plz help me in designing this design using IE3D

hello friends, i m sameer again, i want to design a rectanglular microstrip antenna in which corners are truncated. i have attached the picture of desig. i have to make this design using IE3D, so please somebody help me step by step procedure of designing it,as i m new to IE3D and just learning working on IE3D.
i know how to feed the recatangle but i dont know how to cut the corners
so plz help me in this. i will be very thankful to you
regards
sameer