I am designing a bioimplantable circuit for a biomedical implant. The goal is to have an extremely tiny device in a flexible substrate (Dupont Pyralux) that must be powered wirelessly. 

My problem comes here. I do not have much knowledge about antennas. I have been told to design an antenna that must work at 13.56 MHz. I am following the design of John Rogers (page 5, figure 2,b), [Implantable, wireless device platforms for neuroscience
research][1]. 

Then I have some doubts about the design that I would like to receive some feedback about it. 

 - How would you design a PCB antenna with that operating frequency (13.56 MHz)?
 - How would you address this problem? I need a primary and secondary coils working in that frequency.

I use Eagle but I don't know how to design, for example, a loop antenna in that software. If you recommend to me any other software for designing the antenna, simulating it and attaching it to my circuit, it would be great.



  [1]: http://rogersgroup.northwestern.edu/files/2018/curropneuro.pdf