This paper presents switched sequential amplifiers (SSAs) using reconfigurable directional couplers as power splitters and combiners. The SSA concept allows matching the efficiency characteristics to the amplitude probability density distribution of the applied modulated signal. Therefore the back-off efficiency can be increased significantly. A three-channel SSA can e.g. theoretically achieve a −10 dB back-off efficiency exceeding 50%. Design parameters and potential efficiency enhancement are discussed for two- and three-channel SSAs. After a brief introduction of the used switched couplers, the circuit concept for two- and three-channel SSAs is described. Calculations for the possible efficiency enhancement are presented. Also signal distortions by the directional couplers are outlined. The paper closes with experimental results for a two-channel SSA.
