Design of a concurrent quad-band GaN-HEMT Doherty power amplifier for wireless applications

This paper presents the design and measurement results of a quad-band Doherty power amplifier (DPA) for concurrent operation in the 900 MHz, 1.5 GHz, 2.1 GHz and 2.6 GHz frequency bands. In principle, a quad-band DPA requires that all passive structures involving the DPA, but especially the impedance inverter network (IIN), be either broad-or multiband to cover the desired number of frequency bands. In this work, a newly developed multiband IIN is introduced, enabling the realisation of multiband symmetric and asymmetric DPAs. The design concept can theoretically be applied for a large number of frequency bands. The approach has been validated in hybrid technology using a 10 W and 25 W GaN-HEMT as carrier and peaking devices, respectively. The measured results show peak drain efficiencies of 58.12 %, 60.52 %, 52.74 %, and 43.3 %, associated with output powers of greater than 41.75 dBm in all four bands. The corresponding drain efficiencies at 6 dB output power back-off are measured to be 48 %, 56 %, 47 % and 31.8 % for the first, second, third, and fourth band, respectively. To the best of our knowledge, this is the first time a quad-band concurrent DPA has been successfully designed and implemented.