Generalized Active N-Port Network Analysis for Load Modulation: Doherty Power Amplifier Incorporating Tri-Coupled-Line Combiner

This work aims to explore novel ideas and architectures to implement flexible, high-efficiency load modulated amplifiers. A set of versatile closed-form equations, termed VIP equations, is derived for analyzing active N-port networks. These equations are applicable to a wide range of issues, including load modulation (LM) in amplifiers and mutual coupling in multiple-input and multiple-output (MIMO) systems. To illustrate the use of these equations, they are applied to several conventional LM structures such as Doherty amplifier and load-modulated balanced amplifier (LMBA), enabling broader design space exploration. To demonstrate how to invent new architectures using VIP equations, a novel load-modulated architecture, termed Tri-Coupled-Line Doherty Power Amplifier (TCL-DPA), featuring a six-port three-coupled-line combiner, is proposed and analyzed. This architecture offers significant advantages, including design flexibility, enhanced back-off efficiency, while maintaining simplicity in design and implementation. The output back-off equation of the TCL-DPA is equivalent to DPA, with efficiency characteristics close to three-way DPA and Sequential-LMBA (SLMBA), but without the overdrive challenges associated with SLMBA. The TCL-DPA prototype was designed and implemented as a proof of concept, delivering 45 dBm at 2.4 GHz with %58 efficiency at 9 dB output back-off (OBO) and -35 dBc ACLR under a 10-MHz modulated signal.