hfss capacitance measurement

I have to simulate interdigitated capacitor in HFSS 9.0 for my thesys and i am a beginner in hfss.
Problem is that simulations results are not as expected and are very different than results of measurement. Capacitance vs freq is measured in range 1kHz to 40Mhz. I tried to set different excitations; wave ports normally on electrode ends (rectangle 5x5mm), on top of them, lumped port in different position on electrode ends...and simulation results where different in all cases, "strange". Hfss model and dimensions of structure, without excitation and boundaries, are in attachment.

I need a help to set proper excitation and suggestion for other options to simulate this structure in freq range 1kHz to 40Mhz.

Thanks