A tuning method for the post-processing optimization of the Doherty power amplifier frequency band

The discrepancy between models and actual components sometimes causes the shift of the operating band of the realized circuit. This side effect is not acceptable and difficult to predict in many applications. This paper proposes a post-processing method to tune the frequency band of a hybrid Doherty power amplifier (DPA) after its implementation. The solution is oriented to the DPA based on a branch-line coupler as output combiner, which ideally requires an open circuit termination at the fourth port. This termination can be used to optimize the operating band of the module. The proposed approach is verified through a hybrid DPA based on commercial GaN devices. The results demonstrate the possibility of tuning the operating band of about 100 MHz (from 1.95-2.25 GHz to 1.85 -2.15 GHz) with negligible effects on the output power, gain, efficiency and bandwidth.