S11 Ripple/Oscillations in CST Simulation - Seeking Advice

[yotamen]

I'm running a simulation in CST Studio Suite, and I'm seeing a lot of ripples/oscillation in my S11 plot. I'm trying to get a smoother curve to better understand my resonant cavity performance. I've attached a screenshot of the S11 plot

Im not sure what is causing this oscillations, when i run the same simulation in HFSS the line is smooth

Thank you for your time
P.S (im new to cst studio so it might be a settings problem but honestly i dont know where to even start looking)

 

[dick_freebird]

"passband ripple" is a thing, but this looks like
maybe numerical solver algorithm & settings.
Or, mesh coarseness? Like "lumped elements"
too lumpy, brings resonant frequencies into
band when finer grained they would be "way
out to the right"?

 

[yotamen]

I changed solver accuracy to -80 dB (from -40) and number of pulses in special to 100 (from 20) and it smoothed some of the resonance