The coupler features wide range of realizable frequency ratio, multiple flexible selections of open- or short-circuited and pi- or T-network topologies.

Figure 7 presents the desired dual-band branch-line and another one of implementing T-network circuit structures, composed by two identical sections of a transmission line ([Z.sub.TA], [[theta].sub.TA]) and a shunt reactive elements (j[Y.sub.T]).

Since the T-network also substitutes the desired dual-band branch-line, by the same analytical method as in Section 3, the circuit parameters can be derived as follows