dual band antenna frequency shift

Hi Gurus

I am working on dual band patch antenna.

Getting first resonance at 2.45Ghz

Modified patch to get second resonance at 4.5GHz

Now, when I re-simulate the modified patch at 2.45GHz. The resonance frequency has shifted to 2.2GHz.

Can anybody comment on that , is it normal or something I am doing wrong.

This is first time I am doing dual band so not much idea

regards

It is perfectly normal. In dual band patch antennas when you tune one frequency, it is normal to produce small shifts in the other frequency.
You'll need to fine tune the design monitorizing both frequencies.