Frequency selective superstrate absorber for wideband RCS reduction of metal‐backed antennas

The use of a resistively loaded frequency selective surface (FSS) superstrate is reported as a means to reduce the radar cross-section (RCS) of metal-backed antennas. The design methodology is demonstrated by creating a low-profile absorber which exhibits a transmission window covering the working frequency band (10-10.2 GHz) of a 4 x 4 microstrip patch array. Placing the structure lambda/2 above the radiating aperture is shown to reduce the antenna gain by less than 2 dB and have minimal impact on the shape of the beams which are directed at 0 degrees and tilt angles of 22.5 degrees and 45 degrees. Moreover 90% radar backscatter suppression is achieved over 92% of the frequency range 8.85-24 GHz. The perforated metal-backed FSS superstrate was inkjet printed on a 140 mu m thick polyethylene terephthalate (PET) sheet and the conductivity of the silver plating adjusted to achieve the required 40 omega/sq surface resistance. The experimental results obtained for the standalone microwave absorber, and when integrated with the antenna, are shown to be in close agreement with the computed reflectivity and far field patterns.