A 3-dB forward coupler using composite right/left-handed transmission lines with shared short stubs

A novel forward coupler using composite right/left- handed (CRLH) transmission lines with shared short stubs is presented. Stubs of the parallel CRLH transmission lines are connected each other to share common short circuits. In this coupler, forward coupling depends on only shunt inductances in the even and odd modes because the CRLH transmission lines are not coupled and have no mutual inductances and capacitances. Since the shared short stubs provide a large shunt- inductance difference between the even and odd modes, a small forward coupler with tight coupling can be realized. The proposed 3-dB forward coupler is simulated and experimentally demonstrated in the S-band. Its length is seventh part of a conventional right-handed forward coupler with the same coupling.