Tight or Loose Coupling in Directional Couplers

[moreho]

Hi my Friends

what means Tight or Loose Coupling in Directional Couplers?
is it try to clarify the Nominal Coupling Factor (ie. 3 to 20 dB as Tight and above 20dB as Loose)
or it try to clarify the Frequency Sensitivity (Ripple) in the Bandwidth?

Thanks in Advance

 

[reidintransit]

It is referring to the nominal coupling factor, but is not a precise term i.e. no hard line at 20dB.

 

[Hamid.Kiumarsi]

Tight and loose couplings refer to the value of the coupling level between coupled ports or coupled lines.
For example if you want to design a tandem coupler you need two pairs of coupled lines with coupling level of -8.34 dB. Then -6 dB is tighter and -10 dB is looser than -8.34 dB.