The Ultrawideband Leaky Lens Antenna

A novel directive and nondispersive antenna is presented: the ultrawideband (UWB) leaky lens. It is based on the broad band Cherenkov radiation occurring at a slot printed between different infinite homogeneous dielectrics. The first part of the paper presents the antenna concept and the UWB design. The issues that are specifically addressed include the impedance matching, the radiation pattern and the phase purity. Subsequently the hardware demonstrator and the results of the measurement campaign are shown. The results fully validate the antenna concept. The antenna presents decade bandwidth impedance matching, directive and frequency independent patterns in the H-plane over two octaves, negligible cross-polarization levels, weak amplitude dispersivity and, according to the authors, the most stable phase center for a directive antenna over an ultra wide frequency range.     

Closed-form transmission line model for radiated susceptibility in metallic enclosures

This work presents an approximate frequency domain mathematical model based on the transmission line (TL) theory for field-to-wire coupling in a rectangular metallic enclosure. The currents and voltages at the terminations of a TL induced by known electromagnetic (EM) field sources are expressed in closed form. Validity limits and applicability of the model are discussed by comparing the analytical TL-based predictions with the outputs of a full-wave numerical analysis of the overall structure using a three-dimensional finite integration technique. Deviations from the full-wave solution, due to the scattered field from the TL, have been identified, analyzed, and discussed. The proposed analytical model proves to be generally suited for accurate prediction of radiated susceptibility of single-ended interconnections in closed environments.     

Simulating coherent backscattering from crops during the growingcycle

The backscattering coefficient and the position of interferometric phase center of wheat and sunflowers during the growing cycle have been computed by using a coherent electromagnetic model. In the model, the scattered fields are added coherently and the attenuation in the canopy is computed by means of Foldy's approximation. The comparison between model simulations and experimental data has shown that model results match reasonably well with the measured backscattering. As the plant grows, the backscattering of wheat ("narrow leaf" crop) decreases, whereas that of sunflowers ("broad leaf") increases. An analysis of the various terms that contribute to backscattering has indicated that the most significant contribution is given by the double scattering soil-stalk and that the position of the interferometric phase center is close to the soil. When the contribution of leaves is more significant, as in the case of sunflowers, the interferometric phase center goes up to about one quarter of the full plant height. This result demonstrates the potential of the interferometric observation in providing significant new information on crop classification algorithms based on scattering mechanisms     

The relationship between the backscattering coefficient and thebiomass of narrow and broad leaf crops

The influence of the shape and dimensions of plant constituents on the backscattering of agricultural vegetation is investigated. Multifrequency multitemporal polarimetric data, collected at C- and L-bands by means of airborne and satellite synthetic aperture radar (SAR), showed that the relations between the backscattering of crops and the vegetation biomass depend on plant type, and that there are different trends for “narrow” and “broad” leaf crops. In the latter crops, backscattering increases with an increase in the biomass, especially at L-band. This behavior is typical of media in which scattering is dominant, whereas on “narrow leaf” plants, the trend is flat or decreasing, denoting a major contribution of absorption. Theoretical simulations obtained with a discrete element radiative transfer model have confirmed that a different backscattering of crops with the same biomass may be due to plant geometry