Projeto de Up-Down Converter e Antena para Comunicações Wi-Fi Sub-Aquáticas

Abstract

Radio-waves are strongly attenuated in an underwater environment. However, as the attenuation increases with frequency, the use of lower frequencies may allow to obtain higher range communications. The possibility to use commercial Wi-Fi cards is extremely attractive due to the low cost and due to its large compatibility with IP protocol, allowing the use of Internet in underwater environment. There are several scenarios of application, among which stand out the environmental monitoring and aquaculture surveillance, sea ports as well as the oil, gas and raw materials industry. The work proposal concerns the development of an up-down converter system and an antenna that will allow the use of commercial Wi-Fi cards to establish an underwater communication with higher ranges. The developed system will downconvert the RF signal from the Wi-Fi card ($\sim$ 2.4GHz) to an IF frequency of around 100MHz. This signal will be the one that propagates through the underwater medium. On the receiver side, this signal will be upconverted to the Wi-Fi band again and the communication is established in this way. The circuit design uses an oscillator/PLL, a mixer, and it has amplification chain in the transmission and reception with automatic switching. The project includes the specification and design of the PCB and the antenna as well as the obtained results in measurements performed in a real field.