Calculation of Gap capacitance of zeroth order resonator

Hi all,
I have a problem calculating the gap capacitance of the Zeroth order resonator. I have simulated it for short circuited form and got the results but for open circuited case I think there is some mismatch problem hence the values of return loss are not matching. Can any one help me in this regard? I have used a quarterwave line for matching but there was no improvement in the result.
MM_DEVILS

Can attach the Zeroth Order Resonator circuit?

Can you post a diagram or the paper whose results you are trying to reproduce?