A Compact Circularly Polarized Multibeam Antenna Using Defected Polarization Conversion Metasurface

In this letter, a four-beam circularly polarized (CP) antenna in the Ku-band based on metasurface (MS) is proposed. It consists of a defected polarization conversion metasurface (PCM) and a feeding structure. The PCM is composed of centrosymmetric units, each of which contains a pair of square patches and a pair of L-shaped patches. When it is placed above the feeding structure, the linearly polarized (LP) wave is converted into a CP wave, and the gain is also enhanced. Furthermore, through loading stubs on the microstrip feeding lines and modifying the PCM as a defected PCM by removing some units from the MS, both the back and sidelobe levels are reduced. The realized antenna has a compact dimension of 1.05 lambda(0) x1.05 lambda(0) x0.12 lambda(0). It hasa-10 dB impedance bandwidth from 12.69 to 13.38 GHz (5.3%) and a 3 dB axial ratio bandwidth from 12.69 to 13.88 GHz (9.1%). When the four ports are excited, the four beams point at (theta, phi)=(40 degrees, 105 degrees), (40 degrees, 165 degrees), (40 degrees, 285 degrees), and (40 degrees, 345 degrees), respectively. The four beam directions may be altered by readjusting the coupling slots in the ground plane. The gain in the working band reaches 8.27 dBi.