Bandpass Filtering Doherty Power Amplifier With Enhanced Efficiency and Wideband Harmonic Suppression

There is an ever increasing demand for both function integration and improved performance in wireless communication devices. Therefore, the integration of efficient linearizing amplifying and bandpass filtering functions is proposed for the first time in this paper. A new Doherty amplifier configuration with attractive behaviors including bandpass filtering, wideband harmonic suppression, and enhanced efficiency, is presented. A component crucial to the successful implementation of the proposed configuration is the bandpass quadrature coupler with arbitrary coupling coefficient. Owing to the flexibility of a circular patch in locating the frequencies of different operational modes, it is thus possible to implement good bandpass characteristics. With the introduction of this new component, the Main and Auxiliary amplifiers can be driven more efficiently, resulting in both linearity and efficiency improvements. To verify the validity of the proposed configuration, a Doherty amplifier has been designed and fabricated. Its measured performance is compared with the conventional design and found to exhibit a bandpass filtering characteristics with a wide suppression band up to the third harmonic frequency. Meanwhile, the proposed amplifier achieves a measured power-added-efficiency improvement of 10% and an ACLR improvement better than 5.8 dB at the higher output power region.