help me for optimizing the performance of my corrugated horn design in hfss

can anyone help me for optimizing the performance of my corrugated horn design in hfss , If yes then i will send you my design. Actually now my design gives me 35 dB Cross polarisation over 9 to 10 GHz band with low sidelobe levels (better than 25 dB). i would like to optimize cross polarization level better than 40 dB so please help me.