Antenna design for a proximal soil moisture mapping sensor

We present the design of an antenna array for a proximal soil moisture sensor that will be mounted on an irrigator. The sensor maps the soil moisture of the ground ahead and uses the information to modulate the water volume of the irrigator. The design objective of the antenna is to enable the sensor to map the ground surface at less than 1m2 resolutions. Applying radar analysis, it is determined that the antenna needs to maintain a directivity performance of 12 dBi over a bandwidth of 500 MHz. An array of four log-periodic dipole antennas is designed, constructed and measured. Measurement showed that the array exhibit a flat gain performance of 10.3 dBi over the frequency range of 400-1200 MHz. The dimensions of the antenna array are 0.35m×0.45m×0.55m. Based on the measured parameters, we computed that the sensor is capable of achieving a ground resolution of 0.62m2.