Circularly Polarized Electrically Small Antenna Using Chiral Metamaterials and Based on Characteristic Modes Theory

This paper presents a novel circularly polarized electrically small antenna that has been designed thanks to the Characteristic Mode Analysis (CMA). It is based on the energy compensation between two elements: a non-resonant dipole antenna and a chiral Metamaterial (MTM) in order to achieve a Circular Polarization (CP). First, the two elements are analyzed separately using CMA in order to analyze the physical behavior of both structures. Then, the inter modal coupling between the dipole and the MTM helix is studied between the different modes to propose a better understanding of the net stored energy compensation. The coupling between the two structures is through the magnetic and electric modes and it thus increases the overall efficiency. Circular polarization of the antenna is obtained through the chirality properties of the helix. The proposed antenna resonates at 2.35 GHz and has electrical sizes of $\lambda /15, \lambda /15$, and $\lambda /39$. The radiation pattern of the antenna is omnidirectional with a fair axial ratio for a circularly polarised antenna.