In this study, Class AB power amplifier was designed for use 3G and 4G mobile communication systems. Agilennt EEsof ADS(Advanced Design System) program was used for the design. BLF621-10G model transistor of NXP company was used as active element and Murata brand of coils and capacitors was used as passive elements. As a result of the design, a power amplifier design and simulation with 200 MHz bandwidth at 2.1 GHz was realized. When the designed power amplifier is exited with 17.5 dBm input power, a stable and good gain flatness(+/- 0.36dBm swing in the 20dB dynamic range) was obtained by obtaining 38 dBm oputput power.