wide band printed dipole antenna

Hello,

i am designing a microstrip dipole on the frequency between 900 Mhz and 2200 Mhz . i did something about it in Hfss with lumped ports but i should realize it physically.And when i did it with lumped ports it have not a omnidirectional pattern . so what can be the problem fot this? i didnt use a balun is it a problem for this?

thanks