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.

This paper presents the analysis and design of a high-efficiency broadband Class-EM power amplifier (PA). The inherent broadband characteristic of the Class-EM PA that turns out due to the resistive-reactive impedance terminations at the fundamental and second harmonic frequency is first investigated and then extended using double reactance compensation technique by incorporating a parallel resonator LPCPinto the main circuit's load network. Designed using GaN HEMTs, the PAs deliver 23.7% (without LPCP) and 60.4% (with LPCP) fractional bandwidth, within which the PAE is larger than 60% and the output power is relatively constant.

In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of power amplifiers. This paper-overview describes the historical aspect of the Doherty approach to the power-amplifier design introduced in 1936 and modern trends in Doherty amplifier (DA) design techniques using multistage and asymmetric multiway architectures. To increase efficiency over the power backoff range, the switchmode class-E, conventional class-F, or inverse class-F operation mode by controlling the second and third harmonics can be used in the load network. The DA with a series-connected load, and inverted, push–pull, balanced, and parallel Doherty architectures are also described and discussed. Finally, examples of the lumped DA implemented in monolithic microwave integrated circuits, digitally driven Doherty technique, and broadband capability of the two-stage DA are given.