Chiral Dielectric Metasurfaces for Highly Integrated, Broadband Circularly Polarized Antenna

We report on the design of a low-profile integrated millimeter-wave antenna for efficient and broadband circularly polarized electromagnetic radiation. The designed antenna comprises a chiral dielectric metasurface built with a 2×2 arrangement of dielectric cylinders with slanted-slots at the center. A broadbeam high-gain with wide axial ratio (AR)<3 dB bandwidth was reached by pairing the electric and magnetic resonances of the dielectric cylinders and the slanted slots when excited by an elliptically polarized driven-patch antenna. This electric-magnetic pairing can be tuned by varying the cylinders diameter and the tilting and rotation angles of the slanted slots. The simulation results indicate impedance-matching bandwidths up to 22.6% (25.3–31.6 GHz) with 3-dB AR bandwidths of 11.6% (26.9–30.2 GHz), which in terms of compactness (0.95λ0×0.95λ0) and performance are superior to previous antenna designs. Since the simulations were performed by assuming materials and geometries easily implementable experimentally, it is hoped that circularly polarized antennas based on chiral metasurfaces can be integrated into 5G and satellite communications.

DOPING DEPENDENT ELECTRONIC STRUCTURE OF CUPRATES AND THE EFFECTIVE LOW ENERGY HAMILTONIAN FOR THE MAGNETIC PAIRING

The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and Tc(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the Tc(x) - optimal doping value becomes slightly lower and the maximum value of Tc become slightly higher.

ELECTRON DIFFRACTION STUDIES OF SUPERCONDUCTORS OF THE K-BA-BI-O SYSTEM AND RELATED OXIDES

The application of transmission electron microscopy in combination with physical-chemical methods has made it possible to discover a large number of discrete oxides of ordered structures in the Ba - Bi - O system, which is the parent system for the K - Ba - Bi - O superconducting system. Cation-ordered superconductors Ba 1-x K x BiO 3 with the crystalline structure of a non-cubic and layered nature have been synthesized. This result removes the crystallographic contradiction between bismuthate and cuprate superconductors that provides support to the existence of a common non-magnetic pairing mechanism.