Orlandino Testa

An accurate UTD model for the analysis of complex indoor radio environments in microwave WLAN systems

An accurate uniform theory of diffraction (UTD) model for the analysis of complex indoor radio environments, in which microwave WLAN systems operate, is presented. The model employs a heuristic UTD coefficient suitable to take into account the effects of building floors, walls, windows, and the presence of metallic and penetrable furniture. A numerical tool based on an enhanced tridimensional beam-tracing algorithm, which includes diffraction phenomena, has been developed to compute the field distribution with a high degree of accuracy. After the validation of the model, obtained by means of some comparisons with measurements available in literature, an accurate electromagnetic characterization of typical indoor environments has been performed. The numerical results show that the electromagnetic field distribution and the channel performances are significantly influenced by the diffraction processes arising from the presence of furniture.

Design, Realization, and Test of a UWB Radar Sensor for Breath Activity Monitoring

An analytical model of an ultrawideband range gating radar is developed. The model is used for the system design of a radar for breath activity monitoring having sub-millimeter movement resolution and fulfilling the requirements of the Federal Communications Commission in terms of effective isotropic radiated power. The system study has allowed to define the requirements of the various radar subsystems that have been designed and realized by means of a low cost hybrid technology. The radar has been assembled and some performance factors, such as range and movement resolution, and the receiver conversion factor have been experimentally evaluated and compared with the model predictions. Finally, the radar has been tested for remote breath activity monitoring, showing recorded respiratory signals in very good agreement with those obtained by means of a conventional technique employing a piezoelectric belt.

A three-dimensional UTD heuristic diffraction coefficient for complex penetrable wedges

A three-dimensional heuristic diffraction coefficient, useful to predict the electromagnetic field scattered from penetrable wedges of complex geometry, is presented. The model, based on a modification of the exact uniform theory of diffraction (UTD) metallic wedge diffraction coefficient, allows the analysis of a large class of penetrable objects with an adequate degree of accuracy. Numerical results concerning the scattering from solid and hollow penetrable wedges show the suitability of the proposed diffraction coefficient to analyze complex structures of large practical interest. A good agreement with exact numerical results already available in the literature has been found.

A UTD/FDTD investigation on procedures to assess compliance of cellular base-station antennas with human-exposure limits in a realistic urban environment

In this paper, different exposure situations for a subject standing inside a room of a building with a window facing a rooftop-mounted base-station antenna are analyzed. The study is accomplished by using a technique combining the uniform asymptotic theory of diffraction and the finite-difference time-domain method, suitable to characterize human exposure in realistic urban environments at a reasonable computational cost. The different exposure conditions examined are analyzed to highlight the problems related to compliance assessment procedures in complex exposure scenarios and to suggest some possible solutions. A comparison of the results obtained in these scenarios with those computed neglecting the presence of the room walls (free-space situations) evidences that, under certain conditions, average exposure field levels and specific absorption rates (SARs) in the realistic environments can be higher than in free space, thus demonstrating that compliance assessment carried out in free space can yield nonconservative results. As concerns implications of field nonuniformities, typical of realistic urban environments, on SAR values, the results show that the whole-body averaged SAR is related to the average field value, provided the averaging procedure is appropriately chosen to cover all the volume occupied by the subject (V/sub S/) and not only a vertical surface. Local SAR values, instead, show a more complex relation with the exposure field, such that considering only the V/sub S/-averaged field value for compliance assessment might lead to an underestimation of the real exposure level, while using the peak of the field in V/sub S/ leads to a remarkable overestimation.

A Numerical Scheme for the Solution of the Vector Parabolic Equation Governing the Radio Wave Propagation in Straight and Curved Rectangular Tunnels

A high-frequency field prediction model, useful to evaluate the radio wave propagation in realistic tunnels having rectangular cross-section, is presented. The model is based on a hybrid implicit/explicit finite-difference numerical scheme adopted to solve the vector parabolic equation (VPE) governing the electromagnetic field propagation in straight and curved tunnels. To model the materials forming the tunnel walls, mixed Dirichlet-Von Neumann boundary conditions are employed. In this way, all the relevant field propagation processes are properly taken into account. To show the feasibility of the proposed numerical method, results concerning the spatial distribution of the electromagnetic field and the power flux in straight and curved rectangular tunnels are provided. An analysis concerning the convergence properties of the proposed numerical scheme is also reported.

A High-Gain Mushroom-Shaped Dielectric Resonator Antenna for Wideband Wireless Applications

A high-gain mushroom-shaped dielectric resonator (DR) antenna for wideband wireless applications, featuring 65% fractional bandwidth, is proposed. The antenna consists of a low-permittivity hollow cylindrical DR provided with a top-mount spherical cap lens and a metal reflector, excited by means of coaxial probes. Suitable shaping of lens and reflector yields high gain (exceeding 14 dBi) and limited back radiation. The proposed antenna features a broadside radiation diagram with stable radiation patterns and wideband impedance matching. Its potential applications include access points for indoor/outdoor wireless multimedia systems as well as satellite terminal receivers. CST Microwave Studio, implementing a full-wave locally conformal finite integration technique, is employed to design and characterize the antenna, while the singularity expansion method is adopted to express the antenna response to arbitrary excitation waveforms. The numerical results concerning the antenna parameters are found to be in good agreement with the experimental measurements performed on an antenna prototype.

Wideband and UWB Antennas for Wireless Applications: A Comprehensive Review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems.

A Numerical Procedure for the Analysis of EMC/EMI Problems in Radio Communication Systems Operating in Complex Environments

An efficient combined full-wave/high-frequency procedure useful to evaluate the spatial distribution of the electromagnetic field excited by radio sources operating in complex environments is presented. The procedure is based on a full-wave technique for the evaluation of the field distribution excited within a volume surrounding the radiating sources, and a dedicated high-frequency technique useful to model the propagation and interaction of the electromagnetic field with electrically penetrable objects forming the operative environment. In this way, it is possible to determine, with a reduced computational burden, the field distribution from the source location to the far-field region while keeping a high numerical accuracy. Using the proposed procedure, it is possible to evaluate the performance of mobile radio communication systems taking into account the impact of the operative environment, which is in turn essential to identify safety areas in compliance with the electromagnetic compatibility (EMC) regulations. Numerical examples aimed to predict potential EMC/EMI issues which could be caused by a mobile communication system operating in a complex scenario modeling a crisis area are also reported.

An electromagnetic characterization of indoor radio environment in microwave WLAN systems

An accurate electromagnetic characterization of a typical indoor environment in which a microwave WLAN system operates is presented. The characterization has been performed by means of a heuristic UTD diffraction coefficient suitable to take into account not only the effects of building walls, floors, and corners, but also the presence of penetrable furniture. The numerical results show that the electromagnetic field distribution and the channel performances are significantly influenced by the diffraction processes arising from the presence of furniture.

A UTD/FDTD model to evaluate human exposure to base-station antennas in realistic urban environments

A technique combining uniform asymptotic theory of diffraction and finite-difference time-domain (UTD/FDTD), suitable to characterize human exposure in realistic urban environments at a reasonable computational cost, is presented. The technique allows an accurate evaluation of field interaction with penetrable objects (walls, windows, furniture, etc.) and of power absorption in a high-resolution model of the exposed subject. The method has been applied to analyze the exposure of a subject standing behind a window in a building situated in front of a rooftop-mounted base-station antenna. A comparison of the obtained results with those computed neglecting the presence of the building (free-space condition) evidences that a realistic modeling of field propagation in the actual scenario is essential for an accurate evaluation of absorbed power distribution inside the human body.