Global Design of a Waveguide X-Band Power Amplifier

The design and the fully coupled Thermodynamic and Structural Mechanics simulation of a Spatial Power Amplifier are described in this paper. The amplifier is realized in a WR90 waveguide, employing Fin-Line Transitions and Monolithic Microwave Integrated Circuit Solid State Power Amplifiers. Global performances of active devices and combining structure have a critical dependence to the thermo-mechanical condition of operation. The temperature alterations and thermal expansions, related to the power dissipation of the devices, have been analyzed in order to lead the amplifier at extreme power output, avoiding malfunctions. The proposed analysis accounts for the effects of different distributions of heat flux and stresses as a consequence of the different power consumption of the Driver and Final stage transistors. The amplifier combines 16 active devices of 7.9 W maximum power output with a power dissipation of 20 W, heating the transistor channel to140° and deforming the mechanical structure to 4.9µm with a maximum stress of 0.41 GN/m2. A maximum power output of 112W with a Return Loss greater than 12 dB in the whole X-Band is ensured