A cavity-backed slot antenna with high upper hemisphere efficiency for sewer sensor network

A wireless sewer sensor network has been widespread to monitor combined sewer overflow (CSO) causing human health and environmental hazards. To enable the wireless interconnection between sensor nodes, a radiator needs to be embedded into a manhole cover with sufficient mechanical strength. In addition, the high efficiency in upper hemisphere is essential for successful communication to above-ground sensor nodes. In order to meet these requirements, a full wavelength slot antenna embedded in a shallow cavity inside a cast-iron manhole cover is designed. An electromagnetic analysis is conducted to verify the antenna design. Simulation and measurement show a good agreement. The result shows 2.5dB higher total radiated power in three-dimensional upper hemisphere, compared to a half wavelength slot on the same substrate without a cavity.