Multiband antenna problem

Hi

Does anyone have an experience in multiband antennas? I use hfss 13.0 and simulate a microstrip antennas form papers(training)when I simulate a single frequency it works well but when there are several bands I mess things up. I get some bands and miss others.
what factors are crucial in generating the resonances in the antenna structure( other than the dimensions of the antenna. structure is already designed) the problem is in me simulating -I GUESS- correct me if I'm wrong.
(is it air box, meshing, ground plane ?)


pls help.
thnx

As long as your structure creates field resonances, it is a mode. However, such resonance can be various depending on your structure, for example, dipole antenna's resonances can be calculated by hand, same to rectangular or square patch antenna, however, when your geometry is not that regular, then full-wave simulation is needed. You need to demonstrate your structure and show the result before getting a further answer.

If you like I'll send you the hfss file. the results and the reference graph.

Thank you