Loop Autenna For Underwater RF Communication

Underwater communication is widely used in the information exchanging between submerged devices and divers, navigation and controlling of autonomous underwater vehicle (AUV) and underwater wireless sensor networks technologies. With the continued expansion of functions, applications of transmission in sound and image information require the support of communications with high data rate. Current technology is severely restricted by the complex shallow water environment. Underwater acoustic technology has disadvantage of low transmission rate, long delay and narrow bandwidth, which caused by noise, interference and multipath effect. Underwater optical wireless communication is constrained by scattering, absorption and precision alignment requirements, which made it difficultly to meet the application requirements.Since the great transmission attenuation of electromagnetic wave in water, SLF and VLF is applied in practice, which have huge antenna, extreme high power and low data rate. In recent years, with the development of antenna researching and digital signal processing, high rate underwater communication is possible. Small and high performance antenna becomes an important research direction. Research has been carried out in antenna designing abroad, and has made some progress. This paper presents the work of the key issues in underwater communications, mainly researching on the designing and testing of the loop antenna.Firstly, the basic propagation theory of EM (electromagnetic) waves in free space and underwater is introduced. The advantage of using magnetic field in underwater communication is point out. The influence of surface wave is analyzed.The designing of loop antenna using in short range communication is carried out. Base on the analysis and simulation of dipole and magnetic loop, the loop antenna with advantages of small size, high magnetic emission energy and SNR is adopted. Key parameters and influencing factors of loop antenna are discussed and selected.After fabricating and debugging, the RF communication experimental system base on loop antenna was designed. Using QPSK modulation, the comprehensive performance of the antenna has been investigated on experimental trials. The experiment results show that the system's date rate can be up to 32kbps at 60m distance.