Microstrip Patch Antenna at 3.5GHZ...Need helps

Hi,
I am designing the patch antenna by using ADS 2006.
Operation frequency = 3.5Ghz
substrate is FR4
fo 3.5GHz
ε r 4.5
ε eff 4.0935
W 25.84mm
L 19.78mm
thickness of substrate h 1.6mm
thickness of copper t 0.035mm

But the simulation result for s parameter show that resonant frequency is at 7.5Ghz(lowest loss return)
What should I do next? change the dimension of patch antenna? or the feed line ?

What is the most suitable value for the mesh density (cell per wavelength) ?

Hi.
I have simulated the patch with dimension W 25.84mm, L 19.78mm, which is fed by coaxial probe, and have obtained next results

I assume, that need to change dimension of the feed line and width of patch.