Low-RCS and High-Gain Circularly Polarized Metasurface Antenna.

High-gain planar antennas always contribute large radar cross section (RCS) to low-observed platforms. To solve this contradiction, we propose a novel design of circularly polarized metasurface antenna characterized by low RCS but high gain. Split ring resonators (SRRs) play a twofold role as the array elements for linear polarization and as the unit cells of metasurface for RCS reduction (RCSR). Four $2 \times 2$ arrayed SRRs are positioned with orthogonal orientations as a super-array element (SAE) and fed with a phase shift of 90° in between for left-handed circular polarization. On the other hand, based on its original arrangement, the open-circuited SAE is also designed to be the super-cell of a (0°, 180°) reflective checkerboard metasurface. Owing to anti-phase energy cancellation and scattering, both the in-band and out-of-band RCS can be dramatically reduced. As indicated by the measurements in antenna, the fabricated prototype operating in $X$ -band exhibits a combined bandwidth (3 dB axial ratio (AR), 3 dB gain drop, and −10 dB impedance matching) of 16% with a maximum realized gain of 17.9 dB. Besides, under normal illumination, the measured specular reflection has been reduced by 10 dB within 9.2–10.8 GHz and by 7.5 dB from 10.8 to 14 GHz. This design method simultaneously ensures high-gain antenna performance as well as meets the requirement for low RCS. [ABSTRACT FROM AUTHOR]