The hybrid coupler, or 3 dB directional coupler, in which the two outputs are of equal amplitude takes many forms.
Not too long ago the quadrature (90 degree) 3 dB coupler with outputs 90 degrees out of phase was what came to mind
when a hybrid coupler was mentioned. Now any matched 4-port with isolated arms and equal power division is called a
hybrid or hybrid coupler. Today the characterizing feature is the phase difference of the outputs. If 90 degrees, it is a 90
degree hybrid. If 180 degrees, it is a 180 degree hybrid. Even the Wilkinson power divider which has 0 degrees phase
difference is actually a hybrid although the fourth arm is normally imbedded.