Broadband SLMBA Design Including 90° Hybrid Frequency Response Using an Automatic Methodology

This article proposes an automatic methodology for the design of a sequential load-modulated balanced amplifier (SLMBA), which takes corrections for its output combiner’s (a 90° hybrid) frequency response. The method uses a properly selected control amplifier phase to compensate for the 90° hybrid frequency response and finds the accurate impedances that are observed towards the hybrid. Based on this, and on a multi-dimensional search performed over the control and balanced devices’ load-pull data, the optimum termination impedance profiles are found, considering the desired output power levels and efficiency. The balanced power amplifiers off-state impedance is also incorporated in the methodology to prevent the otherwise unavoidable SLMBA performance degradation. Consequently, three scattering parameter matrices are obtained in a polynomial form, corresponding to the output matching networks of the balanced and control amplifiers, and the required post-matching network at the
$50~\Omega $
output port. Finally, the method is validated with a practical SLMBA implementation, synthesizing real matching networks that realize the derived S-parameter matrices.