Renato Cicchetti

Response of a planar microstrip line excited by an external electromagnetic field

The voltages and currents induced by external electromagnetic fields on a planar microstrip line have been studied with the use of a distributed-source transmission-line model. The frequency response of the microstrip line has been analyzed by simulating the illuminating field with a plane wave arbitrarily incident on the line. The influence of the microstrip geometrical and electrical characteristics on the voltages and currents induced on the line has been examined, and indications for reducing the circuit susceptibility have been obtained. The model adopted can be used for studying the response of the line to any type of external field arbitrarily varying in space time. Numerical results show that for lines loaded with the characteristic impedance at both terminals, voltage amplitudes on the order of some millivolts and currents of some hundreds of microamperes can be induced at f=3 GHz by an incident plane wave with an electric-field intensity of 1 V/m and for various angles of incidence. The voltages and currents induced on a microstrip circuit can be reduced by using substrates of sufficiently high permittivity. >

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.

Estimation of the peak power density in the vicinity of cellular and radio base station antennas

Prediction formulae for estimating the peak equivalent power density in the near-field of cellular base-station array antennas are demonstrated. Theoretical justification stemming from a uniform asymptotic expansion of the field radiated by collinear arrays is described, and verification is carried out by means of an extensive computational analysis of different classes of base station antennas. The formulae, which depend on a few, readily available parameters, can be conveniently employed for the estimation of compliance distances with respect to RF safety guidelines issued by the International Committee on Non-Ionizing Radiation Protection (ICNIRP), which have been adopted in many countries throughout the world, without requiring necessarily extensive and expensive nearfield measurements campaigns.

An efficient RF exposure system with precise whole-body average SAR determination for in vivo animal studies at 900 MHz

A radial electromagnetic cavity has been designed and optimized for the in vivo whole-body exposure of mice to 900-MHz RF fields. Parallel circular plates shorted around the perimeter form the cavity, which is fed at the center in order to excite a cylindrical TEM wave. Plastic housings allow the insertion and equidistant positioning from the exciter of 40 mice, with the electric field parallel to the body axis. The resulting exposure system is highly efficient, featuring more than 80% of the incident power dissipated in the mice. The whole-body average SAR can be determined with remarkable precision by means of straightforward power balance since the RF power leakage from the cavity is extremely low. Fairly uniform exposure of the mice, individually and collectively, has been achieved by means of the symmetric arrangement. This exposure system has been adopted in a replication study on transgenic mice currently being carried out in South Australia, and is being considered for upcoming animal studies in Europe.

A Low-Profile Printed Drop-Shaped Dipole Antenna for Wide-Band Wireless Applications

A class of printed antipodal drop-shaped dipole antennas for wideband wireless communication systems is presented. A suitable shaping of the feeding lines and radiating arms is adopted to achieve an operating bandwidth larger than 10 GHz useful to meet the requirements of several wireless communication standards. A thin, low permittivity dielectric substrate is used to reduce the excitation of surface waves which are responsible for a degradation of the radiative characteristics. The proposed antenna structures present a reduced occupation volume which allows an easy integration in mobile terminals, as well as in radio base stations. A locally conformal FDTD numerical procedure has been adopted to analyze the radiating structures. An equivalent circuit, useful to predict the frequency-domain behavior of the scattering parameters of a two-element array formed by the proposed structures, is also presented. The numerical results concerning the antenna parameters are found to be in good agreement with the experimental measurements.

Transient response of a microstrip line circuit excited by an external electromagnetic source

The transient voltages and currents induced by an external electromagnetic field along a microstrip line interconnecting active and/or passive components are studied by using a distributed-source transmission-line model. The influence of the angle of incidence as well as that of the microstrip geometrical and electrical parameters on the line response is analyzed. The instantaneous voltage and power induced on the loads by various types of pulse excitations are computed. Numerical results are obtained both for dispersive and nondispersive lines. A line feeding a transistor microwave amplifier is also considered. The results show the effects of the multiple reflections of the field inside the dielectric substrate and of the signal at the ends of the line. Indications of how to reduce the coupling between the external field and the considered structure are given. >

A full-wave analysis of interdigital capacitors for planar integrated circuits

A finite-difference time-domain (FDTD) model has been developed to determine the circuital and electromagnetic compatibility performances of a large class of interdigital capacitors (IDCs). The model, based on a new conformal FDTD scheme, employs the free-space dyadic Greens functions to analyze the field behavior near and far from the FDTD computational domain. Using the proposed model, various IDC structures have been analyzed and a frequency-independent equivalent circuit, which include surface and volume wave effects, has been introduced. A good agreement with numerical results already available in literature has been found.

A perturbed E-shaped patch antenna for wideband WLAN applications

A wideband E-shaped microstrip patch antenna for wireless communications is presented. Zig-zag slots and perturbations of the E-shaped metallic patch are employed to excite two resonant modes and achieve a wide-band frequency behavior, featuring a fractional bandwidth of about 30%, and, at the same time, to meet the occupation volume requirements of mobile wireless local-area network enabled communication devices. A locally conformal finite-difference time-domain numerical procedure has been employed to analyze the radiating structure. Numerical results concerning the antenna parameters are in good agreement with experimental measurements.

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.