Novel dual-band hybrid coupler using improved simplified CRLH transmission line stubs

In this paper, a novel dual-band hybrid coupler is designed by adopting improved simplified composite right-/left-handed (ISCRLH) transmission line (TL) stubs. An ISCRLH TL stub is composed of two ISCRLH TL unit cells with input and output uniform TL sections at the terminals, which can produce specified impedance and phase shift at two (arbitrary) different frequencies. The conditions for synthesizing the dual-band ISCRLH TL stub are discussed in detail, and then such a stub is applied to implement a novel dual-band hybrid coupler in microstrip configuration, simulated results of which reveal good performance and dual-band operation. The novel device is small, fully planar, and easily designed and fabricated.