A Nonlinear Drain Resistance Model for a High Power Millimeter-wave PHEMT

A millimeter wave high power PHEMT model with a nonlinear drain resistance Rd is proposed. The nonlinear Rd arises from electron velocity saturation in the gate-drain gap. At 2.1 GHz, the nonlinear Rd behaves like a conventional linear resistor. However, at Ka band, the nonlinearity of the resistance results in a large power loss. This frequency dependent phenomenon has been experimentally verified in millimeter-wave GaAs PHEMTs. Our proposed simple model accurately describes the power characteristics of these devices at 2.1 GHz and in Ka band