Christophe Craeye

A Body Area Propagation Model Derived From Fundamental Principles: Analytical Analysis and Comparison With Measurements

Using wireless sensors worn on the body to monitor health information is a promising new application. To realize transceivers targeted for these applications, it is essential to understand the body area propagation channel. Several numerical, simulated, and measured body area propagation studies have recently been conducted. While many of these studies are useful for evaluating communication systems, they are not compared against or justified by more fundamental physical models derived from basic principles. This type of comparison is necessary to provide better physical insights into expected propagation trends and to justify modeling choices. To address this problem, we have developed a simple and generic body area propagation model derived directly from Maxwells equations revealing basic propagation trends away, inside, around, and along the body. We have verified the resulting analytical model by comparing it with measurements in an anechoic chamber. This paper develops an analytical model of the body, describes the expected body area pathloss trends predicted by Maxwells equations, and compares it with measurements of the electric field close to the body.

Rain generated ring-waves: Measurements and modelling for remote sensing

We present an analysis of ring-wave and scatterometer data from a water surface that was agitated by simulated rain. Water droplets of 2.8 mm diameter impacted the water surface at almost terminal velocity, and the rain rates cover a wide range of conditions (5 to 200 mm hr(-1)). Both the ring-wave energy and backscattered power from the GHz scatterometer increase as R increases, but the growth rates slacken at higher rain intensities. Ring-wave frequency spectra and wavenumber spectra are well represented by log-Gaussian spectral models. The results can be used to guide development of microwave scattering models.

Impact of Antenna Coupling on 2

The impact of mutual coupling induced by two closely spaced minimum scattering antennas at the subscriber unit on 2 times 2 multiple-input multiple-output channels and communications is investigated. Both (de)correlation effects and variations of antenna gain resulting from coupling mechanisms are considered. Relationships between coupling and correlations/channel Frobenius norm are discussed, pointing out the role of the interelement spacing, the array orientation, and the richness of scattering. The analysis also yields useful insight into the influence of mutual coupling on capacity and system performance

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A fast numerical method, well-suited to the analysis of moderate-size arrays made of complex elements, is presented. It combines macro basis functions and multipole approaches, without an iterative procedure. This method is exploited to estimate the impedance matrix and active element patterns. For the latter, an efficient formulation is provided, as a series of pattern multiplication problems. Examples are shown for arrays of broadband dipoles. The computational gain obtained for the reduction of the original method of moments system of equations is briefly described

2 MIMO Communications

In strongly coupled antenna arrays, the behavior of the elements near the edge can exhibit very large deviations with respect to the infinite periodic array solution. Insight into these truncation effects can be obtained by simulating finite-by-infinite arrays. This paper describes an efficient method-of-moments (MoM) scheme for simulating such arrays. This scheme is capable of handling arrays of two-dimensional metallic antennas placed perpendicularly to the array plane, in lossless media. This formulation relies on the free-space Greens function related to arrays infinite in one direction only, with linear phase excitation. After extraction of its singular part, this function is tabulated. Then, the elements of the MoM impedance matrix are computed in the space domain, with the help of a limited number of integration points. The computation time needed for establishing the MoM system of equations and for solving it is comparable to the time needed in the linear array case. An extension of this formulation is also developed to study infinite-by-infinite arrays and semi-infinite arrays. The latter solutions also provide standard current distributions, which are used to obtain a fast approximate solution of the MoM system of equations. Simulation results are shown for broadband arrays, made of tapered slot antennas consisting of metallic plates.

A Fast Impedance and Pattern Computation Scheme for Finite Antenna Arrays

An approach based on the method of moments is presented for the computation of the sensitivity of infinite and finite receiving phased arrays with active beamforming networks. The sensitivity is characterized in terms of signal-to-noise element patterns. Coupling of noise through the array is included in the analysis, as well as noise resulting from losses in the antennas. Simulation results are shown for arrays consisting of tapered-slot antennas made of metallic plates. For finite arrays, the average signal-to-noise ratio per element is not necessarily smaller than in the infinite-arraycase. For an 8/spl times/8 array, the average signal-to-noise element pattern is somewhat more narrow than for the infinite array. At broadside, the sensitivity of relatively small arrays (4/spl times/4 to 8/spl times/8) is described within order 1 dB by the infinite-array solution.

An efficient MoM formulation for finite-by-infinite arrays of two-dimensional antennas arranged in a three-dimensional structure

We show that the public experiment held in Venice by Tamburini et al and reported in 2012 New J. Phys. 14 033001 can be regarded as a particular implementation of multiple-input–multiple-output (MIMO) communications and, therefore, has no advantages over established techniques. Moreover, we explain that the use of a ‘vortex’ mode (orbital angular momentum ` = 1) at one of the transmit antennas is not necessary to encode different channels since only different patterns—or similarly different pointing angles—of the transmit antennas are required. Finally, we identify why this MIMO transmission allowed the decoding of two signals, despite being line-of-sight. This is due to the large separation between the receiving antennas, which places the transmit antennas in the near-field Fresnel region of the receiving ‘array’. This severely limits the application of this technique in practice, since, for a fixed separation between receiving antennas, the detectable signal power from any additional vortex mode decays at least as 1/r 4.

MoM simulation of signal-to-noise patterns in infinite and finite receiving antenna arrays

Microwave signatures of the ocean surface are affected by wind and rain. To support the development of theoretical models for remote sensing applications, radar scatterometry experiments at 13.5 and 36 GHz with VV polarization were conducted at the Rain-Sea Interaction Facility at NASA Wallops. Backscatterings from rain drop impacts on fresh and salt water surfaces were measured with an incidence angle of 30 degrees for eight different drop sizes. Results are also presented for terminal and non-terminal fall velocities. Surface features were imaged by an ultrahigh-speed digital camera synchronized with radar data acquisition and their geometrical characteristics were determined. Backscattered powers from crowns, craters, stalks and ring-waves were measured and compared. These measurements confirm that for slant radar configurations, ring-waves are the dominant scattering contribution, even though stalk scattering is not negligible.

Comment on ‘Encoding many channels on the same frequency through radio vorticity: first experimental test’

An overview about mutual coupling analysis in antenna arrays is given. The relationships between array impedance matrix and embedded element patterns, including beam coupling factors, are reviewed while considering general-type antennas; approximations resulting from single-mode assumptions are pointed out. For regular arrays, a common Fourier-based formalism is employed, with the array scanning method as a key tool, to explain various phenomena and analysis methods. Relationships between finite and infinite arrays are described at the physical level, as well as from the point of view of numerical analysis, considering mainly the method of moments. Noise coupling is also briefly reviewed.

Scatterometric signatures of multivariate drop impacts on fresh and salt water surfaces

An efficient method-of-moments (MoM) technique for analyzing non-periodic antenna arrays of identical elements with fixed orientation is presented. The proposed method, which uses macro basis functions (MBFs), is based on a compact representation of the interactions between MBFs. These interactions are expressed via a low-order harmonic-polynomial function after an explicit pre-computation of the reaction integrals in a very limited set of relative positions. This is possible for arrays of arbitrary size thanks to three transformations- subtraction of the far-field expression for the interactions, phase correction and modified radial distance- applied successively to the pre-computed interactions. After obtaining the harmonic-polynomial expressions, the computation time for the reaction integral between two MBFs is independent from the complexity of the antenna array element.