Reducing coupling in compact arrays for WSN nodes via pre-fractal defected ground structures

Printed monopoles have shown good potential as small, wideband and efficient antenna solutions for sensor nodes. Their compatibility with standard printed circuit processes provides for straightforward implementation of compact arrays. Arrays can offer the advantage of diversity, which is a true enabler of mobile sensor networks. However, when building compact arrays with closely spaced elements, detuning occurs, along with loss of bandwidth, while mutual coupling hinders diversity. This work describes a simple yet efficient technique to reduce coupling and regain the bandwidth by inserting a defect on the ground plane of the device. Array performance was characterized numerically in terms of bandwidth, broadband radiation efficiency, mutual coupling, correlation coefficient and far-field pattern. Multi-decibel gains in mutual coupling reduction were noted.