基于实频技术的高效率宽带功率放大器研究

The power amplifier with high-efficiency and broadband simultaneously is extensively utilized in many domains, such as the military radar communication, the outer space microwave transmitter and the emerging next-generation wireless communication system. From the transmitter point of view, the performance of the power amplifier, which is decided by the matching network, strongly influences the overall transmitter system. In order to solve the matching problem of the high efficiency and broadband power amplifier, the physics model of gallium nitride (GaN) wide bandgap semiconductor is modeled and analyzed for two reasons. For one thing, the distributed characteristic properties of the fundamental impedance, the second and third harmonic wave are operated in the one-octave or even wider frequency range; for another, the mechanism of intermodulation distortions excited by various kinds of small or large signals is investigated and the intermodulation cancelling technology is used to optimize IM3 and IM5. The simplified real frequency technology is employed to synthesize the best matching network based on the S-parameters of the GaN transistor, which is from the previously mentioned models. The lowpass matching network with the composite left/right hand metamaterials is adopted to realize the matching network calculated by the real frequency technology of the power amplifier. Experiments will be designed to verify the feasibility of the high efficiency broadband power amplifier. Meanwhile, a transmitter with the pre-distortion component for TD-LTE communication will be demonstrated. The preliminary investigation of simulation by Agilent Advanced Design System (ADS) shows that in the 2-4GHz band for the Cree CGH40010 of the GaN transistor can keep the power added efficiency (PAE) higher than 50% with ripple less than 2dB.

在军用雷达通信系统、空间微波传输系统和下一代无线通信系统中，功率放大器面临同时具备高效率和宽带宽的挑战。为了解决高效率宽带微波固态功率放大器中的带宽匹配问题，本项目拟通过建立和分析GaN宽禁带半导体器件的物理模型，掌握GaN晶体管在倍频程甚至更宽的带宽内的基波阻抗和二次及三次谐波阻抗分布特征；掌握GaN晶体管在各类信号驱动下的交调失真机理并进一步提出交调失真优化方案。随之根据GaN晶体管阻抗特性，采用实频分析技术构建最佳匹配网络结构，并利用基于左右手复合材料的低通匹配网络的技术方案实现高效率宽带功率放大器。最后通过实验验证高效率宽带功率放大器的可行性，并联合预失真技术制作可用于TD-LTE通信的发射机演示样机。初步的仿真数据表明，对于Cree公司的CGH40010 GaN晶体管，在2-4GHz的工作频带内可以保持附加效率高于50%，带内波动小于2dB。

本项目围绕提高固态功率放大器的带宽、效率和线性开展了系统性研究。带宽、效率和线性作为功率放大器最重要的三个方面，其特性相互制约。针对这一难题，本研究采用非线性电路理论方法，分析晶体管的非线性特征，完善晶体管的非线性模型，利用谐波控制改进晶体管的输出波形，最后通过实频技术综合出匹配网络。研究结果表明，本项目相关工作可以显著提高功率放大器的带宽、效率和线性，相应学术成果已发表在IEEE Transactions on Microwave Theory and Techniques、IEEE Transactions on Circuits and Systems等国际期刊，得到国内外同行高度好评，并与华为、爱立信等业界知名厂商合作，将研究成果应用于4G、5G无线通信基站。.在功率晶体管非线性特征分析的研究方面，基于晶体管的非线性等效模型，分析并仿真验证了功率放大器的谐波成分以及偏置条件对线性度的影响，得到了兼顾效率与线性的阻抗条件，提出了通过谐波调谐实现高效率线性功率放大器的解决方案。.在实频技术匹配网络综合的研究方面，提出了扩展的切比雪夫函数（准切比雪夫函数），使得在相同阻抗转换比和阻抗函数阶数的情况下，可产生一族准切比雪夫曲线，从这一族阻抗函数中移出的第一个元件值分布在较大的数值空间内，合理选择该元件值，就能使晶体管的输出等效阻抗作为匹配网络的一部分，从而使得所选择的阻抗函数满足功率放大器的阻抗匹配要求。.在谐波控制对功率放大器性能影响的研究方面，系统分析了谐波成分如何决定功率放大器的输出功率、带宽和效率，给出了具体的阻抗数值解空间，提出了多种基于谐波控制的连续型宽带高效率功率放大器解决方案，并将连续型功率放大器应用于Doherty功率放大器的设计之中，总结出了连续型Doherty功率放大器的设计方法，在保证高效率的前提下，有效地拓展了Doherty功率放大器的带宽和动态范围。