A MINIATURIZED TRIPLE-BAND BRANCH-LINE COUPLER BASED ON SIMPLIFIED DUAL-COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINE

Abstract

A miniaturized triple-band branch-line coupler based on the simplifled 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 frequency points with phase of i90-degree in the passbands; this characteristic can be used to design triple-band quadrature microwave components. The proposed branch-line coupler is fabricated and measured, the measured and simulated results are in good agreement with each other, showing that the triple-band operating at 3.06GHz, 4.00GHz and 5.54GHz, the useful bandwidths are 2.97GHz{3.16GHz, 3.82GHz{4.12GHz and 5.48GHz{5.67GHz. In addition, compared with the conventional branch-line coupler, the whole size of the proposed one is 17mm£14:4mm (0:173‚£0:147‚) (‚ 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 efiective in the situation, which is sensitive to phase-changing, as the sign of phase difierence in the two outputs at the three frequency points keeps the same.