Circularly polarized microstrip antenna with electrically large property by using tilted periodical I‐shaped resonant inclusions

Abstract

Usually circularly polarization (CP) of microstrip antennas is designed by using perturbed radiating patch or phase-shift feeding network. In this paper, perturbation of inter-medium metamaterial layer is proposed to tune the polarization characteristics of square microstrip antenna. As given in former design, effective media parameters of one I-shaped metamaterial is in the band of ε>0 and μ<0 and electrically large property (ELP) of more than 4 times larger than conventional fundamental mode is achieved. By changing the geometry and placement location of periodical resonant inclusions, linear polarization as well as CP, either left-handed CP (LHCP) or right-handed CP, can be obtained without changing the square radiating patch and the feeding structure. Effective media parameters of different types of metamaterial are also extracted to confirm that ELP can be maintained. Finally, by using 45° tilted periodical I-shaped resonant inclusions, one prototype with LHCP is fabricated for verification. Good agreement is achieved between the simulated and measured results. The proposed method gives new option to design antennas with different polarization states in millimeter wave or even terahertz wave band in future.