Radiowaves in the HF band (3-30 MHz) are reflected back to earth by the upper part of the atmosphere, so they can propagate over very long distances without the need of line of sight. If the departure angle respect to the horizon is low, the wave may reach up to 3000 km without the need of any repeater. However, if the departure angle is close to 90º, the incidence is near vertical and the wave may reach up to 300 Km without line of sight. This is known as Near Vertical Incidence Skywave (NVIS) communications.
The Remote IoT (RIoT) line is focused on the application of HF Communications in three situations: i) emergency situations where any other communication system crashes ii) sensors located in remote places iii) extend the concept of Internet of Things to devices located in places out of coverage of traditional systems. This activity can be divided into three parts:
NVIS communications: The physical layer can be optimized for two different goals: i) high speed systems for digital voice and messages, in order to communicate two isolated points due to either an emergency situation or remote villages in developing countries ii) low speed and low power systems with compact antennas, for solar or wind powered systems applied to remotes sensors, rescue of people or to extend the concept of Internet of Things to devices located in places out of coverage. The research will focus on new modulations with multiple antennas (MIMO and polarization diversity) for high speed, as well as modulations to be used with high efficiency amplifiers.
Compact antennas in the HF band: NVIS communications for sensors need small antennas. Although the optimal antenna for the HF band has to be very large (from 15 to 50 meters for a dipole in NVIS), it is possible to design much smaller antennas with moderate losses. Other kind of antennas techniques should be investigated such as those based on magnetic antennas or fractal-based geometries. The research will focus on the antenna miniaturization, the matching networks and the measurement of the electromagnetic performance (measurement of radiation patterns at HF is a challenge due to large distances to achieve far-field criteria in order to correctly measure radiation patterns) .
Non-conductive antennas for IoT: The antennas made of non-conductive materials may be transparent. This open up the doors of antennas built on solar panels and invisible antennas. The antennas built on solar panels have several advantages: i) zero-power sensors, as the energy for both the electronics and the antennas comes from the solar panel ii) low visual impact, as the antennas is built on the solar panel without requiring additional space. The research will focus on new radiating elements under different configurations (patch, slots, arrays), the level of transparency of the antennas and the interaction with the solar panel and the behaviour of other transparent solid dielectrics.
The group has a collaboration agreement with Fractus Antennas Corporation, which grants its facilities to measure antenna radiation patterns with its sophisticated SAtimo Stargate-32 anechoic chamber, as well as the close cooperation between the researchers of both institutions.