In this paper, a design methodology for realization of hybrid microwave power amplifiers (PAs) using discrete GaN HEMTs is systematically explained. High power solid-state amplifiers usually suffer from self-heating, high frequency instability, unbalanced feeding effects and suchlike that should be carefully taken into account in a reliable and robust design. Though most of these issues are discussed in some of the previously published literatures, a single self-contained document that systematically describes the hybrid microwave PA design is limited. In this work, a comprehensive design methodology for implementation of high frequency PA is presented while the important challenges of high power amplifier design are discussed in more detail and several useful practical hints are given. Especially, we focus on hybrid PAs that are realized using large gate periphery GaN HEMTs. As a real example, a PA is fabricated using a 0.25  μm GaN on SiC HEMT transistor with a gate width of 12.5 mm. The fabricated PA achieves a 12 dB small-signal gain, 30 W output power, and 52% PAE across the frequency range of 9–9.8 GHz. The thermal analyses of the power transistor are performed using a 3D model, which is developed in ANSYS software and calibrated by measured data. The model can be used to calculate the transistor channel temperature and consequently predict the device lifetime.

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