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A dual-band tri-way Doherty power amplifier (PA) with frequency dependent power division is proposed. Compared to the dual-band two-way Doherty PA, the power back-off range of the dual-band tri-way Doherty PA is extended efficiently. Due to frequency dependent power division, the efficiency of the proposed PA is improved at two different frequencies concurrently. The measured results show that power-added efficiencies of 61 and 44% are reached at the 9 dB back-off point from saturation at 0.9 and 2.31 GHz, respectively.
Introduction: The power amplifier (PA) is the last stage in a transmitter in mobile communication systems. To meet the demands on green radio and multi-band operation in mobile communication systems, high efficiency and multi-band PAs are required. The Doherty PA, which was first proposed in [1] by W. H. Doherty in 1936, is a significant approach to high efficiency. Recently, different design methods of Doherty PAs were introduced [2, 3] to approach an ideal Doherty performance. Based on the topology of the Doherty PA and dual-band components [4, 5], a dual-band Doherty PA was proposed in [6, 7], followed by further work in [8 -10].In[10], a dual-band tri-way Doherty PA based SiC MESFET with an equal power divider was designed while its output back-off range was small.
In this Letter, a dual-band tri-way unequal power divider is introduced into the dual-band tri-way Doherty PA and a GaN HEMT is used instead of an SiC transistor as in [10]. To the best of our knowledge, this proposed work has the highest first peak efficiency and the widest output back-off range at two different operating frequencies.
Theory and design methods: Fig. 1 shows the topology of the proposed dual-band tri-way Doherty PA which consists of a carrier PA, two peaking PAs, a tri-way power divider, offset lines, delay lines and quarter-wavelength lines. All the components in this proposed structure are dual-band components which have been introduced in [10], except that the tri-way power divider is realised by a qua-way power divider composed ofan unequal Wilkinson powerdividercelland two equal Wilkinson power divider cells. The input power division is...