Add to ORKGThis paper presents the characterization of illuminated high-frequency active devices using a time domain physical simulation model. The model is based on Boltzmann's Transport Equation (BTE), which accurately accounts for carrier transport in microwave and millimeter wave devices with sub-micrometer gate lengths. Illumination effects are accommodated in the model to represent carrier density changes inside the illuminated device. The simulation results are compared to available experimental records for a typical MESFET for validation purposes. The calculated y-parameters of the device show the profound effect of illumination on the microwave characteristics. These findings make the model an important tool for the design of active devices u...