Characteristic mode analysis (CMA) is based on time-harmonic electromagnetics and applied mostly in frequency domain. In this paper, CMA is extended to time domain (TD) for transmission problems. Based on the modal self- and mutual-admittance of two-port systems, the modal TD response is obtained using inverse fast Fourier transform, extrapolation and Hilbert transform. TD-CMA represents modal impulse response on specified ports, and impulse response of the system is the linear superposition of the modal ones. Numerical examples are provided to explain this new concept. For a pair of parallel wires, the calculated TD-CMA is alike the common and differential modes. For a pair of dipoles, TD-CMA can be divided into strong and weak coupling modes according to their magnitudes. The strong coupling modes are due to the pulse radiation and oscillations at dipole tips and feedings. Time delay paths are clearly observed in the near field but are not discernable in the intermediate field. This shows different coupling mechanisms for the two cases. TD-CMA expands research field of CMA and may find applications for analyzing transient behaviors of microwave systems.

中文翻译：

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传输问题的时域特征模态分析


特征模式分析（CMA）基于时谐电磁学，主要应用于频域。本文将CMA扩展到时域（TD）来解决传输问题。基于二端口系统的模态自导纳和互导纳，利用快速傅里叶逆变换、外推法和希尔伯特变换获得模态TD响应。 TD-CMA表示指定端口上的模态脉冲响应，系统的脉冲响应是模态脉冲响应的线性叠加。提供了数值例子来解释这个新概念。对于一对平行线，计算的 TD-CMA 与共模和差模相似。对于一对偶极子，TD-CMA根据其大小可分为强耦合模式和弱耦合模式。强耦合模式是由于偶极子尖端和馈电处的脉冲辐射和振荡造成的。在近场中可以清楚地观察到时间延迟路径，但在中场中则无法辨别。这显示了两种情况的不同耦合机制。 TD-CMA 扩展了 CMA 的研究领域，并可能在分析微波系统的瞬态行为方面找到应用。