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

Abstract

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° 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.