capacitor on PCB using ADS

I want to design a capacitor in @DS as the capacitors available in the component libray have SRF around 6-7 GHz but i need a capcitor working till 11 GHz so can some one tell me how can i design it and how much time will it take as i have very short time.

the substrate parameters are :
Material : Rogers
Er = 3.48
Loss Tangent = 0.004
Dielectric Thickness = 250 um
Thickness of metal = 70 um

thanks in advance.

/k