The feasibility of a variable output matching circuit in a high-power SSPA

This paper analyzes a new technique for matching the output impedance of a 100-W-class solid-state power amplifier (SSPA) to a load using a variable transformer circuit consisting of switchable series-inductor and shunt-capacitor banks. A large-signal time-domain tool (Saber®) is adapted to model the matching circuit and shows that the power-added efficiency can be made much more level with respect to input and output power than in a fixed matching circuit. For example, in a class-AB LD-MOSFET-based SSPA designed for 60% PAE at ∼110 W output, the variable matching circuit allows for ∼50% PAE down to about 20 W output, compared to about 25% PAE from a fixed matching circuit.