An EEP-based robust beamforming approach for superdirective antenna arrays and experimental validations

TL;DR

This paper introduces an EEP-based superdirective beamforming method that accounts for mutual coupling, and proposes a robust algorithm to mitigate excitation errors, validated through simulations and real-world experiments.

Contribution

It presents a novel EEP-based superdirective beamforming approach with a closed-form solution and a robust optimization algorithm for practical antenna array applications.

Findings

Validated through full-wave simulations

Demonstrated superdirectivity in a prototype array

Showed robustness to excitation errors

Abstract

A superdirective antenna array has the potential to achieve an array gain proportional to the square of the number of antennas, making it of great value for future wireless communications. However, designing the superdirective beamformer while considering the complicated mutual-coupling effect is a practical challenge. Moreover, the superdirective antenna array is highly sensitive to excitation errors, especially when the number of antennas is large or the antenna spacing is very small, necessitating demanding and precise control over excitations. To address these problems, we first propose a novel superdirective beamforming approach based on the embedded element pattern (EEP), which contains the coupling information. The closed-form solution to the beamforming vector and the corresponding directivity factor are derived. This method relies on the beam coupling factors (BCFs) between the antennas, which are provided in closed form. To address the high sensitivity problem, we formulate a constrained optimization problem and propose an EEP-aided orthogonal complement-based robust beamforming (EEP-OCRB) algorithm. Full-wave simulation results validate our proposed methods. Finally, we build a prototype of a 5-dipole superdirective antenna array and conduct real-world experiments. The measurement results demonstrate the realization of the superdirectivity with our EEP-based method, as well as the robustness of the proposed EEP-OCRB algorithm to excitation errors.