Low-Profile Circularly Polarized Array with Gain Enhancement and RCS Reduction Using Polarization Conversion EBG Structures

A planar antenna array based on checkerboard polarization conversion electromagnetic band-gap (EBG) structures with wideband circular polarization and low radar cross section (RCS) is presented. The array is formed by 2×2 circularly polarized (CP) element antennas fed with a sequential feeding network. On the one hand, CP radiation is obtained due to the polarization conversion characteristic of the metamaterials. A sequentially rotated feeding network is employed for wide operating bandwidth, polarization purity and radiation pattern symmetry. Measured results show that the array has a wide usable bandwidth of 18.4%, the common part of an impedance bandwidth of 37.3% (4.80-7.00 GHz), a 3-dB axial ratio (AR) bandwidth of 22.5% (5.00-6.27 GHz) and a 3-dB gain bandwidth of 18.4% (4.94-5.94 GHz). On the other hand, the checkerboard arrangement of the EBG structure generates both an in-band and a partial out-band RCS reduction under normal incidence for both x-and y-polarizations. Besides, the proposed array achieves a significant gain enhancement compared to the traditional slot array. The experimental and simulated results are in good agreement.