A Novel Highly Directional Antenna Array Based on Epsilon-Mu-Near-Zero (EMNZ) With Air-Gap Structure

In this article, we initially construct an equivalent epsilon-near-zero (ENZ) medium by utilizing an air-filled waveguide operating at its cutoff frequency. Following this, based on the principle of dielectric doping, we doped the metal medium into the ENZ waveguide cavity to realize a waveguide epsilon-mu-near-zero (EMNZ) medium. To apply it to antenna design, an array of slots is transversely etched along the sidewall of the EMNZ waveguide to radiate electromagnetic (EM) wave outwards, thereby constructing an equal spacing ten-element antenna array featuring a simplified feeding network and impedance matching, with simulation confirmed the antenna’s strong directivity. We have optimized the element spacing using a genetic algorithm, achieving a low reflection coefficient while concentrating the elements in the main lobe direction, which has successfully decreased the sidelobe level (SLL) to −22.01 dB and enhanced the peak gain to 14.01 dBi. As measured, the optimized equal spacing antenna array operates at the frequency point of 4.986 GHz (−10-dB impedance bandwidth less than 0.1%), but it achieves a radiation efficiency of 90.8% within a length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\lambda $ </tex-math></inline-formula> and a strong directivity, making it applicable to fields such as radar detection and satellite communication. Moreover, we explored the 2-D form and the deformability of the EMNZ antenna array, achieving a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\times 10$ </tex-math></inline-formula> planar antenna array with a gain of 21.3 dBi and a folded antenna array with an extremely low SLL of −35.7 dB, further expanding its application prospects.