Broadband linear‐to‐circular polarisation conversion using the diamond‐shaped reflecting metasurface

Abstract

To overcome the narrow axial ratio (AR) bandwidth inherent in conventional linearly to circularly polarised converters, this research proposes a metasurface (MS) with a diamond‐shaped configuration that can mitigate the effect of surface wave (SW) along the MS edge and achieve a wider 3 dB AR bandwidth. The diamond‐shaped MS structure is realised by slanting a square MS by 45°, and it consists of constituent unit cells of rectangular and arbitrary shapes. The rectangular unit cells are positioned 45° to the square dielectric substrate, and the unit cells along the MS edge are partially cut into arbitrary shape to be perfectly aligned along the edge. The 3 dB AR bandwidths and degradation of the MS are characterised by SW and magnetic current distribution. Simulations are carried out and an MS prototype is fabricated to verify the results. The effects of partially cut unit cells (PCUCs) along the MS edge on the SW are characterised. The simulation and measured 3 dB AR bandwidths of the diamond‐shaped MS are 37.6 and 28.8%, respectively. The novelty of the proposed diamond‐shaped MS polarisation converter lies in the implementation of arbitrary‐shaped PCUCs and the use of the diamond‐shaped configuration in place of conventional square geometry to realise wider AR bandwidth.

Broadband Circularly Polarized Microstrip Patch Antenna With Diamond-Shaped Artificial Ground Structure

“…5(c As described above, the AR is deteriorated in an AGS due to resonances at some frequencies; however, a DAGS can suppress these extra resonances. To determine the mechanism involved, simulated magnetic current distributions between the unit cells (copper) on the substrate surface of the AGS, LDAGS, and SDAGS were observed [7], [22], [23] at the deterioration frequencies. As shown in Fig.…”

“…In both structures, the strength of the magnetic current is balanced in the x and y directions. Moreover, strong magnetic currents are mitigated along the edges due to the effect of the partially cut unit cells along the contours of the DAGSs [7].…”

“…Thus, the dependence of the AGS characteristics on the geometry of the ground plane and the dimension of the unit-cell array should be taken into account. A modified rotated AGS, where the rectangular unit cells are rotated by 45° with respect to the sides of the rectangular ground plane, named a diamond-shaped AGS (DAGS), was developed to reduce the unwanted resonances that affect the broadband CP characteristics [7], [19]. The unwanted resonances in a DAGS are weak because the resonance of the magnetic current, which depends on the rows and columns, is spread over several frequencies.…”