In this paper, an extensive review of the most up-to-date papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important trend is the bandwidth enlargement of the Doherty architecture, that involves a large number of papers. Multi-band, multi-mode solutions are also considered, using either fixed or reconfigurable solutions. The final section is dedicated to the most significant Doherty integrated implementations.Index Terms-Doherty power amplifier, gallium arsenide, gallium nitride, linearization, wireless communications.

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A quarter-wavelength impedance transformer as well as a number of other factors limit the bandwidth (BW) of Doherty power amplifiers (PAs). We utilize the lower Q of a quarter-wavelength transformer and propose a phase compensation circuit and an additional offset line to be incorporated into the matching networks for an enhanced BW of the Doherty PA. The quarter-wavelength transformer and the final output circuit have the same . Input dividing networks are also analyzed for operation of broad BW. The Doherty PA for long term evolution (LTE) applications is integrated into a 1.4 1.4 mm 2 die using an InGaP/GaAs heterojunction bipolar transistor (HBT) process. For an LTE signal with a 7.5-dB peak-to-average power ratio (PAPR) and a 10-MHz BW, the PA with a supply voltage of 4.5 V delivers a power-added efficiency (PAE) of 36.3% and an adjacent channel leakage ratio (ACLR) of 32 dBc with an average output power of 27.5 dBm at a frequency of 1.85 GHz. Across frequencies from 1.6-2.1 GHz, the PA performs with a PAE of more than 30%, a gain of more than 28 dB and an ACLR of less than 31 dBc at an average output power of 27.5 dBm while satisfying the standard spectrum mask. These figures verify that the proposed bandwidth enhancement techniques are effective for handset Doherty PAs.

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