A Null Field Method-Surface Equivalence Principle Approach for Mode Analysis of Dielectric Waveguides

In a recent paper, the method of auxiliary sources (MAS) with two excitation sources (MAS-TES) was developed to compute the propagation constants of cylindrical dielectric waveguides. It was demonstrated that to ensure MAS-TES remains free from spurious solutions, both excitation sources must lie within the domain defined by an optimum curve. The null field method, when combined with the surface equivalence principle (NFM-SEP), constitutes another surface integral-equation-based method (SIEBM). It differs from MAS in that it defines equivalent currents on the physical boundary while enforcing boundary conditions on auxiliary surfaces. In this work, we introduce and employ a discretized version of NFM-SEP employing two excitation sources (TES) to perform mode analysis of dielectric waveguides. This new method is termed NFM-SEP with two excitation sources (NFM-SEP-TES). In addition, we validate the efficacy of the current vector norm (CVN) approach within NFM-SEP-TES. All obtained numerical results demonstrate that NFM-SEP-TES is devoid of spurious solutions, unlike MAS-TES, under all conditions.