Capacitive coupling between coaxial and coplanar circular coils

Hi,
I'm currently writing my master's thesis regarding CST simulations of antennas. Obviously the coupling is an area of interest for me. Inductive coupling is already covered, but I aksed myself if there is a way to analytically calculate the capacitive coupling between two antennas.
First I assumed 2 circular PCB traces very close to each other and therefore having the same length (almost). Further there is not much difference in the traces being straight or circular. With these assumptions it is easy to find plenty of sources explaining this issue.

Now I want to calculate the capacitive coupling between two circular PCB tracks with very different radi but having the same Center and being on the same plane (coaxial and coplanar). Here I tried to find a calculation method via google and ieee explore but couldnt find any.
It would be very much appreciated if you could give me adivce where i can find Formulas regarding this or even better a source where this issue is explained/solved.

Thanks and with best regards
Richard

Formulas for this matter (even if exist) may not give you an useful answer. The best would be to have access to an EM simulator.