First you have to choose a substrate to build the patch on, because the er of the material defines the size of the patch. Then you have the thickness and the er you can calculate the length of the patch. Theoretical the size is lambda/2 for 60 GHz it is 2.5 mm (in the case that the isolator is air er=1) this is very small. If the er is greater , for example 2 the size ist sqrt(2) smaller.
Yes. I am calculate the length and width which is 1.6mm and 1.9mm. The substrate i used is duroid Er =2.2. I dun understand the size is lamda/2, it is theory but how to relate to the length?
I agree with Vfone. I would start out with a 900 MHz Patch antenna and desing it in HFSS or another tool, verify the design in real life and go from there. And good luck.