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First, I think you know that you are sure that there will be no ground plane on your loop antenna. Otherwise, it will not work.
Second, if you have HFSS, that is going to be very easy. Just put your trace on the pcb substrate.
Third, if you have no HFSS, you can still be able to do it. Find a textbook, trying to find an easy equation (without pcb). It should be close to your desired antenna. Then you can adjust your design. The pcb will just shift the resonant frequency a little bit.
I hope this will help you.