Thanks cwin; You are right, that way I'll get the S-parameter between two poerts of required modes. Now my problem is little different. Suppose a step transition in circular w/g and thus it is converting from dominant TE11, TE11* mode to TE11, TE11*, TM01, TE21 & TE21*. If I give input power of 1mW, how will be distribution of power among different modes. Actually we excite by coaxial to w/g transition.
I can plot gamma factor in HFSS, but how to get the power? Hope I am clear about my problem.