Composite Right-/Left-Handed-Based, Compact, Low-Profile, and Multifunctional Antennas for 5G Applications

Two small multifunctional antennas based on the negative order resonance (NOR) are proposed for the 5G new radio (N78 band) application in this article. A novel ring-type resonator (RTR) inspired by the mushroom-type metamaterial structure is first proposed and studied by the equivalent circuit models and dispersion diagrams. The RTR comprises small patches to enhance the aperture efficiency and gain. By loading the left-handed (LH) components (gap capacitors and metallic vias), the first NOR (−1st NOR) mode is successfully excited, which leads to significant antenna size reduction. The designs overcome the bandwidth limitation of the conventional miniaturized antennas. A dual-polarized antenna with a compact size of
$0.30\lambda _{0} \times 0.30\lambda _{0} \times 0.04\lambda _{0}$
and a multifunctional antenna with a low profile of
$0.06\lambda _{0}$
are developed with a shared aperture configuration. Moreover, they achieve a good bandwidth that well covers the 3.3–3.8 GHz N78 band, a high radiation efficiency that is larger than 80%, and flexible multipolarized radiation. These features make them preferable candidates for microcells to meet the 5G communication demands.