An analysis technique for a small pulsed source connected to a large sink with application to gallium arsenide IMPATT diodes

A methodology using numerical techniques is presented for the thermal analysis of a physically small pulsed heat source which is closely coupled to a relatively large heat sink. The methodology consists of creating a hierarchy of finite-difference models. These models consist of a highly detailed source model and several progressively less detailed sink models. The proper node size and time step for each model is individually determined depending on the geometry and pulse frequency. This process provides for efficient computer use by breaking the problem into several individual models with overlapping boundaries and the complexity of each model remains manageable. The methodology is applied to the analysis of a GaAs impact avalanche transit time (IMPATT) diode power combiner. This combiner is the radio-frequency source for the terminal guidance unit in a current air-to-air missile. The analytical predictions compared favorably with test results. The analysis was performed using the Hughes Aircraft Company proprietary version of the general thermal analyzer code CINDA