Beamfocusing Capabilities of a Uniform Linear Antenna Array in the Holographic Regime
The use of multiantenna technologies in the near field offers the possibility of focusing the energy in spatial regions rather than just in angle. The objective of this paper is to provide a formal framework that allows to establish the region in space where this effect can take place and how effici...
| Autores: | , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Centre Tecnològic de Telecomunicacions de Catalunya (CTTC) |
| Repositorio: | r-CTTC. Repositorio Institucional Producción Científica del Centre Tecnològic de Telecomunicacions de Catalunya (CTTC) |
| OAI Identifier: | oai:cttc.fundanetsuite.com:p8873 |
| Acceso en línea: | https://cttc.fundanetsuite.com/Publicaciones/ProdCientif/PublicacionFrw.aspx?id=8873 |
| Access Level: | acceso abierto |
| Palabra clave: | Receivers Channel models Signal to noise ratio Antenna arrays Spatial filters Array signal processing Electromagnetic scattering Mathematical models Focusing Ellipsoids Holographic arrays near-field communications beamfocusing extra large antenna arrays |
| Sumario: | The use of multiantenna technologies in the near field offers the possibility of focusing the energy in spatial regions rather than just in angle. The objective of this paper is to provide a formal framework that allows to establish the region in space where this effect can take place and how efficient this focusing can be, assuming that the transmit architecture is a uniform linear array (ULA). A dyadic Green's channel model is adopted, and the amplitude differences between the receiver and each transmit antenna are effectively incorporated into the model. By considering a second-order expansion of the signal to noise ratio (SNR) around the intended receiver, a formal criterion is derived in order to establish whether beamfocusing is feasible or not. For the regions where beamfocusing is indeed possible, an analytic description is provided that determines the shape and position of the asymptotic ellipsoid where a minimum SNR is achieved. Further insights are provided by considering the holographic regime, whereby the number of elements of the ULA increase without bound while the distance between adjacent elements converges to zero. This asymptotic framework allows to simplify the analytical form of the beamfocusing feasibility region, which in turn provides some further insights into the shape of the coverage regions depending on the position of the intended receiver. Furthermore, a closed form analytical expression is provided for the coverage ellipsoids, which allows to design practical beamfocusing codebooks for a given array length. These results prove that beamfocusing is only feasible when the receiver is located between a minimum and a maximum distance from the array, where these upper and lower distance limits effectively depend on the angle of elevation. In particular, it is shown that beamfocusing is only possible if the size of the ULA is at least $4.46\lambda$ where $\lambda$ is the transmission wavelength. |
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