Evaluation of Green´s Functions of Rectangular Cavities Around Resonant Frequencies in the Method of Moments

This letter presents a technique to evaluate the Green´s functions of rectangular cavities around resonant frequencies. It is well known that, lossless cavities´ Green´s functions are singular at discrete resonant frequencies hence cannot be numerically evaluated directly. In this letter, the singular terms are first explicitly separated from the Green´s functions, and then a bases rearrangement method is proposed to avoid direct evaluation of singularities in the context of the method of moments (MOM). Consequently, MOM that conventionally fails around resonant frequencies yields correct results for all frequencies. The singularity evaluation technique is validated through a practical example. Good agreements between MOM and experimental data are demonstrated over a wide spectral range including various resonant frequencies.