Reducing the RCS of a MIMO antenna using an angularly stable FSS

A systematic design procedure for reducing the radar cross section (RCS) of a multiple-input multiple-output (MIMO) antenna is presented in this paper. The RCS reduction was achieved at 11.3 GHz, which was out-of-band compared to the antenna's working frequency of 2.18 GHz. The design flow started with developing an isolation-enhancement network for the MIMO antenna that did not disturb the RCS reduction process. An incident- and polarization-angle-insensitive frequency-selective surface (FSS) was next designed. The conventional ground plane of the MIMO antenna was replaced by an FSS array. The designed FSS was introduced in such a way that the antenna's characteristics and isolation among the antenna ports were preserved by achieving the RCS reduction of an antenna at the bandpass frequency of the FSS. The proposed FSS was angularly stable, and hence an almost constant RCS reduction was found for most of the incident angles. The final proposed low-RCS MIMO antenna was fabricated and measured to validate the simulation results.