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In this letter, we propose the design of multibeam antennas with customized elevation angles based on near-field magnetic field coupling of metamaterials. The antenna consists of a monopole feed and four identical metamaterial transmission-line (MTL) structures surrounding the feed. The MTL structure is composed of two pairs of broadside-coupled omega rings (BCORs) that are connected by two straight strip-lines. Under such a framework, magnetic fields within the near-field zone of the monopole feed can be coupled efficiently by the inner BCOR, converted to travelling waves along the double strip-lines, guided toward the outer end of the MTL structure, and radiated by the outer BCOR like a loop antenna. Due to travelling wave nature of the MTL structure, there is phase lag along the MTL structure and the radiation main lobes are tilted towards the outward direction. By arranging several MTL structures around the feed monopole, multi-beam directional radiation can be realized. More interestingly, by adjusting structural parameters and pitch angles of the MTL structures, elevation angle of the radiation main lobes can be customized. To validate the design, we simulated, fabricated and measured four prototypes with pitch angles 0°, 15°, 30° and 45°. Both the simulated and measured results verify the design and show that multiple-beam radiation with customized elevation angle can be obtained. This work provides an alternative method of designing multi-beam antennas and may find applications in communication, surveillance, etc.

In this article, we propose a method of achieving broadband decoupling between large antenna arrays using magnetic metasurface (MM). To realize broadband isolation performance, the MM consists of four sub-regions composed periodic arrays of split-ring resonators (SRRs). The four sub-regions can achieve negative permeability in sequential frequency ranges, which can together cover the whole X-band by proper combinations. When the MM is placed between the antenna arrays, the propagation of the coupled electromagnetic waves will be suppressed due to the negative permeability, so the isolation between the antenna arrays will be enhanced. For simplicity, the broadband decoupling performance of MM is verified by using patch antenna elements. Prototypes were fabricated and measured. Both simulated and measured results show that when the distance between the two antenna elements is about half a meter, the isolation can be enhanced by at least 25.0 dB in the whole X-band, which convincingly verifies our method. This work provides an alternative to enhancing isolation between broadband antenna arrays and may find applications in electromagnetic compatibility of integrated masts, base stations, and so on.

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