A miniaturized triple-band branch-line coupler based on simplified dual-composite right/left-handed transmission line

A miniaturized triple-band branch-line coupler based on the simplified dual-composite right/left-handed transmission line (S-D-CRLH-TL) is proposed in this paper. The electromagnetic characteristics of S-D-CRLH-TL are analyzed by the simulator and equivalent circuit model, and the results prove that there are three frequencies with phase of -90° in the passbands; this characteristic can be applied in designing triple s are in good agreement with each other, showing that the triple-band operating at 3.06 GHz, 4.00 GHz and 5.54 GHz, the useful bandwidths are 2.97 GHz-3.16 GHz, 3.82 GHz-4.12 GHz and 5.48 GHz-5.67 GHz. In addition, compared with the conventional branch-line coupler, the whole size of the proposed one is 17 mm × 14.4 mm (0.173λ × 0.147λ) (λ is the wavelength in low frequency), it realizes a 73% size reduction. Moreover, compared with the triple-band branch-line coupler based on the double-Lorentz transmission line metamaterial, the proposed branch-line coupler is more effective in the situation, which is sensitive to phase-changing, as the sign of phase difference in the two outputs at the three frequency points keeps the same. © 2010 EMW Publishing. All Rights Reserved.