Cynthia Junqueira

The step by step development of NRW method

This paper explains in details the NRW method highlighting its mathematical procedure and analyzing the most important points and limitations to characterize the complex permittivity and permeability of dielectrics. The step by step procedure help the researchers to well understand the physical phenomenona involved and also is a tool to facilitate its implementation. Explanations on the limitations of the method in situations where the return loss tends close to zero and the disambiguation phase using two samples are detailed. The non-iterative method was evaluated as a candidate to characterize materials for radome applications.

Immune-inspired Dynamic Optimization for Blind Spatial Equalization in Undermodeled Channels

In this work, we propose an evolutionary-like approach to the problem of blind adaptive spatial filtering that is based on the decision-directed criterion and on the dopt-aiNet, an artificial immune network conceived to perform multimodal search in dynamic environments. The proposal was tested under static and time-varying undermodeled channel models, and, in all cases, its ability to find and track a solution close to the Wiener global optimum was attested. The obtained results reveal that the dopt-aiNet may decisively enhance the performance of adaptive arrays in scenarios built from elements that are representative of some aspects of real-world communication systems.

A free space measurement approach for dielectric material characterization

The free space method allows nondestructive dielectric characterization of materials in a wide range of frequencies and temperatures, which is basic to several applications, as the development of radomes for aerospace proposals. This paper comprises the free space method from an initial procedure, the TRL calibration, to the permittivity calculation by the NRW method, including the software implemented and its practical validation with specific materials.

A Proposal for Blind Fir Equalization of Time-Varying Channels

The multimodal and time-varying aspects of blind equalization problems in communication systems are treated here by means of an immune-inspired strategy capable of estimating the coefficients of the FIR equalization filter in an unsupervised manner. The associated optimization problem is solved by means of a population-based search technique characterized by a dynamic control of the population size and diversity maintenance. Static and time-varying channels have been proposed in simulated scenarios, aiming at indicating the tracking capability derived from the adaptive adjustment of the coefficients of the blind equalizer

ℓ0-optimization for channel and DOA sparse estimation

This paper is devoted to two classical sparse problems in array processing: Channel estimation and DOA estimation. It is shown after some background and some recent results in ℓ0 optimization how this latter can be used, at the same computational cost, in order to obtain improvement in comparison with ℓ1 optimization for sparse estimation.

Enhancing DSSS-signals channel estimation through compressive sensing

A new approach for channel estimation, based on the concept of compressive sensing is presented for situations where signals are DSSS transmitted. Compressive sensing encompasses elegant mathematical background where the information of the sparse characteristic of the signal is used to create an efficient representation of it using fewer measurements than required by the Shannon-Nyquist criterion. The reconstruction is performed through linear programming or greedy algorithms. In this paper, we demonstrate that compressive sensing can enable reduction in the analog-to-digital sampling rate, allowing the design of simpler and cheaper receivers, while keeping or improving resolution in the DSSS channel estimation.

Microwave absorber materials characterization: bulk absorbing and electrical/magnetic parameters

Microwave absorber materials are used extensively in anechoic chambers for antenna measurement, to emulate free-space conditions. They are also used to suppress unintended radiations in consumer electronic products (so that they present conformity to existing regulations) and other applications. Their characterization usually shows the amount of damping in a certain frequency range, and it depends on the materials used in the mixture and its overall geometry. This article deals with Brazilian and international manufactured, low cost absorbing materials, characterized in both bulk format (damping) as well as its material parameters (electrical permittivity and magnetic permeability).

An evolutive algorithm for blind adaptive beamforming in GPS applications

In this work we propose an alternative approach to the problem of digital beamforming. We employ an evolutive algorithm, named opt-aiNet, to optimize the directed-decision (DD) criterion, a well-known equalization criterion, in order to determine the optimal coefficients of the antenna array. The approach is applied to a GPS application scenario, where the multimodal search capability of the opt-aiNet algorithm is used to simultaneously find the coefficient vectors that capture the signals coming from all the visible satellites

A polygonal immune-inspired framework for broadband patch antenna design

In this work, we present a novel paradigm for the bottom-up project of patch antennas. This paradigm is based on a polygonal immune-inspired framework, being the chosen artificial immune system the CLONALG algorithm. In order to employ this new strategy, it was necessary to build a software platform to properly use the electromagnetic CST solver and provide a source engine to evolve antenna designs. We believe this development to be a contribution per se. The presented results show that the method was able to obtain low profile antennas with broadband characteristics by the exploration of unconventional patch shapes.

Accuracy of GRL calibration considering time domain gating for the calculation of permittivity parameter in free space technique

An experimental method for increasing the accuracy of GRL calibration is presented. This paper shows how to make correct time gating, achieving better results of GRL calibrations for calculating permittivity parameters in free space technique.