Design of metasurface polarization converter for near-field application; stacked conical horn antenna for circular polarization

摘要

In this article, a three-layer transmission mode linear to circular polarization converter (TMCP) is proposed with low-level reflection coefficient and axial ratio (AR) at 9 GHz. Each layer of the proposed TMCP consists of microstrip patches and lines, providing inductive TM impedance and capacitive TE impedance on each layer to produce 90 degrees out of phase between TE and TM electromagnetic waves. By removing the middle layer of the proposed metamaterial, a two-layer TMCP with low-level axial ratio at 8 GHz is obtained. However, the proposed two-layer TMCP suffers from disagreements between the reflection coefficients of the TE and TM modes, which produce fluctuations on the AR results in the near-field application. Low-level reflection coefficient and AR at 9 GHz achieved from the three-layer TMCP, indeed, make it efficient for the near-field of a horn antenna. Unit cells of the two-layer and three-layer TMCPs consisting patches and lines are simulated using periodic boundary conditions. In addition, the patches and lines are printed on a FR4 substrate and cut out in circle shapes. The three substrates are arranged at the determined separations and then installed in front of a profiled conical horn antenna. The measured AR of the antenna stacked by the three-layer TMCP is below 2 dB from 8.45 up to 9.6 GHz.