An SRR-Loaded Compact Triple-band 4-Element MIMO Design for WLAN/WiMAX/C-band Applications

A planar compact triple-band quad-element MIMO design with polarization diversity is proposed in this work for WLAN (2.4 GHz), WiMAX (3.5 GHz), and C-band applications. The MIMO antenna element with a compact size (
$15\times 24\ \text{mm}^{2}$
) comprises of Split-Ring Resonator (SRR) loaded open square-loop monopole (OSLM). Four such antenna elements are placed at the corners of an FR-4 substrate of dimensions
$53\times 53\ \text{mm}^{2}$
with an orthogonal orientation of adjacent elements to implement quad-element MIMO geometry. By offsetting the elements' position and reducing the substrate area of
$L_{off}\times W_{off}$
at each corner, cost and footprint are reduced. The proposed MIMO design is resonating at 2.44, 3.5, and 4.4 GHz and accomplishes an −10 dB return loss bandwidths of 85 MHz (2.4 – 2.485 GHz), 260 MHz (3.36 – 3.62 GHz), and 850 MHz (4.1 – 4.95 GHz) in the lower, middle and higher working bands. Despite its compact size, it reports good minimum isolation of 15.6 dB across all three bands. It provides stable omnidirectional radiation characteristics in all the operating bands. The diversity performance is verified with its envelope correlation coefficient (ECC) and Diversity Gain (DG) metrics. The proposed MIMO geometry can be a good candidate for portable wireless devices due to its compact feature with good radiation/diversity performance.