Design of a High Gain Linear Power Amplifier for 2.4 GHz ISM Band Applications

High gain linear power amplifiers are needed in modern industrial, scientific, and medical (ISM) systems to increase the transmission range and to produce distortion-free signals. The aim of this paper is to develop a design approach for a multi-stage linear power amplifier that can be used in the 2.4-2.5 GHz ISM band. The amplifier chain consists of three stages to raise the input power level from 0 dBm up to 39 dBm with an overall power gain of 39 dB. The first stage is designed using a medium power GaAs pHEMT transistor by means of the scattering parameters, while the second and third stages are synthesized based on a commercial GaN HEMT power device using the load/source pull technique. Microstrip lines have been used in the implementation of the matching networks to minimize the effects of parasitic elements and to reduce the power losses. The simulation results show an overall DC-to-RF efficiency of 55%, and 38 dBm output RF power at the 1-dB gain compression point (P_1dB) across the band of interest. The simulated second harmonic distortion is better than 38 dBc, and the adjacent channel power ratio (ACPR) is high enough at the desired center frequency. These results confirm that the proposed amplifier circuit provides high gain and acceptable efficiency in addition to improved linearity.