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) http://rogersgroup.northwestern.edu/files/2018/curropneuro.pdf). 

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 opperative 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 a, for example, loop antenna in that software. If you recommend me any other software for designing the antenna, simulate it and attach it to me circuit, it would be great.

Thank you so much for reading this!