根据耦合波理论,推导出轴对称渐变波导中,考虑波导壁损耗时的多模传输时域耦合波方程组,并给出该方程组中各模式间耦合系数的具体表达式。据此编写了渐变波导中多模传输特性数值模拟程序。利用该程序计算了在THz波段圆波导中的模式衰减,在THz波段研究波导中的多模传输特性时,必须考虑波导壁的阻抗损耗影响。数值分析了直波导中的模式耦合问题,从而证实了波导壁有限电导率能产生模式耦合这一耦合机制。介绍了利用该程序数值分析波导耦合器和过渡器中多模传输特性的两个例子,利用该程序可对波导耦合器和过渡器中的多模传输特性进行数值模拟分析,进而对结构进行设计和优化。

Based on the theory of mode coupling,the paper deduced the time-dependent coupling-wave equationd that the modes satisfy in tapering circular waveguide,and presented the expressions of coupling coefficients of the equations. The metallic wall loss was considered in the process. According to the equations,we write a code for simulation of the multimode transmission property in tapering circular waveguide. Firstly,using the code,mode loss in circular waveguide in THz region was computed.It is found that when studying the multimode transmission property in tapering circular waveguide,the effect of metallic wall impedance loss must be considered.Secondly,we analyzed mode coupling numerically. This attests to the existence of the coupling mechanism due to fininte conductivity of the metallic wall. Lastly,we present two other examples for operation of the code,namely waveguide coupler and waveguide transition. The examples demonstrate that,using the code,we can analyze the multimode transmission property in tapering circular waveguide such as waveguide couplers and waveguide transitions,etc. This would benefit the design and optimization of structure.