Nuno R. Leonor

A 2D Ray-Tracing Based Model for Micro- and Millimeter-Wave Propagation Through Vegetation

A novel two dimensional model to characterize the electromagnetic behavior of trees has been developed with the purpose of being used in ray-tracing based simulation platforms. This model uses various point scatterers with specific radiation characteristics to describe the effect of the trees present in the radiowave propagation path. The method to extract the parameters of the point scatterers from measurements is presented. The performance of this novel formulation is assessed in a tree formation scenario against measurements results obtained in a controlled environment, inside an anechoic chamber, at 20 and 62.4 GHz. Additionally, a comparison analysis with a discretized radiative energy transfer (dRET) approach is conducted, where a relatively good agreement has been found. The absence of readily plug-in models considering propagation through and/or around vegetation makes this new tool interesting for radio planning purposes.

A Simple Model for Average Reradiation Patterns of Single Trees Based on Weighted Regression at 60 GHz

Due to their complex and inhomogeneous characteristics, the propagation and radiation parameters of trees and vegetation areas are very difficult and time consuming to obtain. This communication proposes a statistical method, using robust weighted local regression, to minimize the influence of the effect of the tree inhomogeneity on its reradiation pattern, allowing the evaluation of averaged reradiation functions from simple measurements. The proposed method was successfully applied to six tree specimens of both conifer and ficus species, at 60 GHz. Furthermore, once this empirical averaged function is obtained, first-order statistics can be applied to generate several simple reradiation functions, statistically identical to those obtained from measurements. Thus, allowing the full characterization of the tree under study.

Extension of the dRET Model to Include Scattering from Tree Trunks in Microcell Urban Mobile Scenarios

This paper proposes a framework for extending the applicability of the discrete RET (dRET) model to accommodate radiowave scattering from tree trunks, particularly in microcell urban mobile scenarios, at micro- and millimetre wave frequencies. This framework aims to provide accurate modelling of the signal emanated inside and around isolated blocks of tree trunks, for instances, in raised canopy forests or in urban street canyons like scenarios. Model validation against measurement results inside an anechoic chamber for a double line of regularly spaced metallic and dielectric trunks at 18.8 GHz, as well as recommendations for a more encompassing model, are presented.

Estimation of dielectric concrete properties from power measurements at 18.7 and 60 GHz

In this paper, microwave and millimetre wave reflection coefficient measurements at 18.7 and 60 GHz are presented for a group of concrete slabs, in which only the thickness of the gravel present inside is varied. An empirical reflection coefficient value is determined using both reflected and LOS power measurements. A concrete slab with no gravel is used as a reference. The measurement results show the dependence of the reflection coefficient with the thickness of the gravel inside the slab. The measurement results allow for the appropriate extraction of dielectric properties of the materials under study.

A Two-Dimensional Ray-Tracing-Based Model for Propagation Through Vegetation: A practical assessment using ornamental plants at 60 GHz. [Wireless Corner]

This article aims to practically assess the point scatterer formulation to characterize the electromagnetic behavior of ornamental plants with varying thickness at 60 GHz. The proposed propagation model uses various point scatterers with specific radiation characteristics, distributed within a computational area, to describe the effect of the plants present in the radiowave propagation path. Additionally, a ray-tracing-based engine is used to gather all the interactions between the point scatterers present in the simulation channel. The performance of the proposed modeling approach is assessed against reradiation measurements of single and isolated plants, performed in the 60-GHz frequency band, inside an anechoic chamber. Additional model validation is obtained from reradiation measurements of several clumps of plants, mimicking specimens with varying thickness.

Extension of the dRET Model to Forests of Thin Cylinders

This 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 raised canopy forests

This paper presents a feasibility study on the extension of the point scatterer formulation to characterise the electromagnetic behaviour of tree trunk formations. The original propagation model, successfully used in the canopy layer, 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. Subsequently, a ray-tracing based algorithm is used to gather all the interactions between the different point scatterers present in the simulation channel. This propagation model is now extended and applied to the trunk layer. To this extent, re-radiation measurements of both metallic and dielectric cylinders were performed in a controlled environment, inside an anechoic chamber, at 9.4, 18.8 and 37.6 GHz, were used to assess the model performance when dealing with single and isolated tree trunks. The proposed propagation model was then assessed against directional spectra measurements conducted within tree trunk formation scenarios at 9.4, 18.8 and 37.6 GHz. Additionally, a comparison analysis with a discretised radiative energy transfer (dRET) approach is conducted, where a relatively good agreement has been found.

A Three-Dimensional Directive Antenna Pattern Interpolation Method

An interpolation method to reconstruct the 3-D directive antenna pattern is presented. The proposed method is based on the prior knowledge of the original antennas principal planes patterns, to which a specific weighting method is applied to obtain an approximate 3-D antenna pattern. The performance of the proposed interpolation method is evaluated against 3-D antenna patterns from three typical directional antennas, extracted from appropriate electromagnetic simulation. Finally, a comparative analysis between the proposed method and current interpolation methods present in the literature is presented.

A simple scattering model for tree trunks

This paper presents the work carried out in an effort of modelling the scattering and absorption effects of single tree trunks with application to the discrete Radiative Energy Transfer (dRET) based model applications. The assessment of the proposed empirical model was performed against measurements of both metallic and dielectric cylinders, mimicking tree trunks, at several micro- and millimetre wave frequencies, i.e. 9.4, 18.8 and 37.6 GHz. These were carried out in a controlled environment, i.e. an anechoic chamber, so that frequency dependent effects could be evaluated.

Modelling and measurements of the directional spectra of scatter signals inside a formation of tree trunks

This article proposes a method to predict the scattered signal inside and around a tree trunk formation. The method presented here is based on an empirical model that characterises the re-radiation patterns of both dielectric and metallic cylinders for three spot frequencies, 9.4, 18.8 and 37.6 GHz and, resorting to dRET (discrete Radiative Energy Transfer) model to gather all the interaction between trunks within a formation, the received signal can be predicted. Presented empirical model was developed based on both dielectric and metallic re-radiation pattern measurements in an anechoic chamber and it is used as an input parameter of dRET model, characterising the trunk cells. This paper also contemplates measurements within a tree trunk formation in order to assess the values extracted from dRET model.