CPW Feed squre Slot Antenna

Hi Every one

I have shifted the operating frequency of CPW-Fed Square Slot antenna from 3.2 GHz to 2.45 GHz by increasing its all dimension sizes by 1.3 mm. However, the gain has been reduced from 4.5 dB to 1.5 dB.

Is there any technique or idea that I can used to increase the gain ?

my best regards