功率合成电路在氮化镓放大器中的应用

针对氮化镓大功率放大器,由于传统1/4λ枝节线的电桥互耦造成放大器的直流自激和低频自激,在传统1/4λ传输枝节的Wilkinson电桥的基础上,结合氮化镓器件尺寸,设计出以3/4λ传输枝节的Wilkinson电桥为功率分配器/合成器。其输出端口尺寸为27.2mm。在8GHz～9GHz内,插入损耗<1dB,输出端口隔离度>14dB,端口回波损耗>9dB。利用实验室自制的SiC材料衬底的2.5mm栅宽GaN HEMT器件为放大单元,设计完成了两路合成放大器,在8GHz连续波条件下,放大器饱和输出功率为41.46dBm,合成效率为82.3%。通过分析发现,放大器合成效率的下降主要是由每路放大单元特性不一致和功率合成网络损耗所造成的。

Application of Power Combining Circuit on GaN Amplifier

In band of 8 GHz～9GHz,because the traditional 1/4λ branch of 3dB hybrid causes self-oscillatian and crosstalk of low-frequency for GaN high-power amplifier due to the mutual coupling,3/4λ branch of 3dB hybrid was designed based on the packaged size of AlGaN/GaN HEMT.The size of output of 3dB hybrid is 27.2mm.In this band,the insertion loss is less than 1dB,the isolation of output is more than 14dB and the return loss is more than 9 dB.And then,a two-way combined amplifier was fabricated based on AlGaN/GaN HEMT with 2.5mm gate width technology developed by our Lab on SiC substrate.At 8GHz and under CW operating condition,the amplifier module exhibits output power of 41.46dBm and the combined efficiency of 82.3%.The reduction of combining efficiency may resulted from the non-identical GaN HMET and the loss of hybrid coupler.