Metamaterial based compact branch-line coupler with enhanced bandwidth for use in 5G applications

Abstract

A novel compact 5G branch-line coupler (BLC) based on open-circuit coupled-lines and interdigital capacitor structure is presented in this paper. The proposed BLC shows the composite right/left handed (CRLH) metamaterial transmission-line (TL) operation. The proposed BLC is designed and simulated using CST microwave studio. The designed BLC is then fabricated using the FR4 substrate (εr = 4.3 and h = 1.66mm). The proposed 5G BLC with coupled-lines and the interdigital capacitor has achieved the fractional bandwidth of ~ 40.2% and the size reduction of 54% as compared to the conventional BLC. The fabricated BLC operates at 2.74 - 4.15GHz frequency band with a coupling factor of -3 ± 0.2dB and the phase difference of 88o between the output ports. The BLC measurements are performed at the operating frequency of 3.5GHz. The simulated and measured scattering parameters and phase difference results are in good agreement with each other. The proposed design is suitable for use in future butler-matrix based beamforming networks for antenna array systems in 5G wireless applications.