An Ultrawideband Low-RCS Circularly Polarized Antenna Array Based on Hybrid Mechanism

In this article, a novel in-band and out-of-band low radar cross section (RCS) circularly polarized (CP) antenna array based on a hybrid mechanism of absorption and phase cancellation is proposed. The antenna scattering-reduction unit is a frequency-selective absorber-polarization converter (FSAPC) unit comprising a resistive metasurface (RM) unit, four frequency-selective surface (FSS) units, and four polarization-conversion metasurface (PCM) units arranged in cascade. The RM employs a parallel resonant structure comprising metal rings and parallel lines to create an in-band transmission window for the radiation while simultaneously absorbing the out-of-band electromagnetic waves. The modified PCM configuration is arranged in a diagonal configuration with cutting round arcs and serves two distinct functions. Primarily, it converts the co-polarized component of in-band incidence into a cross-polarized one. Second, the decomposition of the electric field enables the metal square to facilitate the conversion of the antenna-radiated wave from linear to circular polarization. Furthermore, the implementation of a counterclockwise feeding network is expected to enhance the circular-polarization performance. To verify the functional properties of the FSAPC structure, the properties of the constituent units and the FSAPC unit are elucidated and investigated in two dimensions: field and circuit, which are done based on the principles of double-port equivalent circuit and coupler theory. Furthermore, the slot antenna array is directly integrated with the metal reflector of the FSAPC in a chessboard configuration, thereby enabling the realization of the desired radiation performance. The simulation and measurement results demonstrate that the FSAPC-based antenna array is capable of achieving good left-handed CP radiation characteristics and also adept at reducing the RCS by over 10 dB across the 5.73–17.5-GHz range. The results demonstrate that the antenna array is capable of simultaneously achieving both stealth and radiation functions, rendering it an apt candidate for integration into modern weapon platforms.