Browsing by Author "Fernandes, Telmo R."
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- Characterization of wireless propagation through traditional Iberian brick wallsPublication . Ferreira, David; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.; Cuinas, InigoThis paper presents the wireless transmission properties for brick walls with different thicknesses and facade finish coatings. The ceramic hollowed bricks under study are traditionally employed in the Iberian residential construction, where the 11, 15 and 20 cm thicknesses are most common in indoor and outdoor walls. For each brick dimension, three different prototypes were manufactured varying in the type of wall finish, i.e.: naked brick, smooth painted plaster and rough painted plaster. The prototypes were measured in an anechoic chamber at frequencies ranging from 680MHz up to 10GHz. Results demonstrate that the brick wall internal heterogeneity, as well as the type of finish, significantly influence the frequency response of the walls.
- Dual‐band single‐layer quarter ring frequency selective surface for Wi‐Fi applicationsPublication . Ferreira, David; Cuiñas, Iñigo; Caldeirinha, Rafael; Fernandes, Telmo R.This study proposes a frequency selective surface (FSS) design to be used in Wi‐Fi shielding applications as either a band reject or band pass dual‐band single‐layer filter. The proposed design consists of a combination of basic elements, that is, ring loops/slots, and is tuned at both 2.4 and 5.2 GHz Wi‐Fi frequency bands. It has a relatively stable frequency response in the aforementioned Wi‐Fi bands for incidence angles ranging from 0° to 45°. Both band reject and band pass designs are presented, along with their unit cell dimensions. Simulation and model validation through measurements demonstrate the performance of the proposed FSS design. Active variants are also proposed and briefly evaluated, in simulation environment, which should allow for applications where an on–off switching is desired at 2.4 and 5.2 GHz Wi‐Fi bands.
- Enabling spatial diversity and beamsteering with reduced RF-chains using reconfigurable transmitarraysPublication . João R. Reis; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.; Hammoudeh, AkramThis manuscript introduces a new vision on the implementation of spatial diversity with beamsteering capability, by suppressing the typical beamforming networks of antenna phased arrays and replace them by Reconfigurable Transmitar- rays. Consequently, the radio frequency components, i.e. RF- chains that compose such systems, were replaced by a device with the capability to perform two-dimensional beamsteering relying on single antenna source, hence reducing the number of associated RF hardware in comparison with traditional phased array systems. By spatially distributing side-by-side more than one device, spatial diversity with beamsteering is enabled with an estimated reduction of 1:8 in the number of associated RF-chains. This new concept clearly demonstrates its merit by directly reducing the implementation costs„ RF-chain components and increasing the energy efficiency, specially in larger systems.
- Investigation of a Radio Propagation Model for Vegetation Scatter Dynamic Channels at BFWA FrequenciesPublication . Morgadinho, Sérgio; Richter, Juergen; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.The successful deployment of wireless technologies in the micro- and millimetre frequencies relies on the understanding of radio channel propagation and accurate radio propagation models. To this extent, the dynamic effects of vegetation on radio signals are investigated, as a function of wind direction, receiver location and vegetation depth. Furthermore, a radio propagation model, based on the RET, is investigated as an approach to predict the channel dynamic effects of vegetation scatter at 20 GHz. The model is evaluated for a structured forest medium, and its performance is assessed through the use of primary, secondary and error quantification statistics.
- Metamaterial-inspired Flat-Antenna Design for 5G Small-cell Base-Stations Operating at 3.6 GHzPublication . Reis, João R.; Fernandes, Telmo R.; Patrício Carreira Vala, Mário António; Caldeirinha, Rafael F. S.In this paper, a flat-beamsteering antenna for 5G applications is being presented. The antenna, designed to operate at 3.6 GHz (5G new radio (NR) frequency range 1 (FR1) band n78), presents a unique flat form factor which allows easy deployment and low visual impact in 5G dense scenarios. The antenna presents a multi-layer structure where a metamaterial inspired transmitarray enables the two-dimensional (2D) beamsteering, and an array of microstrip patch antennas is utilised as RF source. The use of metamaterials for beamsteering control allows for the reduction of costly and complex phase-shifter networks by using discrete capacitor diodes to control the transmission phase-shifting and subsequently, the direction of the steering. According to simulations, the proposed antenna presents 13.9 dBi of gain, 100 MHz of bandwidth with a maximum steering range of ±20 degrees, achievable in both elevation and azimuth planes, independently.
- Retrieving Vegetation Reradiation Patterns by Means of Artificial Neural NetworksPublication . Gomez-Perez, Paula; Caldeirinha, Rafael; Fernandes, Telmo R.; Cuinas, InigoModeling vegetation usually implies obtaining experimental data by means of measurement campaigns. In general, the most accurate models need the reradiation pattern of the vegetation volume under study, or some of its related parameters. Obtaining this function might not be easy, and the measurement procedure may introduce errors depending on the location of the vegetation mass. An accurate tool to simplify this process is presented, based on the ability of artificial neural networks to infer behavioral patterns. This proposal reduces the acquisition of the experimental data to a scarce set of angles around the tree or bush, which will then be used to train a neural network capable of retrieving the desired reradiation function desired.
- A Three-Dimensional Directive Antenna Pattern Interpolation MethodPublication . Leonor, Nuno R.; Caldeirinha, Rafael; Sanchez, Manuel Garcia; Fernandes, Telmo R.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 antenna's 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 Two-Dimensional Ray-Tracing-Based Model for Propagation Through Vegetation: A practical assessment using ornamental plants at 60 GHz. [Wireless Corner]Publication . Leonor, Nuno R.; Caldeirinha, Rafael F. S.; Garcia Sanchez, Manuel Garcia; Fernandes, Telmo R.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.