Superstrate-based Low RCS Cavity-Backed Archimedean Spiral Antenna

Spiral antennas are broadband circularly polarized antennas extensively used in radar warning systems, direction-finding radars, electronic warfare (EW) systems, etc. When EW antennas are mounted on a stealth platform, these antennas are required to have low radar cross-section (RCS) besides having a wideband operating frequency, high gain, low axial ratio (AR), and voltage standing wave ratio (VSWR). This paper presents the electromagnetic (EM) design of a low observable right-handed circularly polarized (RHCP) cavity-backed Archimedean spiral (CBAS) antenna with VSWR<2.2, AR<3 dB, and +ve gain over the frequency range of 2GHz to 18 GHz. In order to reduce the structural RCS of the designed CBAS antenna, a three-layered metasurface-based superstrate is placed at an optimum height (22mm) from the antenna aperture. It is shown that the addition of superstrate over the CBAS antenna has not degraded the EM performance of the antenna in terms of VSWR, axial ratio, gain, and radiation pattern. Monostatic/bistatic RCS of the CBAS antenna has been simulated for an RHCP plane wave incidence over 1-18 GHz. An RCS reduction of about 7dB (average) has been achieved without degradation in the radiation performance.