Antônio Tomaz

Refractive properties of wire-grid metamaterials

This paper reports on a quantitative analysis of the electromagnetic properties of an arrangement of periodic metallic grids devised to provide in the 12.5–20.0 GHz frequency range a refractive index less than unity with view to enhance the functionalities of microwave horn antennas. Based on an analytical model, the ultra-refractive behavior of the metamaterial structure is demonstrated by the impedance and refractive index values retrieved from simulated scattering parameters.

Experimental investigation on the radiation pattern of a horn antenna loaded by a wire medium

The present paper reports on the design, implementation, and tests of a wire medium to experimentally verify its effects on the performance of a standard X-band horn antenna loaded by such a bulk metamaterial medium. The wire medium is composed of a periodic array of 0.5-mm-diameter metallic wires arranged in a square pattern with lattice spacing of 10.0 mm and hosted in Styrofoam plates. Experimental measurements of the radiation pattern at 11.70 GHz show an enhancement of the side lobes while maintaining the antenna peak gain, indicating that the metamaterial wire medium introduces negligible loss into the loaded antenna.

Refractive properties of artificial dielectrics consisting of a periodic wire medium

This paper examines the refractive properties of a wire medium designed to operate in the X-band for directive antenna application. The periodic structure is implemented using 0.5-mm-diameter copper wires arranged on a square lattice with spacing of 10 mm, yielding a cutoff frequency of 7.7 GHz. Through numerical experiments, the refractive index is calculated as n = λ₀/λ_g, where λ₀ and λ_g are the free-space and guided wavelengths, giving an average value of n = 0.6 over the 8-12 GHz frequency range.

Focusing microwaves by a periodic arrangement of conducting wires

Microwave focusing in the 8-12 GHz frequency range to produce localized energy concentration is achieved by using a periodic arrangement of thin conducting wires. The wire medium is implemented with 0.5-mm-diameter wires symmetrically arranged in a square lattice with spacing constant of 10.0 mm. It is shown that the amplitude of the electric field in the central spot of the focused beam is 2.7 times higher than the corresponding amplitude of input plane wave.

Experimental measurements of radiation patterns of a wire-medium loaded X-band antenna

This paper reports on the radiation patterns measured on a X-band antenna loaded with a periodic array of metallic wires. Design details of the wire medium to provide low return losses in the range 8 to 12 GHz are given. Using different test setups, the diagram patterns are measured at different frequencies associated with minimal return losses. Radiation characteristics of the loaded antenna are discussed.

Wire grid metamaterial for directive emission

In this work are reported the electromagnetic properties of an arrangement of periodic metallic grids devised to provide in the 12.5-20.0 GHz frequency range a refractive index less than unity with view to enhance the functionalities of a Ku-band horn antennas. The ultra-refractive behavior of the metamaterial structure is demonstrated by the impedance and refractive index values retrieved from simulated scattering parameters.

Microwave propagation experiments on a gradient array of split-ring resonators

A study of a gradient array of split-ring resonators is conducted experimentally to verify the transmission band resulting from the electrical and magnetic responses. Microwave propagation due to the magnetic response in a X-band waveguide below cutoff is obtained at about 4.40 GHz with a large bandwidth of 1.08 GHz and a neat intensity of 65 dB above the floor noise when tuned by a magnetic loop. Measured transmission bands corresponding to magnetic and electrical frequencies are compared with simulation model with good agreement.