Isolation Enhancement for Vivaldi Antennas Using Hyperbolic Metasurface

In this communication, we propose a block-and-guide method of enhancing isolation between Vivaldi antennas in the whole X-band using hyperbolic metasurface (HMS). The HMS consists of periodic parallel metallic strips patterned on a thin dielectric substrate. Due to its strong anisotropy, the HMS exhibits a passband for electromagnetic (EM) waves propagating along the strip direction while a stopband for EM waves propagating along the orthogonal direction. When the HMS is placed close to the opening end of the Vivaldi antenna, the broadside radiation of the antenna can be suppressed while the endfire radiation is almost unaffected, leading to enhanced isolation between adjacent antennas. Rather than adding auxiliaries in between antennas, the HMS can be readily integrated into the antenna radiator structure, which is more favorable for practical applications, especially in compact spaces. To verify this method, the prototype was fabricated and measured. Both simulated and measured results show that when the distance is <inline-formula> <tex-math notation="LaTeX">$0.5\lambda _{0}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength of 10.0 GHz) between two Vivaldi antenna elements, the isolation can be increased by at least 10.0 dB in the whole X-band. This work provides an alternative to enhance isolation between wideband endfire antennas and may find applications in radar, wireless communication, and so on.