Coupling and correlation reduction in compact arrays with embedded ground defects: Experimental verification

Future applications of wireless sensor networks (WSN) are multimedia-driven and include sensor mobility. Thus, sensor nodes must combine small size, large bandwidth, and diversity capabilities. Compact arrays, offering transmit/receive diversity, suffer from strong mutual coupling (MC), which causes lower antenna efficiency, loss of bandwidth, and signal correlation. The experimental results of an efficient technique to reduce coupling in compact arrays are described herein. A single defect was inserted in the ground plane (GNDP) area between each pair of elements, and disturbed the GNDP currents so as to offer multi-decibel coupling suppression, bandwidth recovery, and reduction of in-band correlation. The bandwidth of non-defected arrays degraded gracefully from 38% to 28% with decreasing interelement distance (0.25λ to 0.10λ). Defect-loaded arrays exhibited active impedance bandwidths 37–45% respectively. Measured MC was reduced by 15–20 dB. Finally, the paper also discusses the extension of this method to quasi-periodic defects.