A New Approach to Design a Broadband Doherty Power Amplifier via Dual-Transformation Real Frequency Technique

A novel dual-transformation simplified real frequency technique is proposed in this paper to synthesize a broadband Doherty power amplifier (DPA). The proposed method can realize the co-design of the carrier and peaking output matching networks to achieve dual-impedance transformation at back-off (BO) and saturation simultaneously. To realize this method, a generalized driving point function with different loads of the matching network is proposed, and weight factors are adopted to combine the separate target functions to form a united one. Compared with conventional designs, no initial guess is required and additional compensating lines are eliminated to improve the performance of the DPA. Based on the proposed technique, a broadband DPA is designed and fabricated across 2.2-3.7 GHz (51% fractional bandwidth). The measurement results show that the designed DPA has a 6-dB BO efficiency of 45%-53% and a saturated output power of 43-44.6 dBm over 1.5 GHz bandwidth. Various modulated signals including 80-MHz long-term evolution-advanced signal and concurrent dual-band signal are employed to validate the DPA. In this way, the DPA can achieve an average efficiency of 45.3%-55.9% at 6.5-dB BO with the adjacent channel leakage ratio levels better than -48.6 dBc by utilizing digital predistortion.