Abstract
For ubiquitous sensor network applications in shallow water coastal zone, a low-cost consumer L1 C/A-code GPS receiver with a small patch antenna is a suitable sensor for positioning and timing of a node. The goal of this research is to realize a single-frequency RTK-GPS sensor providing precise positioning information in order to improve the underwater ultrasonic communication between sea surface and bottom floor in shallow water, where many multipath echos and non-uniform water flows degrade the communication quality. Since antenna gain pattern is one of the important factors for RTK-GPS, we focused on the optimization of GPS antennas implementation, such as ground plane size and antenna height above sea surface. In this paper, several different combinations of the groud plane and antenna height were evaluated by field tests. The antenna gain paterns including sear-surface effects were also evaluated by an electromagnetic field analysys method called UTD. The results showed that certain combination of ground plane and antenna height provides favorable signal reception condition above sea surface and improves the fix-rate of signle-frequency RTK-GPS positioning.
