An Ultralow-Profile Folded Transmitarray Antenna with Low RCS Based on Metasurface and Rasorber

In this paper, we propose a novel linearly polarized folded transmitarray antenna (FTA) with low radar cross-section (RCS) and ultralow profile. It is engineered by combining a frequency selective rasorber (FSR) for absorbing out-of-band linearly polarized electromagnetic (EM) waves, a transmission and reflection (T-R) metasurface for independent manipulation of x- and y-polarized incident waves, a polarization conversion (PC) metasurface and a horn antenna for feeding. The antenna operates in two distinct radiation and scatting modes. In radiation mode, the spherical electromagnetic (EM) wave generated by the feed horn is transformed into a high-gain pencil-shaped beam. The peak gain of 22.9 dBi at 14.2 GHz and 1-dB gain bandwidth of 5% are obtained. Significantly, the incorporation of triple phase compensations via both T-R and PC metasurfaces further reduces the antenna profile to merely 1/7 of its initial focal length. In scatting mode, in-band RCS reduction is realized through antenna matching and EM scattering effect of the T-R metasurface. Furthermore, a 10-dB out-of-band RCS reduction is achieved within 5.5-12.6 GHz under x and y-polarized incident waves relying on FSR.