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StatusOngoing
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Status date2025-01-28
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Activity Code7B.053
The demand for high data rate mobile communications has continuously increased in the last years and a massive expansion of mobile satellite terminal market into new domains is expected in the future. The beam steering antenna is the main cost item of a mobile satellite terminal. However, the established antenna beam steering architectures cannot meet all the demands of many new civil markets, such as low cost, low power consumption, and low profile. The objective of the proposed activity is to develop an innovative low-profile beam scanning antenna solution based on a totally mechanic mechanism and suitable for VSAT applications. The objective was to cover a percent band of 10%. Starting from a TRL 2, objective of this project was to reach a technological readiness level of 5, to proceed then to the industrialization and qualification phases. The proposed solution may find application in various market segments which require advanced and interactive services, like internet connection on-board high-speed trains, long range buses, ships and airplanes, and, in general, transmission and reception of real time audio-video information with high bidirectional data rate for public utility/rescue/recreational vehicles travelling in remote areas (e.g. telemedicine or security and emergency management).
The target of the project is to develop a beam-steering solution, which is based on mechanical scan where the volume of the antenna does not change; therefore, trivial 3D rotation of static antennas is not an option. The solution, based on flat Risley prisms, allows to have low-profile beam-scanning antennas, has the difficulty of controlling the grating lobes generated by the period pattern of the flat Metascreens, and this is the key challenge that had to be tackled.
Conventional mechanically scanning reflectors are too heavy, bulky and fragile for this application. Multi-panel antennas represent a hybrid solution that alleviates the problem of losses and allows for an important thickness reduction, but they might suffer from panel shadowing and/or pattern degradation for low elevation angles. The solution proposed in this activity has the great advantage of exploiting the low-power required to repoint the antenna, typical of mechanical systems, without the mechanical complexity of scanning reflectors, and also the low profile which is generally a feature of electronically-scanning antennas. Several groups have been working on similar techniques, but the solution developed in the MUST project has great performance in terms of grating lobes with respect to existing solutions.
Despite having separate apertures for RX and TX, due to the large frequency separations between the two bands, the MUST terminal has dual switching circular polarization capability without using external polarizers. Furthermore, if compared to existing solutions based on rotating discs, this technology does not employ rotary joints since the main antenna does not need to move and is designed to produce a static broadside beam, whereas the reconfigurability is introduced by the rotating Metascreens. Finally, the fabricated prototype has shown scanning capabilities up to 65° from the broadside direction, and additional tests showed that this value can be even enlarged by additional 5-10°. It is important to note that, given the technique used to implement the Metascreens, the cross-polar discrimination has always optimal values throughout the entire scan range, unlike conventional flat scanning antennas.
The selected architecture is based on two separate apertures (one for TX, one for RX, at Ka-band). Each aperture is composed of a primary radiator topped by two rotating metasurface-based screens (sometimes referred to as either Metalenses or Metascreens) which are free to rotate independently. The primary radiators are low-profile reflectors which have been custom designed using in-house proprietary codes. One peculiarity of the two reflectors (for TX and RX) is that they have the same reflector shape, while only the feed (which is field-mountable) is different. The two metascreens of each aperture are identical, and they exploit the Pancharatnam-Berry phase effect in order to provide the desired beam tilting. This allows to obtain the beam scanning effect which according to the Risley prisms, which in this case are implemented in a low-profile configuration with controlled levels of the grating lobes. Each antenna has also dual switching circular polarization capabilities, in order to adapt to work at different geographical locations.
The project plan included the investigation of two alternative solutions to be implemented. After the preliminary design phase and the critical design phase, the solution based on rotating Metascreens has been selected as baseline solution. Next, the full terminal has been designed, manufactured and tested. The tests have shown the capability of the terminal to receive a signal from a GEO satellite (Eutelsat KA-SAT) for different attitudes of the terminal (rotation along its three axes).
The project has reached its termination, after the outdoor tests that showed the possibility for the terminal to receive the signal from a GEO satellite, after repointing the beam due to the attitude change in the terminal orientation.
