how to increase the gain of microstrip antenna

hello
i have designed and simulated a micrpstrip antenna by using Ie3d
the parameters i m getting are
Fr=6.51
returnloss =-30.86
reflection coffient =0.03
mismatch loss =0.00
vswr= 1.06
directivity is 7.56 dbi
gain= 2.56 dbi
gain is very low

so i want to ask that what is the range of the gain and how can i increase the gain my antenna
plz guide me in this
i will be very thankfull to you

regards sameer

increase the cell number

You have good directivity so one would expect your gain to be higher. Gain can be adversely affected if your ground plane is small or radiation efficiency is low (related to impedance). Try increasing the size of your ground plane.