How to make this hfss antenna simulation frequency broader in 400-800 MHz

I have simulate a microstrip fractal antenna but the result is the vswr, and return loss still in narrow band, and the gain is too low as you can see it in the image, and i attach my project, if only someone can suggest some improvement

this the hfss file GT1802mini.zipGT1802mini.zip

thanks

hiiii
I want to ask something
Do you design your Antenna to operates in 440 MHz and 800 MHz or the second frequency is the second harmonics of the first mode?
aslo you can widen the bandwidth by Using Finite Ground Plane
thanks

well i want to design it in 440 - 800 mhz range, since microstrip antenna only cover a narrow bandwith so i will make it resonance at this range, and what kind of finite ground plane, because i'm a newbie in this topic