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For the last decades satellite communication systems have been moving towards higher and higher frequencies; rain attenuation along the Earth-satellite path can be an important limiting factor for the system availability, especially in tropical regions where rain events can be particularly intense. One of the possible countermeasures is site diversity. In this paper we evaluate the performance of...
The objective of this paper is to present the development of a new software tool for the analysis of propagation effects on satellite-to-aircraft communications, valid for frequencies between VHF and Ka-band. This tool shall take into account several phenomena that influence the characteristics of the propagation channel, and therefore the performances of the link. First of all, the antenna pattern...
In this work, we do an empirical approach to identify 802.11n technology Train to Ground communication specifics in underground applications from an industrial point of view. The equipment for the measurements was located aboard and along a track. The experiments consisted on measuring signal to noise ratio levels and beacon loss along a standard train cycle for physical layer performance assessment...
As increased requirements for much high speed and capacity in wireless communications, frequency bands become higher, such as millimeter wave or terahertz wave. In these high frequency bands, beamforming is employed to gain stable connectivity. On-body body area network is one of fascinate application of these high capacity frequency bands. However, directions of on-body antennas largely varies and...
With the advent of the Internet of Things, body-worn sensor nodes are continuously becoming more important. In case of bio-medical, rescue-worker or military applications sensitive data are often transmitted, requiring the need for encryption. The distribution of symmetric encryption keys is often an issue leading to security risks. Body-worn sensor nodes are generally employed in quickly varying...
The position of radiative Wireless Power Transfer (WPT) in the spectrum of power harvesting is given and a brief history of radiative WPT, starting with the work of Faraday is presented. The challenges in increasing the received dc power level or the transfer distance are outlined and possible directions for a solution are indicated.
In this paper the main challenges that far field wireless power transmission should deal with will be presented and discussed. New developments made in Aveiro University in order to solve some of the issues raised will also be discussed, those include the use of special design waveforms, special design of antennas for WPT and also alternatives for WPT RF-DC conversion efficiency.
We present a general methodology to arbitrarily manipulate the amplitude and phase of an electromagnetic wave propagating in a two-dimensional medium, without introducing any scattering. This leads to a class of isotropic spatially varying permittivity and permeability profiles that are transparent to an incident plane wave while shaping the field magnitude. Furthermore, we propose a metamaterial...
Wave propagation in a general dispersive chiral media is examined by a novel finite difference time domain (FDTD) technique. Using convolutional integrals directly in time domain without use of transformation techniques such as Z-and Mobius transformations, wave field decomposition is the main idea to drive the FDTD formulation. Time domain permittivity, permeability, and chirality of dispersive materials...
Railway transportation is increasing very fast in all countries, and as a consequence new railways demand high quality communications for control and signaling of trains, as well as high capacity communications for passengers. However, current communications systems cannot provide these services, so 5G systems will be needed to replace old GSM-R and dedicated systems for railway signaling. Also, 5G...
This paper considers a liver implanted antenna and its associated radio telemetric channel using ultra wideband (UWB) technology. The performance of both the implant antenna and the radio channel is evaluated numerically and experimentally using human equivalent multilayer phantom to obtain S-parameter results within the 4–8 GHz band for various distances between the implanted antenna and a body-worn...
The augmenting need for remote monitoring and treating patients by biophysical sensors interconnected via Body Area Networks (BAN) has recently called researchers' attention. The private and confidential transferred data in such application require high information security. One of the solutions is to use human body as a transmission channel. The body surface-confined transmission restricts the off-body...
Based on Vector Network Analyzer (VNA) Measurements, a model for the specular reflection behavior of printed circuit boards (PCB) in the Terahertz range has been derived. It has been calibrated to suit the behavior of the measurements using a simulated annealing algorithm. The model has been tailored for integration to ray-tracing based propagation modeling.
The use of an array antenna, transmitting pulsed signals and applying time-delays between the elements to create an area of high power density in front of the array at a prescribed position at a chosen moment in time is discussed. Using realistic bandwidths and pulse repetition frequencies leads to the creation of undesirable hot spots. Replacing the array elements with small phased array antennas...
A concept of a beam-steerable radiator based on a reconfigurable cavity antenna and coupling elements is proposed in this paper. The coupling elements are designed as magnetic dipoles which are realized using half-mode substrate-integrated cavities. Thus, the antenna exhibits vertical polarization in a planar structure. The main beam can be switched among different directions towards end-fire. Furthermore,...
A new calibration method of active phased array antennas is presented in this paper. This method can be applied to the antenna arrays of various sizes and various radiating element numbers. It takes into account the edge effects and the coupling between the radiating elements. This method allows avoiding the degradations of the antenna radiation pattern caused by mismatch produced during a scanning...
For modelling the propagation of electromagnetic waves in the low troposphere, the discrete mixed Fourier method is classically used. It is based on a finite-difference approximation of the ground boundary condition. However, the propagator of the split-step Fourier method is derived from continuous equations. In this paper, we apply the finite-difference approximation to the propagation equation...
Recently, contactless landslides prognostication systems using light wave lasers and ultrasonic waves have been researched and developed, but they suffer from deterioration of detection accuracy due to environment resistance. To overcome such difficulty, electromagnetic waves have been focused on, and a system which can detect water contents in hydrated soil by electromagnetic waves has been investigated...
This contribution reports the results of a large broad band measurement campaign on the frequency response of radio channels at 5.8 GHz band. Up to five scenarios, in both line of sight and obstructed line of sight, configure the testbed of this work. After gathering data along linear paths, Doppler Effect principles allow the estimation of the angle of arrival of any multipath contribution. The analysis...
The upcoming migration of satellite services to higher bands, namely the Ka- and Q-bands offers many advantages in terms of bandwidth, data rates and system capacity. However, it poses challenges as propagation effects introduced by the various atmospheric phenomena are particularly pronounced in these bands and can become a serious constraint in terms of system reliability and performance. This paper...
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