A High-Efficiency Outphasing Power Amplifier Utilizing a Synthesized Direct-Matching Technique Based on Two-Section Branch-Line Coupler Output Combiner

To efficiently amplify modulated signals with high peak-to-average power ratios (PAPRs) in 5G and future 6G wireless communication systems, outphasing power amplifiers (OPAs) are worth considering due to high efficiencies at back-off. To simplify the OPA design process, a new output power combining approach is proposed that utilizes a branch-line coupler without additional reactive compensation elements. Theoretical analysis provides a straightforward realization, of OPAs after synthesized direct-matching networks (SDMNs) are used to conjugately match sub-PAs with the combiner. The implemented OPA with measured peak output power of 39.7-39.8 dBm achieves drain efficiencies (DEs) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{6 1. 3 \% - 6 4. 1 \%}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 2 \% -}$</tex> 48% at saturation and at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6-\text{dB}$</tex> OBO from 3.4 to 3.5 GHz. Under excitation of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20-\text{MHz} 5 \mathrm{G}$</tex> NR signal with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8-\text{dB}$</tex> PAPR at 3.45 GHz, an average DE of 41% with an adjacent channel power ratio (ACPR) below <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{-45.2 dBc}$</tex> is obtained using digital predistortion (DPD).