Browsing by Author "Leonor, Nuno"
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- Comparative Study of Computational Electromagnetics Applied to Radiowave Propagation in WildfiresPublication . Faria, Stefânia; Vala, Mário; Coimbra, Pedro; Felício, João; Leonor, Nuno; Fernandes, Carlos; Salema, Carlos; Caldeirinha, RafaelIn this paper, a comparative study of four computational electromagnetic techniques to model the 2-dimensional radiowave propagation phenomena in wildfires, is proposed. The fire dynamics for a small tree specimen is studied, in which gases released from the combustion process are used to investigate the generation of an ionised plasma and, thus, to evaluate the gradient of the medium refractive index using the cold plasma model. Consequently, the presence of fire has been demonstrated to introduce additional losses in the radio path that may be critical to radio communication systems that are widely used in mission critical applications. The gradient of the refractive index across the vegetation volume yielded by the cold plasma model is used as input parameter to different numerical methods and electromagnetic solvers at 385 MHz (i.e. TETRA frequency band in Portugal) and, subsequently, their applicability to wildfires is assessed.
- Disruptive Future of Radar Based on All-Digital PN Signal ProcessingPublication . Ribeiro, Carlos; Ferreira Gil, João; Caldeirinha, Rafael; Reis, Joao R.; Sardo, Andre; Duarte, Luis; Leonor, NunoThis paper presents the first results on the design and implementation of a real-time and high resolution monostatic radar at 24 GHz, based on the sliding correlation of pseudonoise (PN) sequences. The real-time radar, with a high time resolution better than 4ns, is used for moving target identification (MTI) in the presence of highly dense clutter, under harsh environments and severe weather conditions (fog, snow and fire smoke or plume). A radar signal processing based on alldigital PN sequences is proposed, which represents a quantum leap in radar future front-end architecture. Results obtained in a controlled environment, inside an anechoic chamber, are presented and a benchmark with a commercially-of-the-shelf solution is presented. © 2019 IEEE.
- Extension of the dRET Model to Forests of Thin CylindersPublication . Leonor, Nuno; Ferreira, David; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Manuel Garcia SanchezThis paper presents a feasibility study on extending the applicability of the discrete radiative energy transfer (dRET) model to the trunk layer of raised canopy forests. The framework herein presented, proposes a method to predict the scattered signal inside and around a formation of cylinders (mimicking thin tree trunks), which is based on the prior knowledge of the cylinder 2-D reradiation pattern as input parameters to the dRET model. The characterization and modeling of the cylinder 2-D reradiation patterns were performed in an anechoic chamber, so that frequency-dependent effects could be evaluated. The assessment of the proposed method was performed against measurements within a formation of both metallic and dielectric cylinders mimicking thin tree trunks, at micro- and millimeter-wave frequencies, i.e., 9.4, 18.8, and 37.6 GHz.
- A feasibility study on the extension of the point scatterer formulation to vegetation mediaPublication . Leonor, Nuno; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Sanchez, ManuelThis paper aims at the development of a novel ray-tracing based method to characterise and model the electromagnetic behaviour of trees and vegetation volumes. This model uses various point scatterers with specific radiation characteristics, distributed within a computational volume, to describe the effect of the trees present in the radiowave propagation path. Additionally, the method to extract the parameters of the point scatterers from measurements is presented. The performance of this novel formulation was assessed in a tree formation scenario against measurements results obtained in a controlled environment, inside an anechoic chamber, at both 20 and 62.4 GHz.
- A Framework for the Analysis of Wildfire Effects in Emergency Communication SystemsPublication . Leonor, Nuno; Fernandes, Carlos A.; Salema, Carlos; Caldeirinha, RafaelThis paper aims at the development of a simulation framework to enhance the quality, performance and the resilience of the emergency radio communication systems during a wildfire event. To this extent, this research work includes several studies that will contribute for the better understanding of the propagation effects on radio signals under fire environments, the development of a fire-front building up model, the development of a radio propagation tool to obtain coverage maps based on relevant models for propagation in rural areas, particularly in highly dense forest areas, taking into account the topography and clutter in the radio path and the integration of wildfire build up models into the radio propagation tool for an all encompassing radio coverage tool to aid ground forces in realtime with identification of radio exclusion zones in real-time as fire-front develops.
- STDCC radar at 24 GHz: first measurement trialsPublication . Ferreira Sardo, Andre; Reis, João R.; Duarte, Luis; Leonor, Nuno; Ribeiro, Carlos; Caldeirinha, Rafael F. S.This paper presents the first measurement trials for performance assessment of a real-time and high resolution monostatic radar operating at 24 GHz. The proposed real-time radar, which operates based on the sliding correlation of pseudo-noise (PN) sequences, provides a high time resolution better than 4 ns, useful for moving target identification (MTI) in the presence of highly dense clutter, under harsh environments and severe weather conditions (fog, snow and fire smoke or plume). The STDCC radar target detection capability is demonstrated in this paper, by measuring and identifying the radar data for 4 distinct scenarios, composed of multiple targets (up to 8), inside an anechoic chamber, demonstrating the potential of the proposed radar architecture.