为了应对移动通信系统多模式兼容和节能高效的需求，本文在经典Doherty功放的基础上引入双频传输线实现了双频Doherty功放的理论分析和设计，双频传输线是一类在两个频率具有特定阻抗变换性质结构的统称。 经典Doherty功放能够在功率回退一定范围内保持基本恒定的高效率，本文实现的双频双路Doherty功放能够在两个不同工作频率实现这样的特征，这两个工作频率在一定的频率比范围内可以任意设定，并且本文实现的双频双路Doherty功放能够在两个工作频率并发同步工作。使用Cree公司生产的CRF24010型碳化硅(SiC)金属-半导体场效应晶体管(MESFET)，本文制作了双频双路Doherty功放，在0.88GHz和1.96GHz饱和输出功率分别为41dBm和40dBm，饱和效率分别为51%和48%，在功率回退5dB点效率分别为38.8%和38%。 本文在双频双路Doherty功放的基础上作了进一步改进，得到了双频多路Doherty功放的理论和设计方法，能够同时在两个工作频率功率回退更大的范围内保持基本恒定的高效率。使用Cree公司生产的CRF24010型SiC MESFET，本文制作了双频三路Doherty功放，在0.92GHz和1.99GHz饱和输出功率分别为41.5dBm和41dBm，饱和效率分别为47.6%和46.4%，在功率回退8dB点效率分别为33.3%和30%。 为了在不同的工作频率下维持功放工作点不变，本文提出了非平衡双频Doherty功放的理论和设计方法，在两个工作频率上使Doherty功放的表现性能接近理想。使用Cree公司生产的CGH40010型氮化镓(GaN)高电子迁移率晶体管(HEMT)，本文制作了非平衡双频三路Doherty功放，在0.9GHz和2.31GHz饱和输出功率分别为46dBm和45.5dBm，饱和效率分别为66.8%和56.6%，在功率回退9dB点效率为64.6%和43%。 为了拓展双频Doherty功放的工作带宽，本文分析了双频传输线对双频Doherty功放带宽的影响。仿真结果显示双频传输线比普通传输线的带宽要窄，对功放带宽有一定限制。

In this paper, a series of dual-band Doherty power amplifier (PA) are proposed by introducing dual-band transmission lines to a classic Doherty PA. The dual-band transmission line is a topology that has determined equivalent characteristic impedances and electric lengths at two different frequencies. A dual-band Doherty PA keeps a high efficiency at an output power back-off range at two operating bands concurrently. Base on the SiC MESFET CRF24010 made by Cree corp., a prototype of dual-band two-way Doherty PA is fabricated. The measured results show that an efficiency of 51% and 48% is reached at the saturated output power of 41dBm and 40dBm at 0.88GHz and 1.96GHz, respectively. And at the 5dB output back-off point, the efficiency is 38.8% and 38% at 0.88GHz and 1.96GHz, respectively. To keep a high efficiency at a wider output back-off range, a design method of dual-band multi-way Doherty is proposed. Base on the SiC MESFET CRF24010 made by Cree corp., a prototype of dual-band tri-way Doherty PA is fabricated. The measured results show that an efficiency of 47.6% and 46.4% is reached at the saturated output power of 41.5dBm and 41dBm at 0.92GHz and 1.99GHz, respectively. And at the 8dB output back-off point, the efficiency is 33.3% and 30% at 0.92GHz and 1.99GHz, respectively. To keep a constant quiescent operating point at different band, a design method of unequal dual-band Doherty is proposed. Base on the GaN HEMT CGH40010 made by Cree corp., a prototype of unequal dual-band tri-way Doherty PA is fabricated. The measured results show that an efficiency of 66.8% and 56.6% is reached at the saturated output power of 46dBm and 45.5dBm at 0.9GHz and 2.31GHz, respectively. And at the 9dB output back-off point, the efficiency is 64.6% and 43% at 0.9GHz and 2.31GHz, respectively. A theoretic analysis on the band-width of the dual-band transmission line and the dual-band Doherty PA is made at the end.