An Integrated Low-RCS Circularly Polarized Reconfigurable Transmitarray Antenna Based on a Multimode Metasurface

In this paper, an integrated low radar cross section (RCS) circularly polarized reconfigurable transmitarray antenna based on multimode metasurface is proposed. This approach fully leverages the mode resources of the multimode metasurface, assigning distinct functionalities to different modes through appropriate excitation mechanisms. As a result, the stealth and radiation properties are integrated into the same structure. To demonstrate the feasibility of this concept, a specific design is presented and analyzed in detail. The element consists of three layers: the top layer is a centrally-slotted, diagonally oriented patch; the middle layer comprises a phase delay line and a ground plate with a hole; and the bottom layer features another centrally-slotted patch, which is aligned with the coordinate axes. Two metallic posts connect the top and bottom patches, providing structural integrity and electrical continuity. Additionally, four PIN diodes are incorporated into the bottom patch to enable 1-bit transmission phase reconfiguration based on the current inversion method. Moreover, two types of elements, A and B, are designed. The key difference between them lies in the orientation of the top-layer patches, which are perpendicular to each other, and the phase delay lines, which differ by a quarter-wavelength. Then, a 16×16 prototype is then fabricated using a combination of elements A and B. Simulated and measured results confirm that the proposed design achieves good left-hand circularly polarized radiation and ±45° beam scanning capability within 6.75~6.95 GHz. Additionally, the RCS is reduced by more than 10 dB within 4.44~6.26 GHz and 8.9~12.1 GHz.