X-Band and Circularly Polarized Antenna With Inborn RCS Reduction

In this letter, an artificial magnetic conductor (AMC) structure based on circular-loop patch, and a grounded substrate, are designed to realize 180° reflection phase difference in an ultrawide frequency band. This letter applies phase property of this AMC structure and grounded substrate to redirect the scattering fields of a radar target to reduce its radar cross section (RCS). This method of RCS reduction can be realized by covering with a chessboard surface composed of the AMC structure and grounded substrate, so the RCS reduction in a wide frequency band can be achieved as well. Compared with the same-sized metal surface, this proposed chessboard surface can reduce RCS drastically from 8 to 20 GHz. Meanwhile, this surface also can be used as an antenna. By precisely designing feed network, the feed of two parts of antenna can achieve 90° phase shift, so the circular polarization (CP) antenna can be designed as well. The CP antenna has a low profile. The simulated impedance-matching frequency band is from 9.3 to 10.9 GHz, and the simulated axial-ratio bandwidth is from 9.25 to 10.02 GHz. Excellent agreement is obtained between simulation and measurement for CP antenna and chessboard surface. Such method will give a way for integrated design of antenna and metasurface, so the RCS can be reduced, and the radiation properties can be maintained at the same time.