Broadband GaN MMIC Doherty Power Amplifier Using Compact Short-Circuited Coupler

In this letter, a broadband gallium nitride (GaN) monolithic microwave integrated circuit Doherty power amplifier (DPA) using a compact short-circuited coupler (CSC) is presented. To enhance the bandwidth and reduce the size of integrated DPA, the conventional $\lambda $ /2 transmission line in the peaking output matching network is replaced by the CSC structure. Detailed theoretical analysis and design procedures are provided. Based on the proposed solution, a 5.1–7.2-GHz DPA is designed using a 0.12- $\mu $ m GaN HEMT process. The fractional bandwidth (FBW) is 34.1%. The measurement results show a saturated output power of 37.2–39 dBm and a 6-dB back-off drain efficiency of 38.4%–50.5% across the design bands with a chip size of $2.6\times 2$ .6 mm. The adjacent channel power ratio (ACPR) under 100-MHz single-carrier 64 QAM modulation signal with a 6-dB peak-to-average power ratio (PAPR) excitation is better than −45 dBc with digital predistortion (DPD).