With the advancement in subsurface communications technology, an overarching solution to a underground phased array antenna design for digital agriculture requires interdisciplinary research involving topics ranging from insights on the constitutive parameters of the soil medium and impact of soil moisture on the array factor to antenna measurements and subsurface communication system design. In this paper, based on the analysis of underground radio wave propagation in subsurface radio channel, a phased array antenna design is presented that uses water content information and beam steering mechanisms to improve efficiency and communication range of wireless underground communications. It is shown the subsurface beamforming using phased array antenna improves the wireless underground communications by using the array element optimization and soil-air interface refraction adjustment schemes. This design is useful for subsurface communication system where sophisticated sensors and software systems are used as data collection tools that measure, record, and manage spatial and temporal data in the field of digital agriculture
