Low-Profile Wideband Circular Polarization Metasurface Antenna With Characteristic Mode Analysis and Mode Suppression

In this letter, a wideband circular polarization (CP) metasurface (MS) antenna is proposed, which is composed of a centrosymmetric structure with a mode suppressor and an asymmetric aperture-coupled feed structure separated by dielectric substrates. Based on the characteristic mode theory, the aperture-coupled feed structure consisted of an L-shaped slot and a microstrip line is employed to excite two orthogonal modes, which have a 90° phase difference to obtain CP radiation. Meanwhile, two methods have been proposed to expand CP bandwidth: one is the direct suppression of characteristic mode by decreasing the overlap frequency of operating and nonoperating mode. The other one is indirect suppression using a mode suppressor. Finally, the MS antenna with a low profile of λ0 × λ0 × 0.075 λ0 at 5 GHz is fabricated and measured. The measured results show that the proposed antenna has a 3 dB axial ratio bandwidth of 45.2% from 4.1 to 6.5 GHz and an impedance bandwidth of 41.8% from 4.1 to 6.31 GHz, and a peak gain of 7.94 dBic at 5.9 GHz.