High efficiency power amplifier for high frequency radio transmitters

Modern transmitters usually have to amplify and transmit complex communication signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B or AB) are usually employed as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents solutions for the power supply that acts as the envelope amplifier and class E amplifier that is used as a nonlinear amplifier. The envelope amplifier is implemented as a multilevel converter in series with a linear regulator and can provide up to 100 W of peak power and reproduce sine wave of 2 MHz, while the implemented class E amplifier operates at 120 MHz with an efficiency near to 90%. The envelope amplifier and class E amplifier have been integrated in order to implement the Kahn´s technique transmitter and series of experiments have been conducted in order to characterize the implemented transmitter.