Broadband Doherty Power Amplifier Design Using an Extended Two-Port S -Parameter Solution Set With Irregular Matching Networks

This article presents a comprehensive design methodology for broadband Doherty power amplifiers (DPAs) based on an extended two-port <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula>-parameter solution set and irregular matching networks. Instead of designing the carrier, peaking, and post-matching networks separately, the entire output combining network (OCN) is modeled as a single two-port network, which captures the real interaction and load modulation mechanisms that determine wideband Doherty performance. To enlarge the feasible design space, the optimal load impedances obtained from load-pull simulations are processed using polygonal Boolean operations to extract their common high-efficiency, high-power region, followed by Poisson-disk sampling to generate a diverse set of impedance candidates. These impedances are converted into a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula>-parameter solution set, any of which is acceptable for proper Doherty load modulation. An irregular microstrip matching structure is introduced to provide additional degrees of freedom and enable direct layout-level optimization. A two-stage selection and joint optimization is then developed, where passive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula>-parameter matching and active large-signal performance are jointly used to guide the design. To validate the proposed approach, a 1.2–3.1GHz DPA with an 88.4% fractional bandwidth is designed and fabricated. Measurements show saturated output power above 43.1dBm, saturated efficiency of 51.8%–70.6%, and 6-dB back-off efficiency of 50.3%–55.6%. With digital predistortion (DPD), the adjacent channel leakage ratio (ACLR) is better than −50 dBc.