Computational difficulties related to Green´s functions for longitudinal current sources radiating inside waveguides and cavities

This paper describes computational difficulties, which arise within the IE-MoM approach when calculating reaction integrals related to longitudinal current distributions radiating inside waveguides or cavities. The difficulty consists in fast reaching the double precision floating point overflow before convergent results are obtained. This numerical instability prevents us from using higher number of modes (more than 10E+03 modes) in the numerical evaluation of modal series. The origin of such behavior is explained and a method for overcoming the described problem is proposed. It is shown that the method enables more than 150E+03 modes to be used without approaching the floating point overflow.