suspended patch antenna array

halo i have designed a cavity backed patch antenna array at 10GHZ now the problem im facing is that when i simulate the four patches with coperate feed network i am seeing resonace at two frequancies ie is 9,3GHZ and 10.2GHz.now i have designed the cavity backed four element linear array it worked fine the distance betweem elements is 6*lamda .:S i am confused why is this happening i need help urgently