Broadband and High-Gain Circularly-Polarized Antenna With Low RCS

In this paper, a wideband circularly polarized (CP) antenna with a low radar cross section (RCS) and high gain properties is investigated. The proposed antenna is based on a combination of the Fabry–Perot cavity (FPC) and sequential feeding technique. The purpose of this antenna is to produce CP with high directive gain over a wide bandwidth while preserving low RCS. The principle of the FPC and resonance is achieved by applying one frequency selective surface (FSS) metasurface. A microstrip slot array operating at the Ka-band, excited by a sequentially rotated feeding network, is designed and fabricated. It is indicated that all the merits mentioned above can be obtained over a broad frequency band by designing a suitable FSS metasurface and modifying the feeding lengths to adjust desirable phase. RCS reduction is realized by 180° ±37° reflection phase variations between adjacent FSS unit cells on the metasurface. The experimental results show that the gain of the antenna with the metasurface is at least 7 dB greater than that of the primary antenna with a peak value approximately 20 dB at 28.5 GHz. In addition, bandwidths of 3-dB gain, impedance ( $\vert \text{S}11\vert \le -10$ dB), and axial ratio ≤3 dB are ranged from 27.5 to 33.5 GHz (19.7%), 26.7 to 34.2 GHz (24.6%), and 26.8 to 33.1 GHz (21%), respectively. The monostatic RCS reduction for a normal incidence is effectively suppressed from 28 to 48 GHz (52%).