Design and Development of Reconfigurable Antenna System for Precision Agriculture

Abstract

During the past few decades, the wireless research community has drawn extraordinary attention to wireless power transfer (WPT) because it can effectively extend the life of a power-limited system by wirelessly charging it. The thesis proposes a reconfigurable antenna system to provide WPT to randomly distributed agriculture sensors. The agriculture sensors can be humidity, temperature, or any other low-power sensors with energy harvesting abilities. The antenna system is consist of reconfigurable beamforming antenna array and a compact UHF semi-passive RFID tag. The beamforming array is mounted on a flying UAV and act as a transmitter antenna to wirelessly charge agriculture sensors. While the semi-passive RFID tag is part of agriculture sensors i.e., humidity and temperature sensors. In the first part, a compact, high-gain reconfigurable antenna array with 9 dBi of realized gain is designed that was deployed on a flying UAV. Whereas the second part is devoted to design of a UHF semi-passive RFID tag with maximum gain of 1.35 dBi with power scavenging capabilities for agriculture sensors. The RFID tag is used to send agriculture sensor’s mainly humidity sensor’s data along with its ID to the UHF RFID reader but taking the sensor’s data and sending it to the RFID reader is not the scope of the thesis topic. The thesis focuses on the implementation of antenna system for precision agriculture. The ISM band (2.45 GHz) is considered for the WPT to the agriculture sensors, whereas the UHF band (868 MHz) is considered for the RFID communication with the reader. To enable wireless powering capabilities in the sensing part (semi-passive RFID tag), they are loaded with a power scavenging circuit consists of a harvesting antenna, rectifier, and a power-management unit (PMU). The RF energy harvesting antenna captures the RF power at 2.45 GHz, rectifier convert the captured RF energy into usable DC and a PMU is utilized to store and deliver a regulated dc supply to the RFID tag IC for its operation in semi-passive mode that extends the RFID communication range from 2 to 5m. Before and after the cold start of PMU, a WPT range of 2.5 m and 7 m is achieved with transmitted power considerations of 20 dBm, GTX 9 dBi, and GRX 7dBi transmitting and receiving antenna gain correspondingly. In addition, advanced manufacturing techniques like as 3D printing are used to built 3D printed cases for beamforming transmitting array, RFID reader module and for agriculture sensor part i.e., a 3D printed case for energy harvesting circuit and RFID tag that may be buried under the soil to protect the RF components from corrosion.