the 3.5 GHz class AB power amplifier.