A Ka-Band GaN Doherty Power Amplifier with High Efficiency Over a Fractional Bandwidth of 20.4%

This paper presents the design and implementation of a Ka-band Doherty power amplifier (DPA) fabricated on a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.1 \mu \mathrm{m}$</tex> gate-length GaN-on-SiC HEMT technology. The DPA achieves a fractional bandwidth (FWB) of 20.4% associated with high power-added efficiency (PAE). This circuit bandwidth extension emanates from adopting an impedance inverting network incorporating the transistor's equivalent output capacitance and operating the Main and Auxiliary transistor under maximum output power instead of maximum PAE loading. On-carrier, continuous-wave (CW) measurements performed on the DPA from 22.5 to 27.5 GHz show that the DPA delivers a saturated output power of 31.1-32.4 dBm associated with a peak PAE of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$23.6-38.8 {\%}$</tex>. At 6 and 8 dB output power back-off (OPBO), the DPA achieves a PAE of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 2. 8 - 2 9 \%}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 0 - 2 3. 2 \%}$</tex>, respectively. To the author's best knowledge, this is the broadest circuit bandwidth reported on GaN-DPAs at Ka-band.