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  • 1.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A survey of the application of the spherical vector wave mode expansion approach to antenna-channel interaction modeling2014In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, no 8, p. 663-679Article in journal (Refereed)
    Abstract [en]

    This paper provides an overview of recent advances in the modeling, analysis, and measurements of interactions between antennas and the propagation channel in multiple antenna systems based on the spherical vector wave mode expansion of the electromagnetic field and the antenna scattering matrix. It demonstrates the importance and usefulness of this approach to gain further insights into a variety of topics such as physics-based propagation channel modeling, mean effective gain, channel correlation, propagation channel measurements, antenna measurements and testing, the number of degrees of freedom of the radio propagation channel, channel throughput, and diversity systems. The paper puts particular emphasis on the unified approach to antenna-channel analysis at the same time as the antenna and the channel influence are separated. Finally, the paper provides the first bibliography on the application of the spherical vector wave mode expansion of the electromagnetic field to antenna-channel interactions.

  • 2. Beghin, Christian
    et al.
    Dècrèau, Pierrette
    Pickett, Jolene
    Sundkvist, David
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Lefebvre, Bertrand
    Modeling of CLUSTER's electric antennas in space: application to plasma diagnostics2005In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 40, no 6, p. RS6008-Article in journal (Refereed)
    Abstract [en]

    [1] The main characteristics of the long-boom electric antennas installed on board the Cluster satellites are derived from finite element modeling in a kinetic and isotropic space plasma, in the frequency range of about 1–100 kHz. The model is based on the surface charge distribution method in quasi-static conditions. The impedances of both types of antenna, i.e., the double-wire and the double-probe, are computed versus the frequency normalized with respect to the local plasma frequency and for several different Debye lengths. Most of the code outputs are checked using analytic estimations for better understanding of the involved physical mechanisms. As a by-product, the effective length of the double-probe antenna and the mutual impedance between the two antennas are computed by the code. It is shown that if it had been possible to implement such measurements on board, one would have been able not only to determine accurately the electric characteristics of the antennas but also to estimate the local plasma parameters. Nevertheless, an interesting feature predicted by the model has been checked recently in orbit by running a special mode of operation for testing the mutual impedance measurement. The preliminary results are globally consistent with the predictions, except that they suggest that our Maxwellian model for the electron distribution should be revised in order to explain the unexpected low-frequency response. After analysis of the electron flux measurements obtained simultaneously, it appears that a rough adjustment of the electron distribution with a two-component distribution allows us to account for the observations.

  • 3. Buehler, Stefan
    et al.
    Verdes, C.L.
    Universität Bremen, Institute of Environmental Physics.
    Tsujimaru, S.
    National Institute of Information and Communication Technology, Tokyo.
    Kleinbohl, A.
    Universität Bremen, Institute of Environmental Physics.
    Bremer, H.
    Universität Bremen, Institute of Environmental Physics.
    Sinnhuber, M.
    Universität Bremen, Institute of Environmental Physics.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Expected performance of the superconducting submillimeter-wave limb emission sounder compared with aircraft data2005In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 40, no 3, p. RS3016/1-RS3016/13Article in journal (Refereed)
    Abstract [en]

    The simulated retrieval performance of a submillimeter wave limb sounder was compared with that of an up-looking instrument with identical observation frequency bands and comparable noise temperature. The frequency bands were 624.32-626.32 and 649.12-650.32 GHz, and the retrieval simulations focused on the key trace gas species O-3, HCl, and ClO. As expected, the limb geometry leads to a better altitude resolution and larger measurement altitude range. The same retrieval setup was applied to measured spectra, taken by the up-looking Airborne Submillimeter Radiometer ( ASUR) instrument on 4 September 2002 at 19.11 degrees E, 71.90 degrees N and on 19 September 2002 at 44.10 degrees E, 4.10 degrees S. The observed structures in the fit residual near the HCl spectral lines at 625.9 GHz lead to the conclusion that the pressure shift parameter of HCl is likely to be higher than the value in the HITRAN spectroscopic database. Depending on the assumed temperature dependence of the shift, the HCl pressure shift value consistent with the ASUR data is 0.090-0.117 MHz/hPa instead of the 0.030 MHz/hPa reported in HITRAN. This result is in good agreement with very recent independent laboratory work which suggests a value of 0.110 MHz/hPa for the shift.

  • 4.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A study of edge effects in triangular grid tapered-slot arrays using coupling coefficients2010In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, p. RS2005-Article in journal (Refereed)
    Abstract [en]

    Edge effects for tapered-slot elements in triangular grid array antennas are studied by using finite difference time domain codes. The S parameters for finite-by-infinite arrays are computed and evaluated for two different edge models and, to evaluate the edge effects, the results are compared with the S parameters for the infinite array. As expected, the largest difference between the results occurs for the elements closest to the edges, because of the missing coupling from nearby elements and the perturbed element currents due to the edge geometry. By using the proposed method it is possible to distinguish between these two edge effects. A method to combine the finite-by-infinite array results and the infinite array results is presented and used to characterize the perturbation caused by the truncation of the infinite array.

  • 5.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Murtagh, Donal
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Elgered, Gunnar
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Kuhn, Thomas
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Measurement of tropospheric/stratospheric transmission at 10–35 GHz for H2O retrieval in low Earth orbiting satellite links2003In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 38, no 4, p. 8069-Article in journal (Refereed)
    Abstract [en]

    Active microwave limb sounding is a possible technique for measuring water vapor in the upper troposphere and lower stratosphere, and here a first assessment of the retrieval capabilities of transmission measurements in the range 10–35 GHz is presented. The proposed observing system consists of a constellation of low Earth orbiters measuring atmospheric transmission at the frequencies 10.3, 17.2, and 22.6 GHz. The use of these relatively long wavelengths guarantees a minimal, for being a remote sensing technique, influence from scattering. The original objective of the measurements was to derive water vapor profiles, but the potential to retrieve the liquid water content of clouds was also identified during the study. Retrieval errors due to thermal noise, gain instability, and spectroscopic uncertainties were considered. With the assumed instrument characteristics a measurement precision for water vapor in the upper troposphere of 5–10% is obtained, with capability to observe through ice clouds and clouds with a low water content.

  • 6. Fornieles-Callejon, J.
    et al.
    Salinas, A.
    Toledo-Redondo, Sergio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Porti, J.
    Mendez, A.
    Navarro, E. A.
    Morente-Molinera, J. A.
    Soto-Aranaz, C.
    Ortega-Cayuela, J. S.
    Extremely low frequency band station for natural electromagnetic noise measurement2015In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 50, no 3, p. 191-201Article in journal (Refereed)
    Abstract [en]

    A new permanent ELF measurement station has been deployed in Sierra Nevada, Spain. It is composed of two magnetometers, oriented NS and EW, respectively. At 10 Hz, their sensitivity is 19 V/pT and the signal-to-noise ratio (SNR) is 28 dB for a time-varying signal of 1 pT, the expected field amplitude in Sierra Nevada. The station operates for frequencies below 24 Hz. The magnetometers, together with their corresponding electronics, have been specifically designed to achieve such an SNR for small signals. They are based on high-resolution search coils with ferromagnetic core and 10(6) turns, operating in limited geometry configuration. Different system noise sources are considered, and a study of the SNR is also included. Finally, some initial Schumann resonance measurements are presented in order to validate the performance of the measurement station, including 1 h length spectra, daily variations of resonance amplitudes and frequencies for the different seasons, and a 3 day spectrogram.

  • 7. Gustafsson, M.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    An optimization approach to two-dimensional time domain electromagnetic inverse problems2000In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 35, no 2, p. 525-536Article in journal (Refereed)
  • 8.
    He, Sailing
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Popov, M.
    Romanov, V.
    Explicit full identification of a transient dipole source in the atmosphere from measurement of the electromagnetic fields at several points at ground level2000In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 35, no 1, p. 107-117Article in journal (Refereed)
  • 9.
    Isoz, Oscar
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kinch, Kjartan
    Niels Bohr Institute, Copenhagen University.
    Bonnedal, Magnus
    RUAG Space, Gothenburg.
    Akos, Dennis
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver2014In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, no 1, p. 1-6Article in journal (Refereed)
    Abstract [en]

    [1] It is well known that terrestrial GPS/Global Navigation Satellite Systems (GNSS) receivers are vulnerable and have suffered from intentional and unintentional interference sources. Unfortunately, space-based GPS/GNSS receivers are not exempt from radio frequency interference originating from the Earth. This paper explores data recorded by the GNSS Receiver for Atmospheric Sounding (GRAS) instrument onboard MetOp-A in September 2007, which is assumed to be representative of the typical environment for GPS/GNSS instrumentation in LEO orbit. Within these data it is possible to detect both pulsed interference and variations in the background noise. One plausible source of the pulsed interference is identified. We also show that neither the pulsed interference nor the variations in the background noise degrades the performance of the higher level products from GRAS

  • 10. Johansson, Gustav
    et al.
    Borg, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Nordenvaad, Magnus Lundberg
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Wannberg, Gudmund
    Swedish Institute of Space Physics.
    Simulation of post-ADC digital beamforming for large aperture array radars2010In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, no RS3001Article in journal (Refereed)
    Abstract [en]

    This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.

  • 11.
    Leyser, Thomas B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waldemarsson, F.
    Buchert, Stephan C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Plasma angular momentum effects and twisted incoherent scatter radar beams2012In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 47, p. RS5004-Article in journal (Refereed)
    Abstract [en]

    Phased arrays provide new possibilities for remote sensing with radars. By imposing an azimuthal phase variation, electromagnetic beams that carry orbital angular momentum can be formed. Such beams have a phase structure that appears twisted and as a result an intensity null in the center of the beam cross section. Here we numerically investigate twisted beams for incoherent scatter radars that are used to study the ionosphere. We discuss the possibility of utilizing such radar beams to probe twisted beams of plasma waves and flows transverse to the beam axis, such as associated with auroral arcs. Transverse plasma flows may give rise to a rotational frequency shift of the scatter from a twisted beam and Doppler broadening due to the beam divergence, the latter also occurring with regular beams. Although the angular momentum effects of the considered large scale flows are generally small, sheared and vortical flows transverse to the beam axis can in principle be discriminated from unidirectional flows with beams carrying orbital angular momentum.

  • 12.
    Melsheimer, C.
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Verdes, C.
    Buehler, Stefan
    Intercomparison of general purpose clear sky atmospheric radiative transfer models for the millimeter/submillimeter spectral range2005In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 40, no 1, p. RS1007-Article in journal (Refereed)
    Abstract [en]

    We compare a number of radiative transfer models for atmospheric sounding in the millimeter and submillimeter wavelength range, check their consistency, and investigate their deviations from each other. This intercomparison deals with three different aspects of radiative transfer models: (1) the inherent physics of gaseous absorption lines and how they are modeled, (2) the calculation of absorption coefficients, and (3) the full calculation of radiative transfer for different geometries, i.e., up-looking, down-looking, and limb-looking. The correctness and consistency of the implementations are tested by comparing calculations with predefined input such as spectroscopic data, line shape, continuum absorption model, and frequency grid. The absorption coefficients and brightness temperatures calculated by the different models are generally within about 1% of each other. Furthermore, the variability or uncertainty of the model results is estimated if (except for the atmospheric scenario) the input such as spectroscopic data, line shape, and continuum absorption model could be chosen freely. Here the models deviate from each other by about 10% around the center of major absorption lines. The main cause of such discrepancies is the variability of reported spectroscopic data for line absorption and of the continuum absorption model. Further possible causes of discrepancies are different frequency and pressure grids and differences in the corresponding interpolation routines, as well as differences in the line shape functions used, namely a prefactor of (nu/nu(0)) or (nu/nu(0))(2) of the Van-Vleck-Weisskopf line shape function. Whether or not the discrepancies affect retrieval results remains to be investigated for each application individually.

  • 13.
    Mohammadi, Siavoush M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Daldorff, Lars K. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Forozesh, Kamyar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Thide, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Bergman, Jan E. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Isham, Brett
    Karlsson, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Carozzi, T. D.
    Orbital angular momentum in radio: Measurement methods2010In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, p. RS4007-Article in journal (Refereed)
    Abstract [en]

    Novel measurement and approximation methodologies for studying orbital angular momentum (OAM) modes in radio beams, i.e., electromagnetic beam modes having helical phase fronts, are presented. We show that OAM modes can be unambiguously determined by measuring two electric field components at one point, or one electric field component at two points.

  • 14.
    Olsson, Olle
    Luleå tekniska universitet.
    Scattering of electromagnetic wave by a perfectly conducting half plane below a stratified overburden1978In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 13, no 2, p. 391-397Article in journal (Refereed)
    Abstract [en]

    By expanding the electromagnetic field into plane wave eigenfunctions, an integral equation is obtained which describes the coupling between an overburden, consisting of an arbitrary number of plane layers and an arbitrary object beneath a stratified half space. As an example of the technique, a perfectly conducting half plane inclined to the strata in a substratum is discussed. In this case the kernel of the integral equation may be expressed in terms of elementary functions. Numerical results are discussed for a plane wave incident on the ground

  • 15.
    Olsson, Olle
    Luleå tekniska universitet.
    Scattering of electromagnetic waves by a perfectly conducting half plane below a stratified overburden1978In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 13, p. 391-397Article in journal (Refereed)
    Abstract [en]

    By expanding the electromagnetic field into plane wave eigenfunctions, an integral equation is obtained which describes the coupling between an overburden, consisting of an arbitrary number of plane layers and an arbitrary object beneath a stratified half space. As an example of the technique, a perfectly conducting half plane inclined to the strata in a substratum is discussed. In this case the kernel of the integral equation may be expressed in terms of elementary functions. Numerical results are discussed for a plane wave incident on the ground.

  • 16.
    Persson, Patrik
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Rojas, Roberto G.
    High-frequency approximation for mutual coupling calculations between apertures on a perfect electric conductor circular cylinder covered with a dielectric layer: Nonparaxial region2003In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 38, no 4, p. 1079-Article in journal (Refereed)
    Abstract [en]

    An asymptotic Green's function technique is presented for the calculation of the surface fields on a perfect electric conductor circular cylinder covered with a dielectric layer. The sources are apertures located on the perfect electric conductor surface. This method is very efficient and valid for large cylinders in terms of wavelengths. The new representation is obtained via Watson's transformation and integral contour deformations. The efficiency of the method results from the circumferentially propagating representation of the Green's function as well as the efficient numerical evaluation of various integrals. Numerical results are presented showing good agreement when compared to other solutions as well as measurements.

  • 17.
    Podlipenko, Yu K.
    et al.
    Faculty of Cybernetics, Taras Shevchenko National University of Kyiv, Kiev, Ukraine.
    Shestopalov, Yury V.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Mathematics.
    Guaranteed estimation of solutions to Helmholtz transmission problems with uncertain data from their indirect noisy observations2017In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 52, no 9, p. 1129-1139Article in journal (Refereed)
    Abstract [en]

    We investigate the guaranteed estimation problem of linear functionals from solutions to transmission problems for the Helmholtz equation with inexact data. The right-hand sides of equations entering the statements of transmission problems and the statistical characteristics of observation errors are supposed to be unknown and belonging to certain sets. It is shown that the optimal linear mean square estimates of the above mentioned functionals and estimation errors are expressed via solutions to the systems of transmission problems of the special type. The results and techniques can be applied in the analysis and estimation of solution to forward and inverse electromagnetic and acoustic problems with uncertain data that arise in mathematical models of the wave diffraction on transparent bodies.

  • 18.
    Sandström, Sven-Erik
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Akeab, Imad
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    A study of some FMCW radar algorithms for target location at low frequencies2016In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 51, no 10, p. 1676-1685Article in journal (Refereed)
    Abstract [en]

    FMCW (Frequency Modulated Continuous Wave) radar is a simple and inexpensive technique for target location. The resolution is given by the available bandwidth and the directivity of the antenna. Resolution is not a problem at high frequencies, while at low frequencies, and especially for mobile platforms, the required size of the antenna becomes impractical. In order to obtain the bearing of the targets, without relying on directivity, one may use a simple two-dimensional trilateration method that involves several platforms. The problem of ghost targets has been studied for both monostatic and multistatic radar. When there is a confluence of echoes, the relation between accuracy and bandwidth is of particular interest. 

  • 19.
    Sandström, Sven-Erik
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Akeab, Imad
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Scaling and sparsity in an accurate implementation of the method of moments in 2-D2014In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, no 8, p. 643-652Article in journal (Refereed)
    Abstract [en]

    The integral equations of electromagnetic scattering are often solved numericallyby means of the method of moments. At high frequencies, this method typically leads to a large linear system with a dense matrix. Higher order basis functions is a means to improve the accuracy. B-splines are used here for a two-dimensional testbed study that avoids the complexity of 3D implementation.

    For smooth convex scatterers one may use \emph{a priori} knowledge about the oscillatory behaviour of the solution to reformulate the integral equation.This fast scale of variation is included in the kernel of the integral equation. An extension of this idea deals with the variation in the shadow, particularly for circular geometry, and is an improvement that is presented in this study. Generally, the TE-case is less studied at high frequencies and our numerical results therefore relate to this harder problem.

    A sparse matrix can be obtained by modification of the integration path in the integral equation. The decay of the modified kernel makes this possible for high frequencies but the modified path reduces the accuracy in the deep shadow. This study investigates these modified paths for the case where the shadow region is not omitted from the formulation.

  • 20.
    Shoory, Abdolhamid
    et al.
    Electromagnetic Compatibility Laboratory, Swiss Federal Institute of Technology, Lausanne, Schweiz.
    Mimouni, Abdenabi
    Laboratoire de Génie Physique, Ibn Khaldoun University, Tiaret, Algeriet.
    Rachidi, Farhad
    Electromagnetic Compatibility Laboratory, Swiss Federal Institute of Technology, Lausanne, Schweiz.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rubinstein, Marcos
    Dept of Electrical Engineering and Computer Science, University of Applied Sciences of Western Switzerland, Yverdon-les-Bains, Schweiz.
    On the accuracy of approximate techniques for the evaluation of lightning electromagnetic fields along a mixed propagation path2011In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 46, p. RS2001-Article in journal (Refereed)
    Abstract [en]

    In this paper we review simplified analytical expressions derived by Wait using the concept of attenuation function for the analysis of the propagation of lightning-radiated electromagnetic fields over a mixed propagation path (vertically stratified ground). Two different formulations proposed by Wait that depend on the relative values of ground surface impedances are discussed. It is shown that both formulations give nearly the same results for the time domain electric field. However, depending on the values of the normalized surface impedance for each ground section, the use of one of the two formulations is computationally more efficient. The accuracy of the Wait formulations was examined taking as reference full-wave simulations obtained using the finite difference time domain technique. It is shown that Wait's simplified formulas are able to reproduce the distant field peak and waveshape with a good accuracy.

  • 21.
    Tamburini, F.
    et al.
    Twistoff SRL, Padua, Italy.;Univ Padua, Dept Phys & Astron, Padua, Italy..
    Mari, E.
    Twistoff SRL, Padua, Italy.;Univ Padua, Dept Phys & Astron, Padua, Italy..
    Parisi, G.
    Twistoff SRL, Padua, Italy..
    Spinello, F.
    Twistoff SRL, Padua, Italy.;Univ Padua, Dept Informat Engn, Padua, Italy..
    Oldoni, M.
    SIAE Microelettron, Cologno Monzese, Italy..
    Ravanelli, R. A.
    SIAE Microelettron, Cologno Monzese, Italy..
    Coassini, P.
    SIAE Microelettron, Cologno Monzese, Italy..
    Someda, C. G.
    Twistoff SRL, Padua, Italy..
    Thidé, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Romanato, F.
    Twistoff SRL, Padua, Italy.;Univ Padua, Dept Phys & Astron, Padua, Italy..
    Tripling the capacity of a point-to-point radio link by using electromagnetic vortices2015In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 50, no 6, p. 501-508Article in journal (Refereed)
    Abstract [en]

    In this paper we report the results from outdoor experiments showing that it is possible to increase the data transmission capacity using at least three coherent, orthogonal beams on the same frequency, 17.128GHz, each in a unique orbital angular momentum state. Each beam was encoded with the digital modulations used in present-day telecommunications. We achieved an error-free throughput of 3x11Mbit/s with four-Quadrature Amplitude Modulation over a 7MHz bandwidth over 100m and 150m long links.

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