Adaildo G. D'Assunção

A new FSS design proposal for UWB applications

This work presents a new proposal for Frequency Selective Surface (FSS) design for Ultra-Wideband (UWB) applications. The new FSSs consist of an array composed by the association of two patch elements per cell: a square loop and a crossed dipole. These structures are called Crossed Loops and have the objective of increasing the bandwidth of the square loop and the crossed dipole, when analyzed separately. Simulated results of the transmission coefficients are obtained using the Ansoft Designer¿ commercial software. Some of the FSSs tested were fabricated in order to make an experimental analysis with the measured results and to validate the new proposal. In particular, the presented results for the transmission coefficient of a built FSS prototype indicate a percent bandwidth 52.4%.

Efficient ray-tracing method for indoor propagation prediction

This work presents an efficient implementation of the 2.5D ray-tracing method for modeling indoor propagation. The implementation is made by means of graphic software tools using the shooting and bouncing rays (SBR) technique, in combination with the uniform theory of diffraction (UTD). A database is built to record geometrical characteristics and environment materials that allow flexibility and robustness to model news scenarios. Some comparisons between computed predictions and measurements show good agreement. The theory is also verified by comparison with previously published data.

Wide stop-band cascaded frequency selective surfaces with Koch fractal elements

Numerical and experimental investigations are presented for a cascaded frequency selective surface (FSS) with Koch fractal conducting patch elements. The work is developed in two steps. In the first step two Koch fractal FSS screens are designed using the Ansoft Designer™ software. In the second step these FSS are cascaded and separated by an air gap layer to improve the bandwidth behavior. The structures are cascaded using Teflon spacers and screws to obtain the air gap. Thereafter, a numerical cascading technique is used to analyze the effect of the air gap between the cascading structures.

Design of frequency selective surfaces using a novel MoM-ANN-GA technique

This work describes a new application of genetic algorithm (GA) for frequency selective surfaces (FSSs) design. The works innovation was the introduction of an artificial neural network (ANN) as a fitness function into GA. The ANN model was trained with accurate data provided by FSSs simulations using the method of moments (MoM). The founded advantages in the design of FSS devices using the technique through of genetic algorithms and neural networks are discussed and the results are presented as way to validate the new proposed technique.

Analysis of high T/sub c/ superconducting microstrip antennas and arrays

The analysis of microstrip antennas with superconducting films is performed in the Fourier domain. The method of moments, the vector Hertz potentials and the complex surface resistance model are used. The resonant frequency and the quality factor of the superconducting microstrip antenna are obtained as function of the temperature and of the geometrical parameters. It is shown that the full-wave analysis presented here gives numerical results which are in excellent agreement with the measured ones, which are available in the literature. The radiation pattern for a HTS microstrip antenna linear array is also obtained.

Full-wave analysis of microstrip lines on ferrite and anisotropic dielectric substrates

Microstrip lines on ferrimagnetic and uniaxial anisotropic dielectric substrates are examined. Hertz vector potentials oriented along the magnetization direction for the ferrimagnetic substrate and along the optical axis for the uniaxial anisotropic dielectric substrate are used to obtain the dyadic Greens functions in the Fourier transform domain. Galerkins method is used to obtain the frequency behavior of the propagation constant. Curves for a few cases are shown as examples. >

A comparative study of three ultra-wideband log-periodic microstrip antenna arrays

This paper described the design, simulation and fabrication of three ultra-wideband log-periodic microstrip antenna arrays. A comparative study is presented between arrays using rectangular, square and circular patch elements and varying the number of elements (5, 10 e 15). Electromagnetically coupled microstrip patches had been used as radiating element of arrays. The frequency responses of these arrays are analysed using the Ansoft Designer¿ commercial software that implements the method of moments. After the simulations were completed, three prototypes were constructed and measured using a vector network analyzer. The results for the -10 dB return loss bandwidth of the antenna arrays are presented. The good agreement between theoretical and experimental results for the built antenna prototypes validated the used methodology.

Scattering Parameters of FSS on Anisotropic Layers at Millimeter Wave Frequencies

The analysis of periodic structures on anisotropic substrates is presented for incident millimeter waves. Frequency selective surface structures composed by a periodic array of conducting crossed dipoles on anisotropic layers are analyzed. A full-wave analysis for the problem of scattering is performed. The formulation uses the moment method in combination with the immitance approach, in the Fourier domain, to determine the scattering parameters of the considered structures. A set of entire-domain type basis functions is used in the expansion for the unknown induced current. This analysis is computationally efficient, and its accuracy is verified by the agreement between results obtained in this work and those available in the literature, for particular cases.

Small size quasi-fractal microstrip antenna M1 EBG-GP

A new patch antenna using the Minkowski fractal curve and Electromagnetic Bandgap structure on plane ground is proposed. The design was based on HFSS and a prototype was built and measured in order to validate the numerical results. A better impedance matching for the device was obtained using the inset-fed technique. The measured return loss for the proposed antenna at the resonant frequency is lower than �15 dB. The M1 EBG-GP antenna resonant frequency is lower than that of a corresponding rectangular inset-fed patch antenna. This results in a reduction of 35.6% for this antenna resonating at 2.45 GHz (ISM band).

A new compact koch fractal patch antenna on an EBG ground plane

A new antenna with Koch fractal patch elements of the first level (KR1) and electromagnetic bandgap in the ground plane (EBG-GP) is proposed in this paper. The design is based on Ansoft HFSSTM software and in order to validate the model several prototypes are built and measured. A better impedance matching for the device is obtained using the inset-fed technique. The measured return loss values for the proposed antennas at the resonant frequencies are lower than -20 dB. The KR1 EBG-GP antennas show corresponding resonant frequencies values lower than the rectangular patch antennas with inset-fed. That results in a size reduction factor around 28% for these structures resonating at 2.45 GHz.