Compact Dual-band Hybrid-Fractal MIMO System for UMTS and LTE Mobile Applications

This article presents a bandwidth enriched, dual-band, compact, multiple-input-multiple-output (MIMO) antenna with high isolation for UMTS and LTE applications. The proposed coplanar waveguide (CPW)fed, hybrid fractal MIMO antenna was created by integrating Koch fractal and Sierpinski fractal on a rectangular patch radiator. The MIMO antenna uses a rectangular shaped partial ground plane with a T-shaped stub on the ground plane to improve the isolation between radiators. The iterative technique, using the Koch curve and the Sierpinski square slot fractal was used on the rectangular patch to reduce the size of the MIMO antenna and retain the electrical performance. By using an amalgamated fractal configuration and a CPW feed, a large impedance bandwidth was achieved: 80% wide bandwidth over the operating frequency of 1.81-3.17 GHz with a compact size of 25 x35 mm(2). The prototype of the optimized MIMO configuration was fabricated using the FR4 substrate, and its characteristics were measured. The proposed antenna resonates at 2.1 and 2.6 GHz. The antenna parameters, including the reflection coefficient (S11, S12, S21, and S22), surface current distributions, realized gain and radiation patterns were simulated and measured. Additionally, the diversity performances of the MIMO antenna were analyzed in terms of diversity gain (DG) and envelope correlation coefficient (ECC). The proposed antenna retains high isolation of less than -20 dB from 1.81-3.17 GHz band; the DG and the ECC are greater than 9.5 dB and less than 0.08, respectively. The peak gains of the proposed antenna are 5.8 dBi and 6.9 dBi at 2.1 GHz and 2.6 GHz, respectively. Hence, the proposed hybrid fractal MIMO antenna is a good candidate for both UMTS and LTE applications.