differentially-driven aperture coupled microstrip antenna

Hi,

Based on my understanding after reading these two IEEE papers, i have came up with what i think a differentially driven aperture coupled microstrip structure would look like. Can someone pls help to review my design and tell me what is wrong with it? I am not unable to achieve the return loss response at the correct resonant frequency that is intended. I'm am designing this antenna at 2Ghz using FR4 as the patch and the feed substrate with thickness 1.6mm and dielectric constant of 4.4. i'm attaching my design below as well as the reference IEEE papers that i based my calculations on for your reference. Please help....thanks