Sensitivity of Microwave Power Transistors to Low Frequency Impedance Variations

Low frequency impedance variations have been identified as having an adverse effect on the linearity performance of microwave power transistors. The presentation of frequency independent and broadband low frequency impedances across the wide modulation bandwidth is of paramount significance for robust characterization of microwave power transistors for future wireless communication systems. This paper presents a refined active loadpull measurement system to allow the precise independent control of all the significant low frequency components generated as a result of complex modulated excitation. The investigations are carried out on a 10W pHEMT microwave power transistor when driven to deliver a peak envelope power of approximately 39.7dBm under 9-tone complex modulated stimulus.