Recently we have proposed a finite element based eigenanalysis for lossy and unbounded structures. Our present effort aims at the validation of this technique for the study of complex radiating structures like the cavity backed type. The typical Absorbing Boundary Condition (ABC) of 1st kind is employed, while finite conductivity is introduced at the metallic parts of the studied structure. The spurious modes are being suppressed by the enforcement of 'divergence-free' constraint equations in the whole domain. It is proved in the current work that the non-physical modes restriction of the solution domain is achieved only by the projection of the seeding vector in the null space of the irrotational field, during the linearization procedure.
