  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.
