Sparse-array metasurface: design of a feeding network and optimisation

Metasurface (MTS) antennas are 2D structures composed of a thin dielectric slab on which periodic arrays of metal patches are disposed. Feeding pins are located inside of the substrate and generate surface waves (SWs) when supplied. These propagating surface waves (SWs) in the dielectric slab are being perturbed by the slow spatial variation in the shapes of the patches. The resulting perturbation generates leaky-wave radiation, which can be controlled by altering the size, shape, and orientation of the patches. In particular, this master thesis focuses on the 3D design and full-wave analysis of sparse-array MTS antennas. Such arrays are based on a common metasurface but feature wider beam spacing, offering an efficient alternative for beam scanning applications compared to traditional phased array antennas. This larger spacing reduces the density of electronic components, at the expense of a reduced field of view. This technology has the potential to offer innovative solutions to a wide range of applications, including air traffic control, satellite communications, and other fields. The primary objective of this master thesis is to design the feeding network of the sparse-array MTS antennas, which is responsible for supplying the feeding pins. The purpose of the feeding pins is to launch a planar surface wave that propagates along the MTS and excites the arrays of patches in a uniform manner. The feeding network aims therefore to achieve homogeneous currents in the aforementioned feeding pins, despite the very strong coupling between those pins. Firstly, a theoretical model of the feeding network is constructed, based on the principles of transmission line theory. The model is then subjected to a series of parametric tests and optimisations until the results are deemed satisfactory. Afterwards, a spectral analysis is conducted to ascertain the consistency of the propagating fields and the similarity between the radiation pattern generated by the MTS and the predicted one. We validated and improved the 2D simulations conducted in a previous study through 3D full-wave analysis, by comparing the radiation patterns obtained using a full-wave commercial solver and those simulated with a simpler in-house code. A satisfactory design has been found.