圆极化器中高次模对轴比的影响

    小弟现在在仿真一个圆波导中的螺钉圆极化器，但是圆波导的电尺寸较大，高次模TM01、TE21、TE01和TM11模都可以传输。我现在就是不知道怎么考察或计算这些高次模对圆极化器轴比的影响（我从论文上看到的轴比计算公式好像是只针对主模的）...
PS：1、从仿真结果看，由主模激励起的高次模传输系数S2(n),1(1)都在-25dB以下，是不是就可以不用考虑由主模激励起的高次模对轴比的影响啦?
          2、由于圆波导电尺寸较大，如果激励端口本来就有高次模，怎么考察或计算这些高次模对轴比的影响呢?
    小弟才疏学浅，望各位大侠给点建议吧，小弟感激不尽

first one
the fact is not familiar with what you said,-25db is the level of cross-polarization. if the  excitation is the main mode, the purpose you addressed is correct. those evanescent mode will vanish in a certain distance which is yield to the vector of wave. if the distance is large than the distance which is in your project, it should be considered.
second one
you can port a high mode, and get the frequency response. due to the proportion of different modes's energy, the final respone can be handled.

Thank you very much for your explaination！