Equivalent circuit for a real capacitor
If we had an FFT amplitude and phase, one could get a perfect passive model of all the elements, knowing that the source is 50Ω and thus the transfer function.

The signal has the following characteristics from which a model can be generated.  


Slew rate dV/dt= 200mV/1us or dt/dV=5us/V  (*)
ΔVin=10Vpp thus with 50Ω source 
ΔIc=10V/50Ω=200mA 
Vpp= 200mV but asymptotic slopes of Vout project to 222 mVpp thus 


fundamental dt/dV becomes 4.5us/V (*)   



Since C=Ic dt/dV = 200mA * 4.5us/V = **0.9 uF and not 2.2 uF**

However with a simulator you can model the waveform and adjust the parameters.
From this I get RLC1= 0.6uF+ 20nH + 50mΩ and RLC2 = 0.8uF + 0nH + 300mΩ (in //)



It is either  Rs=100 Ohm source and 1.8uF or 50 Ohm source and 0.9uF with an ESR=50mΩ approx with about 20nH of ESL and many other RLC smaller networks shunting the RL network.







simulate this circuit &ndash; Schematic created using CircuitLab

This is also why C(f), ESR and ESL changes value with sine frequency due to reactance model.  But SRF and PRF will give a better model and a scatttering s22  plot is the best from the OEM.