Performance enhancement of directional coupler using split ring resonator

In this paper, a technique to enhance the performance of directional coupler is proposed by incorporating the structure of split ring resonator (SRR). The directional coupler which is conventionally design on a grounded dielectric substrate is reconstructed by inserting the structure of SRR between the microstrip lines and the groundplane. This construction is expected to improve the performance of directional coupler, i.e. reflectivity and transmitivity. The number of SRR incorporated in the structure is limited into 9 per line due to the available space of directional coupler. The proposed directional coupler with SRR is then deployed on 2 stacked layers of FR4 Epoxy dielectric substrate with total thickness of 1.6mm and the dimension of 130mm 53mm. Prior to the hardware realization, the geometry of SRR is investigated numerically to obtain the optimum performance of directional coupler. From the results, it shows that the measured results of reflectivity (11) and transmissivity (21) are comparable to the simulated results. The 11 value for each port is less than -20dB, while the 21 value is closed to -20dB. However, at some frequency ranges the measured results show the reflectivity less than -10dB and the transmissivity is more than -5dB.