The microstrip capacitor design (distributed element)

Hi guys,

I'm working on some RF microstrip project. This is my first steps in this kind of things so I need some help from you...
Ok, so let we go to the begining. I started from really simple task - I designed quarter wave transformer (it's nothing else like the stripline so...). After that, I decide to add to this line some rectangular shape (as a capacitor). And now I want ask you - how can I calculate dimensions of this shape for some fixed value of capacitance ? (for e.g. 0.12pF).
I'm sending you an example :
https://upload.wikimedia.org/wikiped...ass_form_2.svg

According to these link - how can I calculate dimensions of C2, C4 or C6 if I know values of capacitance each of those shapes? I guess that there are some equations to doing it.

I will be really greatful for any help.
B. Regards,

http://www.rfcafe.com/references/ele...components.htm