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The aim of this paper is the development of a theoretical model of medium-voltage (MV) cables in the frequency range of 25-200 kHz, which can be easily implemented in the Simulink enviroment. Two transmission-line configurations: 1) line-ground and 2) line-line were considered. The model requires the knowledge of the transmission channel parameters in the frequency domain. Thus, a characterization of MV cables in the two transmission-line configurations by means of experimental measurements was performed on commonly used MV cables, RG7H1R, of different sections, 95 [mm.sup.2] and 185 [mm.sup.2] with an aluminum core and copper shielded. To validate the model, a comparison between the attenuation constant [alpha] measured and the one simulated for both configurations under study was carried out. Index Terms--Attenuation constant, medium-voltage (MV) cables, power-line communication (PLC), transmission line.

Some basic rules and values to include the attenuation effect of terrain obstacles in the medium wave (MW) band are presented. The analysis applies to ground wave propagated signals and focuses on the new digital broadcasting systems (HD-RADIO/IBOC and DRM) that require accurate predictions for appropriate network planning. This study is based on field strength data from a measurement campaign and the results represent a complementary approach to numerical solutions for planning purposes. A simple but efficient classification of the terrain prominences is presented and attenuation curves are calculated. Index Terms--Channel characterization, digital radio, ground wave, irregular terrain, prediction methods.

A two-port ring resonator is used to characterize the microwave properties of a microstrip line printed on Ferro A6-S low-temperature co-fired ceramic. The ring and its coupling gaps are simulated using a simple lumped-element model. The coupling gaps are modeled as capacitors, the values of which are extracted using a commercial two-and-one-half-dimensional electromagnetic simulator. The validity of the lumped-element model is assessed by comparing the simulated and experimental resonant frequencies and, for the first time, the simulated magnitudes of both the reflection and transmission coefficients are also compared with those obtained experimentally. A correction for the frequency pushing due to the capacitive loading of the coupling gaps is also presented. The resulting model is then shown to predict the resonant frequencies to within 0.11% from 5 to 40 GHz. The simulated and experimental reflection magnitudes are within 0.5 dB across the band, whereas the transmission magnitudes are within 3.5 dB up to 22 GHz. Experimental results indicate that the loss of the microstrip ranges from approximately 0.11 to 0.42 dB/cm across the band and that the relative permittivity of the substrate is nearly constant versus frequency with an average value of 6.17. Index Terms--Attenuation and permittivity measurements, equivalent lumped elements, resonant frequency, ring resonator.

This paper describes and rigorously validates single- and multiple-layer models of microstrip conductor loss appropriate for high-accuracy application in electromagnetic analysis software. The models are validated by comparison with measurement and by comparison with converged results. It is shown that in some cases an extremely small cell size is needed in order to achieve convergence. Several effects that make a significant contribution to loss and are not modeled by the classic square root of frequency loss model are investigated including dispersion and current on the side of transmission lines. Finally, the counterintuitive result that there is an optimum metal thickness for minimum planar conductor loss is explored. Index Terms--Conductivity, dispersion, electromagnetic, high frequency, loss, microstrip, microwave, resistance, skin effect, stripline, surface impedance.

The work reported herein empirically derived the coefficients of the power-law relation between the specific attenuation Y and each of two other quantities: the radar reflectivity factor Z and the rainfall rate R. The derivation was accomplished using raindrop size distributions (DSDs) measured in Montreal and Toronto using the precipitation occurrence sensor system (POSS) and a Joss-Waldvogel disdrometer (JWD). The specific attenuation was calculated for both spherical and oblate spheroidal raindrops. Prior to doing so, the effects of inaccuracies in small drop detection by the two systems on the resulting Y-Z and Y-R relations were examined. In computing the relations, the influence of grouping the DSDs according to the corresponding values of Z was assessed. The results from the two sites were then combined in a regression analysis to determine the coefficients of the power-law expressions. The final expressions were used to calculate the probability distribution of rain attenuation over several path lengths at 30 GHz. Conclusions that can be drawn from this work include that i) the uncertainties in the measurements of small drops do not appear to be critical to the derived relations for some frequencies considered in this work, ii) in computing rain attenuation estimates from radar reflectivity factors, different criteria for grouping the reflectivity factor measurements can be adopted without changing the statistics of the corresponding attenuation estimates, iii) differences, which are the smallest for frequencies around 20-30 GHz, are observed in the coefficients derived from the measured DSDs compared with those recommended by the ITU-R, and iv) the attenuation statistics at 30 GHz computed by applying the Y-Z power-law expression are resistant to spatial averaging. Index Terms--Radio propagation meterological factors, rain.

It was previously shown that the number of array elements must exceed the number of sources for subspace-based directional-of-arrival (DOA) estimation. This is clearly not practical for a direct-sequence code-division multiple access (DS-CDMA) wireless system since the number of mobile users is very large. To overcome the restriction, a DOA's estimator employing the code-matched filters and parallel MUSIC algorithms is proposed. In the asynchronous DS-CDMA system, we show that the multiple access interference (MAI) throughout the code-matched filter tends toward the real Gaussian distribution with zero mean. In addition, based on the singular value decomposition (SVD) of a finite amount of data, we achieve a theoretical expression for the mean-squared error (MSE) of the DOA's estimation. With the advantage of code-matched filter inherent in the DS-CDMA system, we prove that the proposed technique can obtain an unbiased DOA estimation with low MSE, even in the environment where the number of mobile users far exceeds the number of array elements. Simulation results verify the theoretical derivation. Index Terms--Direction of arrival estimation, multiaccess communication, singular value decomposition.

The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters [epsilon] and [sigma] of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented. Index Terms--Materials parameters, measurements, modeling and simulation, RF propagation, RF system engineering.

A revised worldwide method has been recommended by the Radiocommunications Sector of the International Telecommunication Union (ITU-R) in Recommendation ITU-R 530-8 for predicting the deep-fading distribution due to multipath propagation in the average worst month on VHF-EHF terrestrial line-of-sight links. This paper presents detailed testing results for the revised method on a 239-link data base from 22 countries around the world in comparison with results for the leading regional methods still frequently used by some link designers for worldwide applications (viz., the Barnett-Vigants method of the United States and the Morita method of Japan). An evaluation of the form of the prediction equation is given for the revised and previous ITU-R methods and several regional methods. The revised ITU-R method is shown to perform significantly better than the other methods for both overland and coastal/overwater links. Index Terms--Fading channels, microwave radio propagation, multipath channels, prediction methods, radio repeaters.

The ITALSAT propagation experiment, started in early 1991 and still on-going, allows an extensive program of measurements at 18.7, 39.6, and 49.5 GHz. This paper reports the results obtained so far from copolar signal measurements carried out at the Earth station of Spino d'Adda from 1993 to 1995. Statistics of rain and total attenuation and frequency scaling of total attenuation are presented and commented in the light of the ITU-R predictions.

The ability of a synthetic aperture radar (SAR) to detect targets under foliage is in part determined by the attenuation suffered by radiation propagating through the foliage and the backscatter from the foliage. MIT Lincoln Laboratory made measurements of foliage attenuation and backscatter using the NASA/JPL UHF, L-, C-band fully-polarimetric SAR in July 1990. In this experiment, a 48 [km.sup.2] forested area near Portage, Maine was imaged. Twenty-seven 8 ft trihedral corner reflectors were arrayed throughout the imaged area in order to measure foliage attenuation. Ground truth was recorded at the time of the experiment in order to correlate the attenuation and backscatter results with foliage biophysical properties. The probability densities for foliage attenuation and for backscatter are determined as functions of frequency, polarization, and depression angle.