Date of this Version
A. Salam, and M. C. Vuran, Smart Underground Antenna Arrays: A Soil Moisture Adaptive Beamforming Approach, Tech. Report No. TR-UNL-CSE-2017-0001: Department of Computer Science and Engineering, University of Nebraska-Lincoln, Jan 2017.
In this paper, a novel framework for underground beamforming using adaptive antenna arrays is presented. Based on the analysis of propagation in wireless underground channel, a theoretical model is developed which uses soil moisture information and feedback mechanism to improve performance wireless underground communications. Array element in soil has been analyzed empirically and impacts of soil type and soil moisture on return loss and resonant frequency are investigated. Beam patterns are investigated to communicate with both underground and above ground devices. Depending on the incident angle, refraction from soil-air interface has the adverse effects in the UG communications. It is shown that beam steering improves the UG2UG communications by providing the high gain lateral wave. It is also shown that angle which enhances lateral wave is a function dielectric properties of the soil which is affected by moist and texture of soil and it varies from 0 to 16 with soil moisture variations. It is shown that for low soil moisture content optimal UG lateral angle is high and it decreases with change in soil moisture. Planar array structures are considered and different optimization approach has been developed to improve the performance of soil moisture adaptive beamforming.