help in designing patch antenna

hii...im trying to implement a paper of w shape ground plane. He has designed if
for 2Ghz. But im arriving at value of 70mm for the length of the patch but he has taken 60. Can anyone please help me. I have tried simulating for regular patch with flat ground plane with his dimensions. But im not arriving at similar results. Can anyone please check out and tell me if the author has arrived at proper results. Please help me. I am attaching the paper