Characteristic mode and reduced order modeling at low frequencies

Abstract

Recent resurgence of interest in characteristic mode analysis (CMA) significantly enriches the tool set for the analysis and synthesis of complicated scattering and radiating systems. The theory of CM was first introduced by Garbacz and Turpin [1] to diagonalize the scattering matrix of a conducting object. Later, it was refined by Harrington and Mautz [2] to form a weighted eigenvalue problem by invoking the impedance operator, which relates the induced surface current to the tangent component of the incident electric field on the body surface. Since its inception in the early 1970s, CMA has been mainly investigated in the resonance regime. Although CMA has been adopted in small antenna design where a small number of modal currents are the major contributors of the radiation field [3], it is less well known how CMs behave at even lower frequencies. Only a few works can be found dealing with low-frequency (LF) CMA in the literature, e.g., Schuman and Harrington [4] studied the LF expansion for CMs of conducting bodies with a perturbation approach. Regarding aperture coupling problems, Leviatan [5] researched on LF CMs for the equivalent magnetic current using generalized admittance operators.