Percorrer por autor "Al-Nuaimi, Miqdad O."
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- Depolarisation studies of single trees at 20 GHzPublication . Caldeirinha, Rafael F.S.; Al-Nuaimi, Miqdad O.This paper addresses the characterization of the polarization states of the re-radiated signal from a natural tree performed in the vicinity around deep signal fades, at 20 GHz. The polarization pattern method has been used to investigate the effects of depolarization and to further characterize the changes in the polarization state of the re-radiated signal occurring as a result of the currents induced in the trunk, branches and leaves, which are significantly influenced by the complex permittivities of the various materials making up the tree. Results presented in the paper will explain the signal behavior observed in the various regions around the tree. The results also show that depolarization, in addition to absorption and scatter, is an important factor formulating accurate models for propagation in vegetation.
- Microwave Propagation Modeling and Measurement of Scattering and Absorption Inside a Canopy Using the FDTD TechniquePublication . Caldeirinha, Rafael F. S.; Al-Nuaimi, Miqdad O.This paper proposes a novel method aimed at modeling microwave scattering and absorption inside a canopy, arising from the interaction with the individual components of the vegetation specimen, starting from primary models for leaves, trunk and branches. The method is based on the finite-difference time-domain (FDTD) technique to predict the 3-dimensional re-radiation fields of the entire tree, by combining the effects of the single elements forming the tree. Appropriate measurements performed in an anechoic chamber environment at microwave frequencies, i.e. 20 GHz, and in the forward scattering region, provided both model validation and a deeper insight into the problem. The model is shown to be capable of predicting the near-field radiated signal and the radar cross section (RCS). The predictions yielded good agreement with measurements and provides a good basis for a planning model capable of accounting for single trees in the radio path.
- Simplified RET model derived from path loss and directional spectrum measurements in vegetation media at 11.2 and 20 GHzPublication . Caldeirinha, Rafael F. S.; Fernandes, Telmo; Richter, Jürgen; Al-Nuaimi, Miqdad O.This study presents a simplified radiative energy transfer (RET) model derived from path loss and directional spectrum measurements in vegetation media at 11 and 20 GHz. Thus, a simplified extraction procedure for the inputs parameters based on the method foreseen by the international telecommunications union - recommendation (ITU-R) P.833-8, however for isolated vegetation volumes, is proposed. Results for specific measurements aimed at the extraction of the RET model parameters are subsequently presented and discussed. The extraction method relies on a limited set of propagation measurements to find and optimise the RET input parameters. Specific measurements of the received signal directional profile are used to show the applicability of the method. This parameter evaluation method is tested and assessed based on the received signal directional profile measurements performed in Populous trees at 11.2 and 20 GHz.
- Time-Variant Radio Channel Characterization and Modelling of Vegetation Media at Millimeter-Wave FrequencyPublication . Morgadinho, Sérgio; Caldeirinha, Rafael F. S.; Al-Nuaimi, Miqdad O.; Cuinas, Iñigo; Sanchez, Manuel Garcia; Fernandes, Telmo R.; Richter, JürgenResults of an extensive measurement campaign to characterize and model dynamic effects on the radio channel in vegetation media at 40 GHz, are presented. Using two small trees in an anechoic chamber, narrowband fast-fading measurements, utilizing co-polarized signals, were conducted to obtain radio channel characterization. This was performed as a function of the bi-static scattering angle, wind speed, wind incidence, and tree species. Furthermore, a modelling methodology is investigated and assessed as to its feasibility as a means to model vegetation dynamics effects on propagation. A radio channel model based on a simplified set of Markovian parameters, is proposed. The model is representative of the radio signal in the three main identified propagation regions around a vegetation volume as a mean to satisfactorily model highly time-variant radio signals. The propagation regions considered are receiver angular sections (in the azimuth plane) around the tree, where the received signal behaves distinctly for each region. Model validation results are presented using one of the tree species.