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 x 2 arrayed SRRs are positioned with orthogonal orientations as a super-array element (SAE) and fed with a phase shift of 90 degrees 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 degrees, 180 degrees) 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.