Percorrer por autor "Fernandes, T."
A mostrar 1 - 3 de 3
Resultados por página
Opções de ordenação
- Modelling and measurements of the directional spectra of scatter signals inside a formation of tree trunksPublication . Leonor, N.; Caldeirinha, R.; Fernandes, T.; Ferreira, D.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.
- On the applicability of the dRET model to the trunk layerPublication . Fernandes, T.; Leonor, N.; Caldeirinha, R.; Richter, J.; Al-Nuaimi, M.This paper presents a method to model the scattered signal from a regular formation of cylinders, both dielectric and metallic, at micro and millimeter wave frequencies. The model, aims to predict the signal emanated inside and around an isolated block of tree trunks, and might be used as part of a larger algorithm intended to model isolated volumes of vegetation. The method presented here, is based on the prior knowledge of the re-radiation function of cylinders and used the dRET (discrete Radiative Energy Transfer) model, to gather the interactions between the trunks present in the formation to predict the directional profile of the received signal power level at various location inside the formation. The re-radiation function from cylinders, is predicted based on a model previously applied to lamp posts, and is assessed by comparison with measurements performed at 18 and 36 GHz. These functions are subsequently used to input the dRET model whose predictions were also assessed with measurements obtained inside an anechoic chamber, using the same spot frequencies.
- Two-dimensional antenna beamsteering using metamaterial transmitarrayPublication . Reis, J. R.; Al-Daher, Zaid Al-Daher; Copner, Nigel Copner; Caldeirinha, R. F. S.; Fernandes, T.A new two-dimensional (2D) beamsteering antenna technique using a metamaterial transmitarray structure is proposed in this paper. The proposed technique allows the steering of the main lobe of the original antenna pattern in both elevation and azimuth planes when coupled to a conventional horn antenna. This has been demonstrated on a 5 × 5 unit-cell stacked structure, in which electromagnetic simulations, performed at 5.35 GHz, allowed the evaluation of the unit-cell parameters and the behaviour of the array. A fixed steering output with range of θ = 25° and φ= 25° in spherical coordinates is achieved by means of electromagnetic simulations and validated against experimental results, clearly demonstrating the potential of using metamaterials structures for beamsteering purposes.