Did you try tuning the Parameters of your design to tune out the parasitic and any impedance mismatch?

You may try shifting the feed location

Please share some snaps from your design to get insight. Happy to help you.

Hello,

Could you please share the result of S11 which is obtained. Because there are several reasons not to achieve S11 less then -10 dB. First check feed position. Second check boundary conditions. Third check parameters, is it compatible with wavelength. Fourth check meshing of the software. Fifth check height of substrate and many mores reasons.

Thanks,

Hello,

I guess you are talking about simulated results. When trying to get a good impedance match, in a single port antenna, check your Z11 parameters and tune parameters such that the imaginary part of Z11 is close to zero while the real part is close to 50 Ohm (assuming a 50 Ohm (normalized) feed). Typical tuning parameters, as mentioned by others, include feed position, feed line impedance etc. It would depend on type of feeding geometry you have adopted.