Broadband Doherty Power Amplifier Based on Asymmetric Load Matching Networks

This brief presents asymmetric load matching networks for broadband Doherty power amplifiers (DPAs). The output combiner consists of two λ/4 impedance transformers with optimized characteristic impedance values in order to provide a load modulation at a high output power level; the bandwidth limitation for efficiency at the back-off power level can be then mitigated. For a proper load modulation with the proposed output combiner, asymmetric load matching networks between the carrier and peaking amplifiers are proposed. The input and output matching networks were designed using balanced open stubs, which are more insensitive to frequency than unbalanced open stubs. For the load matching networks, two-section matching networks were adopted. The designed and implemented broadband DPA showed a fractional bandwidth of 23.5% (from 750 to 950 MHz). It also showed measured efficiency values of higher than 55.4% at the peak power level and 51.5% at the 6-dB back-off power level, respectively. For the operational frequency range, a peak output power value of higher than 48 dBm and a gain of 14-15.8 dB were achieved.