A novel Doherty-like power amplifier (DPA) has been fabricated using 15 W, 2.7 GHz, GaN HEMT transistors. The quarter-wave transformer used in the classical DPA topology is replaced by a matching network including a Klopfenstein taper. From a practical prototype realization, this modification has demonstrated that the resulting DPA bandwidth (BW) is increased in comparison with the conventional topology while keeping the efficiency figures. Moreover, this design allows an
easy tuning of the group delay through the output reactance of the taper, resulting in a more straightforward adjustments than other recently-published designs where the quarter-wave transformer is replaced by multi-section transmission lines (hybrid or similar). Experimental results have shown an average efficiency of 47.2% for the HSPA+ modulation centered at 2.25GHz.
This paper presents a wideband GaN Doherty power amplifier (DPA) in the 2.6 GHz band with a 3 stages Wilkinson splitter where the impedance inverter is based on a tapered line instead of a quarter wave transformer. From the comparison with the same amplifier using a typical quarter-wave transformer as impedance inverter, and keeping both designs the same bandwidth (1.6 to 3.3 GHz, 65% of the fractional bandwidth), the Power Added Efficiency (PAE) is enhanced up to 50% (from 40.46% to 61.17% at 35 dBm input power) in the DPA with a tapered line. Besides, the transducer gain remains practically unaltered.