Pattern-Reconfigurable Unidirectional Dipole Antenna Array Fed by SIW Coupler for Millimeter Wave Application

A directional two-element mm-wave dipole antenna array with reconfigurable patterns is presented in this paper. An substrate integrated waveguide (SIW) 90° coupler is used to realize reconfigurable patterns of the antenna array. The two dipole elements are parallel in space, and there is a distance of <inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula>/4 (<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength of the free space) between them. When the two inputs of the 90° coupler are excited, respectively, two completely opposite radiation patterns are able to be achieved. In order to further enhance the directivity of the proposed antenna, two groups of novel zero-index metamaterials and three metallic strips are introduced. As a consequence, a 0.7–1.2 dBi gain enhancement and reduced back lobe are obtained within the working frequencies. The measured amplitudes of S₁₁ and S₂₂ are below −10 dB from 45.5 to 49.5 GHz, and the measured gain is all great than 5 dBi within this band.