利用辐射场诊断模式成分的病态特性

 根据辐射场测量并确定已知尺寸和工作频率的波导内可能存在的模式(即模式诊断)是一个电磁逆问题。针对该逆问题，利用电磁分析软件计算过模圆波导馈电圆锥喇叭天线的远区辐射场，通过比较多种模式以不同比例组合馈电产生的总辐射场之间的差异,研究模式诊断逆问题的病态程度。结果表明该逆问题病态严重，模式成分比例变化很大，但某些位置上辐射场变化较小甚至没有区别，即辐射场对各模式比例变化不敏感。如果在这些位置上测量则很难判断出各模式的成分，只有通过增加信息量才能缓解病态的严重程度，得到较准确的结果。通过分析，给出了对各模式组合比例变化敏感的测量位置。

Ill-posedness of inverse problem about mode content determination using far field measurements

The ill-posedness of the inverse problem on determination of mode content in a multimode cylindrical waveguide using far field measurements is investigated in this paper. The radiation patterns of different mode radiated from a conical horn antenna fed by a multi-mode waveguide are calculated. Then the ill-posedness of the inverse problem is investigated by comparing the radiation pattern generated by different hybrid modes. Results show that the inverse problem is severely ill-posed, because the far field at certain positions is not sensitive to the variation of the mode contents. It is difficult to determine the mode content accurately according to the measurements at those positions. After analyzing the change of far-field with the variation of mode content, the positions where measurem