A Wideband Circularly Polarized Antenna Array Loaded With Dual-Layer Metasurface

A novel wideband circularly polarized (CP) microstrip antenna array loaded with dual-layer Metasurface (MTS) is pro-posed. The dual-layer rhombic MTS with asymmetrical perturbationsis designed to excite two CP modes at different frequencies. Moreover, a hybrid phase shifting (HPS) strategy is proposed and taken to incorporate unequal cross-couple slots into the radiating patches to achieve the phase shifting condition for wideband CP antenna element. Simulated results for the proposed element show that an axial ratio (AR)bandwidth of 40.0% (12.14-18.21 GHz) is achieved with good impedance matching. A 4x4 CP antenna array composed of four 2x2 subarraysfed through a sequential rotation network is designed and fabricated. The measured results show that a-10 dB impedance bandwidth of 67.2% (10.21-20.56 GHz) along with an AR bandwidth of 65.5%(10.81-21.25 GHz) and 3-dB gain bandwidth of 53.1% (11.46-19.74 GHz)as well as a peak gain of 17.19 dBic have been achieved. Parasitic corner-cut square rings (CCSRs) are incorporated to reduce the sidelobe levels (SLLs) at high frequencies and make them below-10 dB, as usually achieved by relatively narrow-band arrays, and finally-11.3 dB is achieved