Abstract
Wireless sensors emerged as narrowband, resource-constrained devices to provide monitoring services over a wide life span. Future applications of sensor networks are multimedia-driven and include sensor mobility. Thus, sensors 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. An efficient technique to reduce coupling in compact arrays is described herein: a defect was inserted in the ground plane (GNDP) area between each pair of elements. The defect disturbed the GNDP currents and offered multidecibel coupling suppression, bandwidth recovery, and reduction of in-band correlation. Minimal pattern distortion was estimated. Computational results were supported by measurements. The bandwidth of unloaded arrays degraded gracefully from 38% to 28% with decreasing interelement distance (0.25 to 0.10). Defect-loaded arrays exhibited active impedance bandwidths 37–45%, respectively. Measured coupling was reduced by 15–20 dB.
Highlights
It has been fifteen years since wireless sensor network (WSN) pioneers first envisioned the cubic-millimeter “Smart Dust” sensor node [1, 2]
In case of severe correlation, a simple yet efficient technique to reduce the coupling is proposed: the return currents on the GND plane are disturbed by a nonperiodic photonic bandgap (PBG) structure known as the defected ground structure (DGS)
D = 30 mm d = 27 mm d = 24 mm d = 21 mm d = 18 mm d = 15 mm d = 12 mm PCB width varied with interelement distance d as in (3): subWarray where subWi=3 = 18 mm
Summary
It has been fifteen years since wireless sensor network (WSN) pioneers first envisioned the cubic-millimeter “Smart Dust” sensor node (or “mote”) [1, 2]. In case of severe correlation, a simple yet efficient technique to reduce the coupling is proposed: the return currents on the GND plane are disturbed by a nonperiodic photonic bandgap (PBG) structure known as the defected ground structure (DGS). This effort is a straightforward and cost-effective step towards the fabrication of square-inch diversity antenna arrays for sensor networks. Improvement of both types of efficiency implies that this method offers mutual coupling reduction and bandwidth recovery.
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