Microwave soil moisture sensor based on phase shift detection of transmission coefficient in band-stop structures

In this paper novel miniature microwave soil moisture sensors based on band-stop structures have been developed, which operate at a fixed single microwave frequency. Sensors were designed in microstrip technology for use in wireless sensor networks for measurement and mapping of soil moisture in arable lands. Sensors detect transmission coefficient phase delay which is a function of the soil permittivity that is in turn in direct relation with soil moisture. Two novel sensors are proposed which operate at 2.54 GHz and 2.75 GHz. Both solutions offer two times wider ranges of the phase delay and from three to almost thirteen times greater sensitivities compared to conventional microstrip sensor solutions.