Adaptive composite antennas for a city-wide sensor network

A city-wide wireless sewer sensor system becomes ´intelligent´ by having adaptive manhole cover antennas. Hundred and fifty wireless sensor nodes have been developed and deployed to monitor the sewer flow and to reduce the frequency of the combined sewer overflow (CSO) during heavy storm runoff in a mid-sized city: South Bend, Indiana in the US. The challenge for the wireless designer is to design a radiator that operates below ground as well as to improve the communication performance of the wireless sensor system. In this study, the authors replace a conventional cast-iron manhole cover with a composite manhole cover to create a radiator which is not only mechanically strong but electrically functional. The electrical characteristics of the composite are analysed by finding the relative permittivity and loss tangent. In addition, the effect of adaptive antennas is demonstrated to be extremely useful in terms of the packet reception rate and received signal strength. Measured results indicate that angular diversity significantly enhances received signal strength and the packet reception rate in the presence of interferers. The slot diversity antenna designed herein increased packet reception rate by 52.8% in the fielded system, compared to a uniformly radiating dipole antenna in the azimuthal plane.