Electro-Thermal modelling of very High power Microwave bipolar Junction transistors

This paper describes a new approach to accurately characterise very high power, Si BJT, devices capable of delivering powers in excess of 250W, at L band, in a class C amplifier configuration. Conventional modelling approaches are not suitable for large power structures. An alternative electro-thermal, equivalent circuit model, has been constructed using a novel hierarchical approach. The thermal dependence of the device characterisation is removed during the extraction of the electrical circuit and is reinserted, within the model, using a suitably complex thermal network, determined using a fully physical thermal simulator. Theoretical and experimental results are shown for steady state and pulsed amplifier operation