Additive Phase Noise in Linear and High-Efficiency X-Band Power Amplifiers

This paper compares additive (residual) phase noise of linear and highly saturated high-efficiency MESFET and HBT 10GHz power amplifiers (PA). A custom discriminator measurement system is developed to characterize the PAs and exhibits a phase noise floor of -164 dBc/Hz at 10 kHz offset for a 10GHz fundamental. The additive phase noise measurements show a phase noise of -120dBc@1 kHz for the class-E MESFET PA, a roughly 10-dB increase when compared to the class-A PA with the same device. The HBT amplifier exhibited nearly the same phase noise in class E and linear class A.