Modelling EM source to excite a macro cavity

In the context of geological structures I need to excite a macro cavity (dimensions of few hundred meters) like structure with a EM excitation source. In the model the cavity comprises a dielectric material with top and bottom layers are perfect electric conductors. Three lateral sides of the cavity can be considered as perfect E-Walls. From the fourth lateral side I have to excite the dielectric cavity with an EM source to set up a fundamental TE10 mode at 260kHz.

I successfully did the same with ?excitation -> wave port? in the HFSS 11. Similarly I was trying to do the same in COMSOL but I couldn?t achieve.

Would any of you can help me to model an EM source to excite the macro cavity.

Many thanks,
Otilia