Abstract: This paper proposes a miniaturized power amplifier at 3. 5 GHz based on the the hairpin microstrip bandpass filter. The cascade coupled microstrip line is “U” shaped to reduce the size of the output matching circuit, which can be directly matched to 50 Ω load without designing the fundamental matching network. The filter is based on the parameters of the third-order Chebyshev low-pass prototype filter and has high selective in band response and strong out of band suppression. The odd and even mode impedance analysis is used to calculate the filter parameters. The test results show that at 3.2-3.7 GHz, the saturated output power is up to 41.2 dBm, the saturated drain efficiency is 50.2% - 61%, and the gain is greater than 10 dB.