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Low-Cost Metasurface Leaky-Wave Antenna for Mobile Satellite Communications

Periodic Reporting for period 1 - MELASAT (Low-Cost Metasurface Leaky-Wave Antenna for Mobile Satellite Communications)

Reporting period: 2016-05-03 to 2017-05-02

Nowadays, having an inexpensive broadband internet connection no matter where you are is an increasing social demand. In order to have internet access independently on the user’s location, satellite communication is the best solution, since it does not rely on available infrastructure. In this way, by means of a terminal that can communicate continuously with a satellite, users could benefit from a fast data connection anywhere in the world, even when traveling in an airplane, a ship or train. Additionally, a low-cost technology for broadband satellite connectivity could be a viable solution to provide poor countries and isolated areas with broadband internet without strong investments.

Commercial solutions for ground terminals are based on parabolic reflector antennas with mechanical steering. Although they are cost-effective solutions, they require frequent maintenance and are significantly bulky. For low-profile antennas, phased arrays that perform electronic steering can be an appealing alternative, since they can be printed in planar technology and are fast changing the pointing angle. However, they have a corporative feeding network and, additionally, in order to get high gain, the array must contain a significant number of elements and phase shifters, thus leading to expensive and complex structures.

The project investigates a novel low-cost antenna solution for broadband satellite connectivity, so that inexpensive broadband internet connection can be provided without need of deployed infrastructure. With such a technology, the satellite industry could provide enhanced connectivity that would open vast new markets at an unprecedented scale.

More specifically, the project goal is the development of an antenna technology that has the advantages of printed technology (light weight and low profile) but reduces costs and complexity of phased arrays. This technology entails a real challenge and an important market niche that this project is trying to cover. As solution, we propose the combined use of metasurfaces with leaky-wave antennas (LWAs) to meet the challenging requirements for broadband mobile satellite communications (broadband beam steering with high gain) at lower costs and complexity than the state-of-the-art solutions. The proposal consists specifically of a low complexity electronically steered LWA with a metasurface on top to provide the needed gain and scan angle range.
The main objective of the project is to develop a low-cost antenna technology for mobile satellite communications based on the use of Huygens' metasurfaces in leaky-wave antennas (LWAs). The principal challenge to accomplish the main goal was the investigation of novel concepts related to the innovative combination of LWAs and metasurfaces. In this first period, the new antenna concept has been already developed, combining for the first time bianisotropic Huygens' metasurfaces with LWAs; and the choice of the metasurface and LWA geometries have been also made during this period. Particularly, the developed concept is a parallel-plate waveguide in which the top plate is replaced by a bianisotropic Huygens' metasurface. This concept has demonstrated significant potential, since it allows arbitrary field transformation from the field inside the waveguide and important flexibility in the radiation parameters. The theoretical derivation of this novel concept has been developed, leading to closed-form expressions for the design. Therefore, this novel technology (not explored before) is supported by a solid theoretical derivation and, therefore, a great part of the main objective has been achieved.

Specifically, the sub-objectives for the first year were the bibliographic study about Huygens' metasurfaces, the development of the novel antenna concept, the training in the electromagnetic simulator for these structures and a pre-design of the structure based on the theoretical methodology and simulation results. All these goals have been successfully accomplished. Several designs proving the mentioned flexibility of the radiation parameters (control of the pointing direction, the leakage factor, the waveguide height, etc.) have been carried out and corroborated by simulation results (presented at the European Conference on Antennas and Propagation, Paris, March 2017).

Work is being carried out on getting a final design to prove the concept without reconfigurability. The physical final implementation of the metasurface is a challenging part, since undesired effects must be solved. In order to make progress with the first prototype, we already acquired the required substrates and designed and fabricated the metallic structure that will form the leaky-wave antenna and support the metasurface. The final metasurface design is still under optimization.
Bianisotropic Huygens' metasurfaces are a recently-proposed concept that provides arbitrary electromagnetic field transformation with a surface made of passive and lossless particles. This novel concept has not been previously applied to the design of a leaky-wave antenna (LWA). Therefore, the concept developed in this project is a contribution to the state of the art of planar antennas and application of the metasurfaces. The advantage of the use of such a metasurface to build a LWA is the resulting powerful flexibility of the radiation parameters, and then, of the radiation pattern, with a low-profile and cost-effective technology. This progress paves the way to the development of a very competitive technology that significantly decreases the costs and complexity of current ground antenna solutions for mobile satellite communications.

The contribution presented at the European Conference on Antennas and Propagation was selected as finalist for the Best Paper Award in Electromagnetics and Antenna Theory.
General antenna solution concept.