Design of a tri-band single-loop load-modulated Doherty power amplifier

This article presents a novel tri-band Doherty power amplifier (DPA) architecture based on a single-loop L-C load modulation network. By introducing additional current and power combining nodes, this architecture enhances the degrees of freedom and design flexibility of the load modulation network, effectively mitigating the bandwidth limitations imposed by the λ /4 impedance transformer in conventional DPAs. Theoretical analysis demonstrates that the structure can regulate the current injection ratio at different frequency points through an L-C series resonant network, enabling multi-band impedance matching. Based on this architecture, nine sets of tri-band DPAs with different frequency ratios were designed, and an asymmetric DPA operating at 0.85–1.0/1.75–1.85/2.3–2.4 GHz with 8-9 dB output power back-off (OBO) was fabricated. Measurement results show a drain efficiency of 45.6%–57.5% at 8 dB OBO and a saturated output power of 43.3–46 dBm, verifying the feasibility and superiority of the proposed architecture for designing high-efficiency multi-band power amplifiers.