The Doherty power amplifier (Doherty PA) is a popular back-off efficiency enhancement architecture proposed in 1936 for vacuum tubes and later adapted to solid-state transistor technology. Across the years the Doherty PA has evolved into various configurations which include asymmetric and multiway topologies to meet the stringent linearity and efficiency requirements of modern communication standards. Recent research efforts are focused on extending the Doherty concept toward millimeter-wave frequencies and monolithic integration. In this framework critical design trade-offs emerge: the gain penalty intrinsic to the Doherty architecture, often overlooked in favor of efficiency metrics, may become particularly severe and also impact the overall achievable efficiency. Bandwidth further constrains design choices, often forcing trade-offs between peak performance and wideband behavior. This also reduces the available design space to optimize linearity together with efficiency, which ultimately determines whether Doherty PAs provide sufficient advantages to justify deployment in place of non load-modulated class-AB PAs, generally more wideband, robust to process variations and simpler in terms of bias and architecture design.

The 10th IEEE International RF and Microwave Conference (RFM 2025), held from 17 to 18 September 2025 at the Bahang Bay Hotel, Penang, Malaysia, marked a milestone anniversary for the region’s RF and microwave community. Among the event’s many highlights were the Women in Microwaves (WiM) Forum, which carried the inspiring theme “Breaking Barriers, Building Futures: Women in Microwaves.”

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This article presents simple methodologies, fully compatible with commercial harmonic-balance (HB) simulators, to deal with the nonlinear behavior found in wireless power-transfer circuits, oscillator-based sensors, subharmonic injection-locked oscillators, and nonreciprocal isolators. The proposed methods allow the calculation of all the coexistent periodic solutions, including disconnected branches and closed loops that are not detected with conventional time-domain simulations or with standard HB continuation. Two main procedures are used, depending on how the circuit operates. For circuits driven at the fundamental frequency, we make use of a Norton/Thevenin equivalent and define a driven control function obtained from a single HB simulation. Constant-magnitude contours of this function give all disconnected solution curves versus the selected parameter and show how they evolve with input power. When the circuit is driven at a frequency different from the oscillation frequency, or a Norton/Thevenin description is not convenient, we define an equilibrium control function instead. In this case, all coexisting solutions are obtained by finding the roots of an equilibrium equation through a straightforward contour-intersection procedure. We also introduce hybrid methods in which the oscillator core is replaced by a nonlinear admittance function extracted from HB and connected to an external resonator or network. This enables an efficient and realistic analysis and optimization of near-field wireless power transfer, self-injection-locked radar, and tag-to-reader links without changing the oscillator design.