tanx but I think you didnt understand my question ! firstly in eigenmode solution type we are not allowed to use excitations secondly i have drawn a rectangular waveguide with these dimensions 2.286 cm & 1.016 cm . I want to know exact cutoff frequencies :-( first cutoff frequency is about 6.5 GHz and second one should be about 13 GHz but in eigenmode data i cant see these cutoff frequencies !! aren't resonance frequencies the same as cutoff frequencies? where is the problem?:roll: