I am trying to simulate a simple graphene printed dipole antenna with HFSS. Because of frequency dependent conductivity of the graphene, the antenna is very small in comparison to lambda/2 metallic dipole and it should operate with surface plasmon TM mode. I use lumped port excitation. The problem is that I can't find the resonance of the antenna. Which challenge with similar designs should be taken into account ? What do you recommend to check and might be wrong to get accurate results?