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An ultrathin and broadband radar absorber comprising single-layer resistive frequency selective surface (FSS) is investigated in this letter. The resistive FSS layer constructed from resistive/low-conductivity treble-square loops is backed by a grounded foam material. Numerical results show that the proposed absorber can provide a 10-dB radar cross section (RCS) reduction for the conducting plate over the frequency range of 10.7-29 GHz, which is equivalent to a relative bandwidth of 92.2%. Moreover, the structure has the thickness of 2 mm (only 0.071 to 0.193 at lowest and highest frequencies, respectively). The equivalent circuit model is then used to introduce the working principles of the proposed absorber.

A circularly polarized switched-beam patch antenna array with butler matrix is designed and experimentally demonstrated in this letter. With suitable rotation technique, circular polarized radiation can be improved for beam steering. Also, this technique enhances the axial-ratio (AR) bandwidth within its scanning angle. Measured results showed this array has an impedance and AR bandwidth over a frequency range of 5.75-6.2 GHz when the main beam of array is scanned to different directions. Good agreement is observed between simulation and measurement.