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
λ
₀
× 1.05
λ
₀
× 0.12
λ
₀
. It has a −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 (
θ
,
φ
) = (40°, 105°), (40°, 165°), (40°, 285°), and (40°, 345°), 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.