Linearity of X-band class-F power amplifiers in high-efficiency transmitters

Modern communication signals have time-varying envelopes with significant p eak-to-average ratios, resulting in low average efficiency when amplified b y commonly used linear power amplifiers (PAs), For linear amplification wit h increased average efficiency, the Kahn envelope-elimination-and-restorati on method uses a highly efficient saturated PA. In this paper, an 8.4-GHz c lass-F PA with 55% maximum instantaneous efficiency at 610-mW output power, is experimentally characterized in several different biasing modes. Operat ed in linear mode with constant drain bias, this PA has 10% average efficie ncy, The suppression of two-tone intermodulation products is 27 dBc when op erated at about 0.7 times the peak output power. For the same PA operated i n a modified Kahn mode with drive and bias control, a comparable linearity (27.7 dBc) can be obtained at peak output power. Furthermore, the average e fficiency increased to 44%, a factor of 4.4 over the linear fixed bias mode .