[SOLVED] Reactive near field vs Radiating near field for Wireless Power Transfer

Hi everyone
I want to ask, does the coupling between two antennas differ in the reactive and radiative near field regions.
Also I intend to ask that for reactive near field region, inductive coupling or magnetic resonant coupling by coils is better option than wireless power transfer by planar antennas (as planar antennas is most efficient gain wise in near field from what I have read).
If anyone can throw some light on this, it will be really helpful.

For a useful reference on electromagnetic coupling, maybe check out "Couplings of asynchronously tuned coupled microwave resonators" by J.S. Hong (or check out chapter 7 of his textbook, Microstrip Filters for RF / Microwave Applications). This definition of coupling is sometimes debated in terms of signs, but I believe its more or less accepted.

I have always assumed that the definition of the coupling coefficient translates well from near field to far field, but I've never dealt enough with antennas to investigate that myself.

As for your second question, typically inductive charging is what is meant by "near field" WPT, partly because it is a lot easier to create strong magnetic fields over a distance than electric fields. The problem with your question is "better option" changes a lot between applications. If you are designing a WPT system for electric vehicles, your definition of better is much different than someone designing for charging medical implants. If you could describe your design constraints a bit more (Tx/Rx size, gap, desired PTE, power levels, exposure, etc.), you can compare how different powering schemes affect you.

For example, far-field WPT is typically effective for low power levels, low PTE, large air gaps, and small Rx structures. Near field is effective for higher PTE, higher power levels, smaller distances, larger structures. But those are sort of just rules of thumb I work with, not hard distinctions.