José C. A. Santos

Path Loss Measurements of HF/VHF Land Links in a Brazilian Atlantic Rainforest Urban Site

This letter describes a recent HF/VHF radio signal measurement campaign carried out in a small urban reservation of the Atlantic Rainforest at Rio de Janeiro, Brazil. Motivation came from the lack of detailed reports on this type of work, considering the Brazilian forest scenarios. The collected data are presented in the form of path loss versus distance and frequency and are compared to Tamirs model. Good adherence was observed between measurements and calculated values from the reference model, despite the relatively short distances, with mean errors no greater than 3.0 dB and standard deviations less than 4.3 dB.

Proficiency testing of electromagnetic compatibility (EMC) labs in Brazil by measurement comparisons

This work reports the analysis and main results of a recently concluded proficiency testing round with the major electromagnetic compatibility (EMC) laboratories in Brazil. Seven labs conducted radiated emission measurements at their test facilities under the coordination of an independent third party supervised by the Brazilian accreditation body, INMETRO. Six of them are currently the only labs accredited on EMC measurements in Brazil. The guidelines of international standards such as ISO/IEC Guide 43 and ISO 13528 were followed, while the scope of the tests focused on EMC compliance of information technology devices, based on CISPR 22. A multi-tone signal generator was specifically designed and assembled for the present proficiency testing conditions. Statistical metrics such as z-score and normalized error have been adopted to assess global and individual performances of the participant laboratories. The normalized error indicated 10 unacceptable results out of 35 results, while only 3 out of 35 z-scores were out of the acceptance range. Considering that the participant labs are actually only for test measurements (not for calibration), the overall performance may be taken as satisfactory, based on the fact that the z-score should be used in this case.

A dual band steerable cell phones jammer

Efficient jamming of cell phones is highly demanded by security authorities in Brazil, especially within prisons. In this context, a dual band steerable jammer structure is proposed in this work. A single spatial filter was designed to operate simultaneously on both cell phone frequency bands, based on the methodology of null steering beamforming. Hardware and software issues of the proposed jammer are addressed. The jammer directional performance is illustrated by simulated beam patterns, which led to acceptable results.

Practical design of a broadband modified monopole by the use of staircase parasitic rings

The present paper discusses the use of parasitic elements to significantly increase the bandwidth of an antenna. In a recent work, the use of staircase metallic rings around a monopole antenna was proposed, leading to bandwidth increments of almost 10 times. However, there were a few shortcomings regarding implementation and experimental validation of that approach. This text reassesses it, with special attention to practical aspects. More specifically, a solid dielectric base is proposed to sustain the rings around the monopole. A prototype has been assembled and tested, with increase in bandwidth comparable to the one achieved in that work.

On the use of Tamir's model for site-specific path loss prediction of HF/VHF systems in forests

One of the most referenced analytical methods to calculate the HF and VHF radio propagation loss in forests is Tamirs model. Though it is very straightforward for point-area radio coverage planning, its extension for site-specific predictions is actually an open problem. In the present work, a heuristic approach is proposed to this matter, when digital terrain and treetops heights models are available. Preliminary outcomes were computed by a Matlab code implementation of the adapted model. Coherent results were observed, with a “height gain” typical of site-specific methods clearly standing out.

VHF/UHF urban sites coverage planning with special care to mixed terrain transitions

This work addresses the main features of a coverage planning algorithm for VHF/UHF low power radio communications systems operating at urban sites, in which special attention was given to mixed terrain clutter transitions. Most of the available commercial prediction tools adopt rough solutions to some problems derived from the use of semi empirical models with geographical databases. The influence of mixed-path terrains and the path loss due to dense vegetation are typical related examples of usually overlooked aspects. The developed code is based on Hatas semi-empirical approach with additional point-to-point adjusts, and includes specific procedures for those two aspects. It has been developed as Matlab™ routines, which were evaluated comparing its outputs to the ones obtained from the use of a commercial planning tool. Results were coherent with the specific features of the site chosen for the analysis.

RF jamming coverage prediction at mixed-path urban scenarios

This work describes an algorithm for VHF and UHF jamming coverage prediction at mixed-path urban scenarios. The proposed algorithm comprised propagation aspects usually overlooked: the influence of mixed paths and dense vegetation. It was developed as Matlab codes to perform coverage prediction for the jammer and the target system, and to compute the respective jamming to signal ratio (J/S) for the analyzed region. Jamming coverage is determined comparing J/S to the target system effective jamming threshold. The proposed tool is useful for jamming operation planning, since it is able to point out unobvious coverage spots that otherwise would be unnoticed.

Tópicos de Gliceroquímica: Utilização de Glicerol como Solvente Verde em Reações Assistidas por Micro-ondas

O glicerol e um triol cuja oferta no mercado se encontra em crescimento continuo por ser produzido como subproduto na industria do biodiesel. Disso surge a necessidade de se encontrar aplicacoes para o glicerol que absorvam toda esta nova quantidade produzida. Uma das aplicacoes que vem despontado na literatura, e a utilizacao do glicerol como solvente ou co-solvente em processos quimicos. Solventes sao utilizados em processos quimicos para auxiliar fenomenos de transferencia de massa e de calor, facilitar separacoes, purificacoes, etc. Uma vez que o glicerol possui propriedades fisico-quimicas e dieletricas interessantes, alem da origem renovavel, e a tecnologia de micro-ondas estar se provando mais verde que as colocadas atualmente, uma conjuncao de ambos se mostra uma situacao sinergica desejavel. Logo, a contribuicao deste trabalho e fazer uma revisao da literatura destacando exemplos de aplicacoes, onde esta situacao sinergica esta presente.

An efficient single receiver high resolution DOA estimation algorithm for modulated signals

Direction finding techniques can be applied to a number of military and civilian systems, such as radar, sonar, and radio communications. It aims at finding the Direction of Arrival of an electromagnetic source for positioning purposes. Direction finding systems can be primarily classified as multiple or single channel. The single-channel solution, investigated herein, is based on a switched antenna associated to a special Phase Locked Loop (PLL) receiver architecture that allows tracking the phase of each antenna. The PLL output is processed by a signal processing block that removes the ambiguity inherent to the PLL and estimates the angle of arrival of the source. This procedure is usually linked to high computational complexity that increases with the number of antennas and with the modulation level. This article proposes a technique to decrease the computational burden of the PLL-based single receiver DOA estimation scheme and to use the super resolution algorithm Multiple Emitter Location and Signal Parameter Estimation to obtain azimuth and zenith angles with improved accuracy. The simulated results using the novel algorithm are shown and its performance compared to the traditional solution in different scenarios.

Evaluation of a novel tubular sample holder for dielectric measurements with Abdulnour's method

This paper assesses the accuracy of a rectangular waveguide pierced by a tubular load sample holder for measuring liquid materials at high temperatures with a formulation based on Abdulnours method. The measurement technique is derived from the transmission line method. The sample holder is adapted from a section of a rectangular waveguide pierced by a tubular load for high temperature measurements at 2.45 GHz. Simulations of the loaded sample holder are carried out with CST Microwave Studio® for several values of sample permittivity. The accuracy of the technique is evaluated by comparing these values to those obtained from Abdulnours extraction model. It is shown that by properly choosing a set of calibration standards the technique can be quite accurate.