A DETACHED ZERO INDEX METAMATERIAL LENS FOR ANTENNA GAIN ENHANCEMENT

In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modified split ring resonators (MSRRs) is proposed for antenna gain enhancement. The effective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an effective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary reflectors in enhancing antenna gain, which is quite different from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly affect the gain enhancement, which further confirms that the ZIML can be detached from antennas. Simulated results show that the effective refractive index of the detached ZIML is near zero in a broad frequency range where the effective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One finds that evident gain enhancement is obtained from 8.9 GHz to 10.8 GHz and the greatest gain enhancement reaches up to 4.02 dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4 GHz and 5.8 GHz, respectively.