Miguel Ferrando

Fast convolution with free-space Green's functions

We introduce a fast algorithm for computing volume potentials - that is, the convolution of a translation invariant, free-space Greens function with a compactly supported source distribution defined on a uniform grid. The algorithm relies on regularizing the Fourier transform of the Greens function by cutting off the interaction in physical space beyond the domain of interest. This permits the straightforward application of trapezoidal quadrature and the standard FFT, with superalgebraic convergence for smooth data. Moreover, the method can be interpreted as employing a Nystrom discretization of the corresponding integral operator, with matrix entries which can be obtained explicitly and rapidly. This is of use in the design of preconditioners or fast direct solvers for a variety of volume integral equations. The method proposed permits the computation of any derivative of the potential, at the cost of an additional FFT.

Novel UWB antennas with switchable and tunable band-notched behaviors

The objective of this paper is to further improve the antenna filtering capability by making this band- notched behavior switchable. Depending on whether interference from other systems is present or not, the antenna filtering feature can be activated. This work was initiated in F. Antonio-Daiu et al. (2006), but evolved designs with more promising results will be presented here. An antenna with similar performance was presented in V. A. Shameena et al. (2006), but some important differences exist, which will be discussed later. Moreover, using a similar configuration to that of the switchable antenna, a further improvement can be introduced to the band-notched UWB antenna by making the rejected frequency tunable.

Active balanced feeding for compact wideband antennas

This paper demonstrates the advantages of using active devices, which have balanced complex impedance, for feeding wideband antennas. Some techniques to simultaneously increase the frequency bandwidth and reduce antenna dimensions are also discussed.

A new Fast Physical Optics method for very large PEC surfaces

A new 3D Fast Physical Optics method is presented for computing backscattered fields at high frequencies of PEC parabolic surfaces. This method can be easily extended to more complex surfaces. By virtue of Cauchy theorem a suitable surface deformation is used to convert a double highly oscillatory integral into a double slow varying integral, easily calculable by means of Gaussian quadrature.

Modal analysis of a MIMO antenna for sensor networks

Multiple antennas have emerged as an important technology for increasing the efficiency of wireless communication systems. multiple-input multiple-output (MIMO) systems, offering significant capacity gain, can be used to maximise the transmission channel throughput or to decrease the channel fading. However, multiple antennas are not easily integrated in mobile devices or sensors, because the space available is usually limited. Moreover, in order to lead high performances, good isolation and decoupling between antennas are required. Another drawback is that multiple antennas require multiple RF devices for signal processing that are very expensive. To suppress mutual coupling several methods were proposed in the available literature. In [1] the distance between MIMO antennas array was increased mounting them at the corner of a PDA. In [2] several parasitic elements were employed between MIMO antenna array, while in [3] band-notch slots on a ground plane were etched. In this paper we propose a new MIMO antenna that consists in a metallic ring fed at four ports with alternate phase. The alternate phase of the feeding leads to the excitation of orthogonal modes and allows the implementation of the MIMO antenna. The antenna has been analysed using the Theory of Characteristic Modes [4], which is really appropriate to design multimode antennas because of the physical insight it provides.

Asymptotic phase extraction as a preconditioning technique for mom

The most common preconditioners are of algebraic nature, based on sparse inverse approximations of the MoM matrix Z, like the incomplete LU decomposition (ILU). An improvement in the condition number can be also obtained directly in Z using appropriate basis functions, such as higher order basis functions, and multi-resolution techniques. The asymptotic phase integral equation method (AP-IE) is also a method to increase the range of applicability of MoM for high frequencies and smooth scatterers.

Rigorous analysis by means of PO-MoM of large PEC scattering problems

A method is introduced for reducing the dependence on matrix formation time, solution time and computer storage in the method of moments (MoM) for high frequency electromagnetic scattering problems. This method combines asymptotic phasefront extraction (APE) with an efficient calculation of the impedance integrals.

Decoupled field integral equations for electromagnetic scattering from homogeneous penetrable obstacles

ABSTRACT We present a new method for the analysis of electromagnetic scattering from homogeneous penetrable bodies. Our approach is based on a reformulation of the governing Maxwell equations in terms of two uncoupled vector Helmholtz systems: one for the electric field and one for the magnetic field. This permits the derivation of resonance-free Fredholm equations of the second kind that are stable at all frequencies, insensitive to the genus of the scatterers, and invertible for all passive materials including those with negative permittivities or permeabilities. We refer to these as decoupled field integral equations.

Fast physical optics using piecewise quadratic approximation

The physical optics (PO) approximation is a well-known technique used to analyze very large conducting structures. In scattering problems and radiation of large reflectors, the PO technique provides acceptable accuracy [1] for some applications. This technique allows avoiding the hard solution of the Method of Moment (MoM) linear system by approximating this solution by the explicit PO current.

Electric field integral equation and the physical optics approximation

The aim of this paper is the study of some asymptotic properties and invariances of the Electric Field Integral Equation (EFIE) when applied to large and smooth structures. It is theoretical in nature, and thus no numerical results are included in this communication.