Electrothermal modeling and measurement for spatial power combining at millimeter wavelengths

In this paper, the first completely physical coupled electrothermal model, suitable for large-signal simulation of MESFET- and HEMT-based MMIC's and MMIC arrays, on a timescale suitable for computer-aided design, is presented. The model is validated experimentally by high-resolution thermal imaging of a MMIC 38-GHz three-stage balanced amplifier, mounted on a Cu/FR-4 substrate and cooled entirely by natural convection and radiation into free space.