Bandwidth-Enhanced Doherty Power Amplifier With Optimized Quasi-Resistive Power-Combing Load Impedance

This article presents systematic research on the methodology for a wideband post-matching Doherty power amplifier (PM-DPA). First, closed-form derivations are presented to analyze the numerical solutions of the PM-DPA’s output matching network (OMN). In the presented derivations, the passive and reciprocal characteristics of the OMN are incorporated to ensure the physical feasibility of the OMN solutions, and the degree of freedom in choosing the power-combining load impedance (
$Z_{\mathrm {L.CO}}$
) is preserved to attain the mathematical completeness of the OMN solutions. The theoretical derivations prove the flexibility of
$Z_{\mathrm {L.CO}}$
in the PM-DPA for the first time. Then, the compensated semi-lumped (CSL)-
$\lambda $
/4 transmission line (TL) with absorbed transistor parasitics is proposed to take full advantage of the flexibility of
$Z_{\mathrm {L.CO}}$
in wideband PM-DPA implementation. The method of tuning
$Z_{\mathrm {L.CO}}$
with the help of CSL-
$\lambda $
/4 TL for enlarged PM-DPA bandwidth is presented. At last, prototype design of a wideband PM-DPA with optimized quasi-resistive
$Z_{\mathrm {L.CO}}$
is presented to verify the effectiveness of the proposed methodology. Measurement results show that the fabricated PM-DPA achieves the state-of-the-art performances, such as the gains of 12–13 dB, the saturated output powers of 43.6–45 dBm, the drain efficiencies of 62%–71% for saturated operation, and drain the efficiencies of 49%–58% for 6-dB power-back-off (PBO) operation over 1.4–2.5 GHz.