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 degrees 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 degrees 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 he maintained at the same time.