Bandwidth Enhancement of Metasurface Antennas by Shifting and Reshaping High-Order Mode

In this letter, a new bandwidth enhancement method for metasurface antennas (MAs) is proposed, by shifting the distant resonant frequency closer and reshaping the distorted radiation pattern of a high-order mode (HOM). A dominant mode (DM) and a far-separated HOM of the MA are excited simultaneously by a half-square loop. By scaling the central, corner, and edge patches with nonuniform factors while hardly affecting the DM, the HOM is shifted to merge the DM under the guidance of the characteristic mode analysis. Moreover, in order to improve the current distribution, the distorted radiation patterns as well as the gain flatness under the HOM without affecting the DM, the U-shaped slots with a band-notch characteristic are introduced on the central patches. The proposed antenna is fabricated and measured. The measured results are coincidental with the simulated ones. The results also show that the proposed antenna has a 10 dB return loss of 35.8% (4.34-6.23 GHz) and an in-band gain of 6.8-11.3 dBi with a single-layer structure and low profile of 0.06 ?(0) (the free-space wavelength at the center frequency).