Directional emission of a three-dimensional connection-type metamaterial.

Directional emission of electromagnetic waves plays an essential role in laser radar and free-space communication. For most directional antennas, bandwidth and miniaturization are a pair of contradictions due to their underlying interference mechanism. Connection-type metamaterials exhibit exotic electromagnetic response near zero-frequency, which relies on the global topology of mesh connectivity rather than resonance and thus has a broad working bandwidth. In this Letter, we investigate the broadband orientation-dependent coupling effect of a 3D double mesh metamaterial. Based on this effect, we achieve a broadband directional emission (relative bandwidth of 37.72%) using a compact structure (compared to twice working wavelength). Our work provides a novel, to the best of our knowledge, scheme to manipulate a long-wavelength wave and may pave the way to a miniaturized directional antenna.