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Accurate radio wave prediction models are necessary for the innovation of mobile communication technology and the deployment of wireless sensor networks in railways. The parabolic wave equation (PWE) method is one commonly used method to predict the electromagnetic characteristic of long railway tunnels. However, the advent of novel antennas and technologies (e.g., beam steering, beamforming) has posed new challenges to PWE‐based models such as effective means of taking tilted beam patterns into account. This study addresses such a challenge by using tilted Gaussian beams to embed antennas with oriented patterns or tilted beam directions into PWE‐based models. The proposed approach does not reduce the simulation efficiency of PWE itself. The validity and practicability of the technique are demonstrated by comparing against ray‐tracing as well as experimental measurements in various tunnel environments. [ABSTRACT FROM AUTHOR]

On‐body propagation channels show significant polarization selectivity that has dominant impacts on the on‐body link quality in wireless body area networks. For on‐body relay channels over long distances across the body, the antenna polarization configurations of the relaying nodes are crucial to determine the relay performance, thereby requiring polarization optimization schemes. In this article, narrow band flat‐fading on‐body channels at 2.484 GHz are measured to analyse their polarization distribution above the skin under static postures. The measured on‐body channels show full‐space polarization convergence and dispersion, which are modelled by an extended 3 by 3 channel polarization matrix, and a statistical channel model is also proposed. Multi‐hop polarized on‐body relay channels are analysed on the relay link capacity, which shows polarization dependency between adjacent hop channels when relaying nodes are mounted by linearly polarized antennas. Both regular and iterative polarization selection algorithms are then designed to optimise the antenna polarization configuration of the nodes. Simulations based on the proposed polarization distribution model show significant link capacity increases for two‐hop and tfhree‐hop on‐body relay channels by the optimization algorithms. The results confirm the necessity of proper polarization selection schemes for on‐body relay channels. [ABSTRACT FROM AUTHOR]

In spherical near-field (NF) measurements, post-processing techniques based on spatial filtering have been presented as an interesting tool for the mitigation of echoes or stray signals deriving from the environment surrounding the antenna under test (AUT). The spatial filtering is very efficient in measurement scenarios with a stationary AUT. Whenever the AUT is rotating, in order to increase the effectiveness of the echo reduction, the antenna needs to be displaced outside the centre of rotation. Unfortunately, the number of acquisition samples needed to represent the AUT in offset configuration is higher with respect to one needed for the onset configuration. An innovative NF/far-field transformation algorithm for spherical offset measurements which allows to significantly reduce the number of measurement samples has been recently proposed. Such technique has been named translated spherical wave expansion (TSWE) and is based on the definition of new reference systems centred on the AUT rather than on the origin of the measurement sphere. In this study, the authors present the experimental investigation of the TSWE echo reduction properties for offset AUT. [ABSTRACT FROM AUTHOR]

The performance of the satellite communication systems employing polarisation diversity or frequency-reuse schemes to improve the spectral efficiency is degraded due to the depolarisation-induced interference originated by raindrops and ice particles present along the Earth-Space propagation path. Two models account for both rain and ice contributions. One predicts the long-term cumulative distribution function (CDF) of cross-polarisation discrimination (XPD). The other predicts the relationship between XPD and co-polar attenuation (CPA) and it was derived considering exclusively data at the V-band. In this study, the former model is improved by considering the individual ice and rain contributions and their combined effects, while the latter is validated against new measurements at the Ka band. New models are then proposed for the XPD-CPA relationships at the Ka-band taking into account both rain and ice contributions and also their combined effects. Finally, the predictions provided by the first model are usually converted to the corresponding XPD-CPA relationship using the long-term first-order statistics of rain attenuation, (incorrectly) considering that the equiprobability hypothesis applies. A new approach for the conversion of the XPD CDF into the corresponding XPD-CPA relationship is presented. [ABSTRACT FROM AUTHOR]

This contribution presents propagation measurements at 60 GHz in indoor non-line of sight scenarios. Besides analysing the measurements, the authors have considered several system aspects, such as bandwidth and directivity in order to investigate the small-scale behaviour of the radio channel after beam-forming. The results show that due to the high resolution in the angular and time domain achievable by large antenna arrays and wideband signals, the fading is significantly reduced and the equivalent transmission channel becomes more sparse and deterministic. These insights represent an essential source of information for future systems design and the ongoing channel modelling activities for systems operating at mm-waves. [ABSTRACT FROM AUTHOR]

This study presents an improved method of reactive loading for miniaturisation of coupled-line filters. Compared to the previous method, the proposed method requires a reduced number of reactive elements. Moreover, miniaturisation is accomplished with equal reactance. Effectively, this further decreases the number of reactive elements. Therefore apart from improved loss performance because of the reduced number of low-Q lumped elements, low-cost fabrication and simpler design procedure are also achieved while maintaining a similar rate of miniaturisation. A complete set of design equations is provided for both shunt-capacitive and series-inductive loading. The ideal simulation results, which are in excellent agreement with those of conventional counterparts based on λ/4 lines, theoretically validate the method, whereas the experimental results that match the ideal results better than the previous method demonstrate the practicality of the proposed method. [ABSTRACT FROM AUTHOR]

The tremendous growth of low power wireless technologies oriented to smart city applications has conduced to evaluate the propagation aspects under typical communication scenarios in urban environments where in contrast to cellular technologies the transmitter and or the receiver antenna can be deployed at different heights near ground. Thus, the authors introduce a unified empiric parametrised propagation model with validated parameters from the measurements to study the propagation characteristics in near-ground scenarios. The proposed model considers the antenna's height as well as external power losses because of objects that may block the line-of-sight to the receiver. The main results of this research demonstrate that in near-ground wireless links, the wireless range is severely reduced because of diffraction caused by ground. However, in scenarios where the receiver is always higher than the transmitter the diffraction is null and the path loss slope is less than free space, with the consequence of a considerably higher wireless range. The propagation model presented here is a valuable tool for network planning where typical cellular propagation models might not be appropriate. [ABSTRACT FROM AUTHOR]