Adaptive Input-Power Distribution in Doherty Power Amplifier using Modified Wilkinson Power Divider

This paper presents the formulation and experimental validation of adaptive input-power distribution in Doherty Power Amplifiers (DPAs) using modified Wilkinson Power Divider (WPD). It will be theoretically shown that ideal power-dependent power-distribution profile for Doherty operation can be obtained by just adjusting the isolation resistor in the divider when input reflection phase of the auxiliary amplifier in power-back off range are properly set. The proposed circuit was experimentally verified by fabricating a 3.5 GHz 32 W DPA using GaN HEMT devices. Experiments showed that, by optimizing the isolation resistor, ACLR improvement of 9 dB were obtained under 8.5 dB PAPR 10 MHz LTE signal. The optimized DPA based on this technique showed an average drain efficiency of 55 % and ACLR of −50 dBc using the same signal after Digital Pre-Distortion (DPD).