| strength of coupling between coupled resonators which is defined as the ratio of coupled energy to stored energy and can be obtained from two split resonance frequencies by |
k = (fh2 – fl2) / (fh2 + fl2)
fh is the higher resonance frequency and
fl is the lower resonance frequency
Note 1 to entry: The coupling is mainly made either magnetically or electrically which is called magnetic or electric coupling, respectively.