Design of a High-Rejection Filtering Antenna Based on Nonuniform Metasurface

This paper presents a high-rejection filtering antenna based on nonuniform metasurface (MTS). The antenna consists of three metal layers and two substrate layers. The upper metal layer is nonperiodic MTS patches with removed units. The MTS is fed by a T-shaped microstrip line at the bottom through by a pair of disconnected bow-tie slots etched on the middle ground plane. The proposed MTS is analyzed using characteristic mode analysis (CMA). The maximum current distribution of the characteristic modes which resonate at about 6.58 GHz is located at the edge patches rather than in the center. Therefore, the bow-tie slots etched at the center of the ground plane cannot effectively excite these modes, which leads to a radiation null at the upper band. A shorting probe is embedded in the bottom substrate to create a radiation null at the lower band. A preliminary filtering response is formed. And then, by loading two groups of split-ring resonators (SRRs) on both sides of the feedline, radiation nulls are generated at 3.68 GHz, 7.15 GHz, and 7.7 GHz, effectively enhancing the out-of-band rejection level, especially at the upper band. The simulated and experiment results show that the proposed antenna achieves impedance bandwidth (|S₁₁| ≤ −10 dB) over the frequency range of 5.7–6.1 GHz, with a peak gain of 8.7 dBi. Particularly, the out-of-band rejection level exceeds 22.4 dB and 24 dB, at the upper and lower band, respectively. Compared with some reported filtering antennas, the proposed antenna achieves a higher rejection. Moreover, the proposed antenna is simple in structure and easy to manufacture.