Performance enhancement of coupled microstrip lines using split ring resonators

A novel technique to enhance the performance of coupled microstrip lines (CML) is proposed by incorporating the structure of split ring resonators (SRR). The structure of CML which is conventionally designed on a grounded dielectric substrate is reconstructed by inserting the structure of SRR between the lines and the groundplane. This construction is expected to improve the performance of CML, i.e. reflectivity, transmittivity, and cross-talks. The number of SRR incorporated in the structure is limited into 4 pieces per line due to the available of space. The proposed structure of CML with SRR is then deployed on 2 stacked layers of FR4 Epoxy dielectric substrate with the total thickness of 1.6mm and the dimension of 36mm × 80mm. Prior to the hardware realization, the geometry of SRR is investigated numerically to obtain the optimum performance of coupled microstrip lines. From the results, it shows that the measured results for S_nn and S_nm are comparable to the numerical ones obtained from simulations. The reflectivity, S_nn, for each port is less than -20dB, while the transmittivity, S_nm, is closed to OdB. The measured results also show that the near- and far-cross-talks are -30dB and -35dB, respectively.