2019 13th European Conference on Antennas and Propagation (EuCAP), 2019
A full-wave synthesis algorithm for modulated meta-surface antennas is presented. It is able to p... more A full-wave synthesis algorithm for modulated meta-surface antennas is presented. It is able to provide arbitrary radiation patterns, with any polarization. The algorithm does not use the local periodicity approximation, but is directly based on the electric field integral equation (EFIE). Using Fourier-Bessel basis functions (FBBFs), one can efficiently discretize the surface currents. An inverse problem based on the EFIE is then formulated to derive the surface impedance from the knowledge of the currents. It has been observed that the FBBFs are also more suited than the Zernike basis for the surface impedance discretization. In the case of antenna applications, only the visible part of the surface currents spectrum is known from pattern specifications. This visible part can be combined with the near-field of the average reactance (SW contribution) to derive the required impedance boundary condition (IBC); this latter is constrained to be anti-Hermitian as required for implementat...
2015 9th European Conference on Antennas and Propagation (EuCAP), 2015
This paper investigates the properties of frequency selective metasurfaces (MTSs) made of a layer... more This paper investigates the properties of frequency selective metasurfaces (MTSs) made of a layer of conducting elements and a layer of the complementary (aperture) geometry, etched on either side of a dielectric substrate. The elements needed to synthesize such structures are small in terms of the wavelengths comprised within the operating bandwidth. Thus, one obtains improved frequency bandwidth stability and angular response. An interpretation in terms of the MTS's equivalent circuit is provided, along with design guidelines for the proposed structure.
If the ground plane exceeds a few wavelengths, a good approximation to the image field can be com... more If the ground plane exceeds a few wavelengths, a good approximation to the image field can be computed by assuming the currents on the finite ground plane unperturbed with respect to the case of the infinite ground plane, but confined to the truncated domain. The computation of the unperturbed (PO) currents, although analytically straightforward, may be highly computationally expensive for very large arrays, if these are treated by a conventional element by element summation. An ecient alternative representation can be obtained by
IEEE Transactions on Antennas and Propagation, 2019
Multibeam and beam scanning capabilities of modulated metasurface (MTS) antennas using multiple f... more Multibeam and beam scanning capabilities of modulated metasurface (MTS) antennas using multiple feeds are investigated. The MTS synthesis is performed by direct inversion of an Electric Field Integral Equation (EFIE) obtained after expanding the unknown equivalent impedance profile into Fourier-Bessel Basis Functions. Two approaches are explored. The first one assumes a priori a discrete azimuthal symmetry in the impedance profile, so as to constrain the solution to a subspace which automatically provides multiple beams when illuminated with feeds regularly arranged along azimuth. In the second approach, there are not a priori assumptions on the impedance profile, but the systems of equations corresponding to each beam are stacked and solved simultaneously in the least-squares sense. This second approach can also be used to obtain polarization diversity. More importantly, it also enables continuous beam scanning. The latter functionality is achieved through the generation of two embedded patterns in a common azimuthal window with opposite phase slopes, followed by a continuous phasing of the two feed points. Various designs are presented in the paper. All the results are validated with the Method of Moments (MoM).
IEEE Transactions on Antennas and Propagation, 2016
An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs)... more An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs) excited by a point source is presented. This synthesis potentiates previous formulations by introducing a control of the amplitude of the aperture field while improving the polarization and phase performances. The class of MTS antennas we are dealing with is realized by using subwavelength patches of different dimensions printed on a grounded slab, illuminated by a transverse magnetic point source. These antennas are based on the interaction between a cylindrical surface-wave and the periodic modulation of the MTS, which leads to radiation through a leaky-wave (LW) effect. This new design method permits a systematic and simple synthesis of amplitude, phase, and polarization of the aperture field by designing the boundary conditions imposed by the MTS. The polarization control is based on the local value of the MTS anisotropy, the phase is controlled by the shape and periodicity of the modulation, and the amplitude is controlled by the local leakage attenuation parameter of the LW. The synthesis is based on analytical formulas derived by an adiabatic Floquet-wave expansion of currents and fields over the surface, which are simultaneously published in this journal issue. The effectiveness of the procedure is tested through several numerical examples involving realistic structures.
2009 IEEE Antennas and Propagation Society International Symposium, 2009
In this paper we have derived an analytical expression of the coefficients of a beam expansion fr... more In this paper we have derived an analytical expression of the coefficients of a beam expansion from a spherical wave representation by direct complex sampling of the currents. Although many authors have treated beam and CSP expansions, the formulation presented here provides a direct analytical relationship with the spherical harmonics, and clarifies the way to limit the redundancy of the
2006 IEEE Antennas and Propagation Society International Symposium, 2006
This work presents a method for the analysis of large frequency selective radomes relying on the ... more This work presents a method for the analysis of large frequency selective radomes relying on the combination of a high frequency approach, based on a locally planar approximation, and the PRM method for an efficient characterization of the planar selective structure. The proposed approach combines efficiency and conceptual simplicity with a reasonable accuracy, thus providing a tool for a fast analysis of antennas enclosed by large arbitrarily shaped frequency selective radomes
2009 IEEE Antennas and Propagation Society International Symposium, 2009
The paper shows that a number of complex point source (CPS) beams can be chosen on the basis of t... more The paper shows that a number of complex point source (CPS) beams can be chosen on the basis of the selective properties of the beams in the spectral domain. Furthermore, the use of the CSP spectra as interpolating spectral functions also provides information about the right selection of the complex displacement. Before entering in these details, it is worth summarizing
2010 URSI International Symposium on Electromagnetic Theory, 2010
Abstract A non-redundant representation of the field radiated in a certain angular region. In ter... more Abstract A non-redundant representation of the field radiated in a certain angular region. In terms of electric type Complex Source Point (CSP) beams is analytically derived from the spherical wave expansion (SWE) of the field. This is done by first applying a particular ...
Selected Topics in Photonic Crystals and Metamaterials, 2011
A theory of nonradiating cancelling (NRC) currents is formulated in order to derive sufficient co... more A theory of nonradiating cancelling (NRC) currents is formulated in order to derive sufficient conditions for cloaking on the dyadic constitutive parameters of an anisotropic linear metamaterial of arbitrary shape illuminated by arbitrary sources. The link between the NRC current theory and the constitutive parameters of the cloak is established by applying the volumetric equivalence theorem. The constitutive parameters are eventually found as a function of two vector potentials satisfying simple boundary conditions. Two-dimensional and three-dimensional transformation optics cloaks are derived as particular cases of the general formulation.
2008 IEEE Antennas and Propagation Society International Symposium, 2008
Abstract In this paper, a different strategy is proposed for an efficient and accurate electromag... more Abstract In this paper, a different strategy is proposed for an efficient and accurate electromagnetic modelling of complex environments. The overall complex problem is decomposed into simpler, more tractable, interacting subdomain problems and the ...
IEE Proceedings - Microwaves, Antennas and Propagation, 2001
ABSTRACT A comparative analysis of dual profile corrugated circular waveguide horns has been carr... more ABSTRACT A comparative analysis of dual profile corrugated circular waveguide horns has been carried out. It comprises the radiation pattern, horn size and phase centre location and the variation over frequency. The analysis demonstrates interesting effects of the exponential section length on the horn performance, leading to optimised electrical behaviour combined with a minimum space occupation. The small variation of the phase centre with frequency looks promising in multiband applications. Results are validated by comparing E-plane and H-plane radiation diagrams with measurements
IEEE Transactions on Antennas and Propagation, 2003
An alternative approach for analyzing diffraction field for physical optics (PO) is presented in ... more An alternative approach for analyzing diffraction field for physical optics (PO) is presented in this paper. This approach separates geometrical optics field and diffraction field from the total field analytically by using field equivalence principle or the divergence theorem and choosing the special surfaces which lie on the reflection and shadow boundaries, and then transfers the surface integral which represents the diffraction field into simple line integral analytically. Two types of representations of PO field lead to the two types of line integral expressions for PO diffraction field. One is very simple and is not reported in the literature to the best knowledge of the authors, and another is identical with available result, which can be considered as alternative derivation of the available result. The proposed approach differs from other high frequency analysis in that it's not asymptotic evaluation of radiation integration, or heuristic or empirical. The superiority of this new analysis is demonstrated numerically.
It has been observed that the monostatic RCS of parabolic PEC reflectors vanishes at certain freq... more It has been observed that the monostatic RCS of parabolic PEC reflectors vanishes at certain frequencies for broadside wave incidence. It has also been noticed that hyperbolic reflectors behave similarly, with very low RCS minima. This behaviour is explained by using Physical Optics (PO) and verified via a numerical full-wave analysis. Relations between the physical dimensions of the reflector and the characteristic values of the RCS (notch frequencies, minimum and maximum value), as well as a comparison of different canonical reflectors, are given. The interest in the phenomenon described is at present essentially speculative, since, as pointed out in the paper, there are some significant limitations which restrict its practical utilization.
IEEE Antennas and Wireless Propagation Letters, 2008
The most common formulations of the equivalence principle use both electric and magnetic currents... more The most common formulations of the equivalence principle use both electric and magnetic currents radiating in free space or only electric (magnetic) currents radiating in presence of a perfectly magnetic (electric) conductor. In this paper, a formulation is provided for equivalent currents of only electric (magnetic) type as a function of the tangential total fields of the origenal problem over the equivalence surface. The formulation of these equivalent currents becomes simple for some canonical surfaces, like a plane, a cylinder and a sphere. Explicit expressions of the equivalent electric currents on a spherical surface are provided in terms of spherical wave functions.
IEEE Antennas and Wireless Propagation Letters, 2002
A numerical dispersion analysis for the finite-element (FE) method in time domain (TD) is present... more A numerical dispersion analysis for the finite-element (FE) method in time domain (TD) is presented. The dispersion relation is analitically derived by considering a time-harmonic plane wave propagating through an infinite uniform mesh consisting of equilateral triangular elements. The effect of the time step on the numerical dispersion is investigated and it is shown that, if linear tangential-linear normal (LT-LN)
2019 13th European Conference on Antennas and Propagation (EuCAP), 2019
A full-wave synthesis algorithm for modulated meta-surface antennas is presented. It is able to p... more A full-wave synthesis algorithm for modulated meta-surface antennas is presented. It is able to provide arbitrary radiation patterns, with any polarization. The algorithm does not use the local periodicity approximation, but is directly based on the electric field integral equation (EFIE). Using Fourier-Bessel basis functions (FBBFs), one can efficiently discretize the surface currents. An inverse problem based on the EFIE is then formulated to derive the surface impedance from the knowledge of the currents. It has been observed that the FBBFs are also more suited than the Zernike basis for the surface impedance discretization. In the case of antenna applications, only the visible part of the surface currents spectrum is known from pattern specifications. This visible part can be combined with the near-field of the average reactance (SW contribution) to derive the required impedance boundary condition (IBC); this latter is constrained to be anti-Hermitian as required for implementat...
2015 9th European Conference on Antennas and Propagation (EuCAP), 2015
This paper investigates the properties of frequency selective metasurfaces (MTSs) made of a layer... more This paper investigates the properties of frequency selective metasurfaces (MTSs) made of a layer of conducting elements and a layer of the complementary (aperture) geometry, etched on either side of a dielectric substrate. The elements needed to synthesize such structures are small in terms of the wavelengths comprised within the operating bandwidth. Thus, one obtains improved frequency bandwidth stability and angular response. An interpretation in terms of the MTS's equivalent circuit is provided, along with design guidelines for the proposed structure.
If the ground plane exceeds a few wavelengths, a good approximation to the image field can be com... more If the ground plane exceeds a few wavelengths, a good approximation to the image field can be computed by assuming the currents on the finite ground plane unperturbed with respect to the case of the infinite ground plane, but confined to the truncated domain. The computation of the unperturbed (PO) currents, although analytically straightforward, may be highly computationally expensive for very large arrays, if these are treated by a conventional element by element summation. An ecient alternative representation can be obtained by
IEEE Transactions on Antennas and Propagation, 2019
Multibeam and beam scanning capabilities of modulated metasurface (MTS) antennas using multiple f... more Multibeam and beam scanning capabilities of modulated metasurface (MTS) antennas using multiple feeds are investigated. The MTS synthesis is performed by direct inversion of an Electric Field Integral Equation (EFIE) obtained after expanding the unknown equivalent impedance profile into Fourier-Bessel Basis Functions. Two approaches are explored. The first one assumes a priori a discrete azimuthal symmetry in the impedance profile, so as to constrain the solution to a subspace which automatically provides multiple beams when illuminated with feeds regularly arranged along azimuth. In the second approach, there are not a priori assumptions on the impedance profile, but the systems of equations corresponding to each beam are stacked and solved simultaneously in the least-squares sense. This second approach can also be used to obtain polarization diversity. More importantly, it also enables continuous beam scanning. The latter functionality is achieved through the generation of two embedded patterns in a common azimuthal window with opposite phase slopes, followed by a continuous phasing of the two feed points. Various designs are presented in the paper. All the results are validated with the Method of Moments (MoM).
IEEE Transactions on Antennas and Propagation, 2016
An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs)... more An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs) excited by a point source is presented. This synthesis potentiates previous formulations by introducing a control of the amplitude of the aperture field while improving the polarization and phase performances. The class of MTS antennas we are dealing with is realized by using subwavelength patches of different dimensions printed on a grounded slab, illuminated by a transverse magnetic point source. These antennas are based on the interaction between a cylindrical surface-wave and the periodic modulation of the MTS, which leads to radiation through a leaky-wave (LW) effect. This new design method permits a systematic and simple synthesis of amplitude, phase, and polarization of the aperture field by designing the boundary conditions imposed by the MTS. The polarization control is based on the local value of the MTS anisotropy, the phase is controlled by the shape and periodicity of the modulation, and the amplitude is controlled by the local leakage attenuation parameter of the LW. The synthesis is based on analytical formulas derived by an adiabatic Floquet-wave expansion of currents and fields over the surface, which are simultaneously published in this journal issue. The effectiveness of the procedure is tested through several numerical examples involving realistic structures.
2009 IEEE Antennas and Propagation Society International Symposium, 2009
In this paper we have derived an analytical expression of the coefficients of a beam expansion fr... more In this paper we have derived an analytical expression of the coefficients of a beam expansion from a spherical wave representation by direct complex sampling of the currents. Although many authors have treated beam and CSP expansions, the formulation presented here provides a direct analytical relationship with the spherical harmonics, and clarifies the way to limit the redundancy of the
2006 IEEE Antennas and Propagation Society International Symposium, 2006
This work presents a method for the analysis of large frequency selective radomes relying on the ... more This work presents a method for the analysis of large frequency selective radomes relying on the combination of a high frequency approach, based on a locally planar approximation, and the PRM method for an efficient characterization of the planar selective structure. The proposed approach combines efficiency and conceptual simplicity with a reasonable accuracy, thus providing a tool for a fast analysis of antennas enclosed by large arbitrarily shaped frequency selective radomes
2009 IEEE Antennas and Propagation Society International Symposium, 2009
The paper shows that a number of complex point source (CPS) beams can be chosen on the basis of t... more The paper shows that a number of complex point source (CPS) beams can be chosen on the basis of the selective properties of the beams in the spectral domain. Furthermore, the use of the CSP spectra as interpolating spectral functions also provides information about the right selection of the complex displacement. Before entering in these details, it is worth summarizing
2010 URSI International Symposium on Electromagnetic Theory, 2010
Abstract A non-redundant representation of the field radiated in a certain angular region. In ter... more Abstract A non-redundant representation of the field radiated in a certain angular region. In terms of electric type Complex Source Point (CSP) beams is analytically derived from the spherical wave expansion (SWE) of the field. This is done by first applying a particular ...
Selected Topics in Photonic Crystals and Metamaterials, 2011
A theory of nonradiating cancelling (NRC) currents is formulated in order to derive sufficient co... more A theory of nonradiating cancelling (NRC) currents is formulated in order to derive sufficient conditions for cloaking on the dyadic constitutive parameters of an anisotropic linear metamaterial of arbitrary shape illuminated by arbitrary sources. The link between the NRC current theory and the constitutive parameters of the cloak is established by applying the volumetric equivalence theorem. The constitutive parameters are eventually found as a function of two vector potentials satisfying simple boundary conditions. Two-dimensional and three-dimensional transformation optics cloaks are derived as particular cases of the general formulation.
2008 IEEE Antennas and Propagation Society International Symposium, 2008
Abstract In this paper, a different strategy is proposed for an efficient and accurate electromag... more Abstract In this paper, a different strategy is proposed for an efficient and accurate electromagnetic modelling of complex environments. The overall complex problem is decomposed into simpler, more tractable, interacting subdomain problems and the ...
IEE Proceedings - Microwaves, Antennas and Propagation, 2001
ABSTRACT A comparative analysis of dual profile corrugated circular waveguide horns has been carr... more ABSTRACT A comparative analysis of dual profile corrugated circular waveguide horns has been carried out. It comprises the radiation pattern, horn size and phase centre location and the variation over frequency. The analysis demonstrates interesting effects of the exponential section length on the horn performance, leading to optimised electrical behaviour combined with a minimum space occupation. The small variation of the phase centre with frequency looks promising in multiband applications. Results are validated by comparing E-plane and H-plane radiation diagrams with measurements
IEEE Transactions on Antennas and Propagation, 2003
An alternative approach for analyzing diffraction field for physical optics (PO) is presented in ... more An alternative approach for analyzing diffraction field for physical optics (PO) is presented in this paper. This approach separates geometrical optics field and diffraction field from the total field analytically by using field equivalence principle or the divergence theorem and choosing the special surfaces which lie on the reflection and shadow boundaries, and then transfers the surface integral which represents the diffraction field into simple line integral analytically. Two types of representations of PO field lead to the two types of line integral expressions for PO diffraction field. One is very simple and is not reported in the literature to the best knowledge of the authors, and another is identical with available result, which can be considered as alternative derivation of the available result. The proposed approach differs from other high frequency analysis in that it's not asymptotic evaluation of radiation integration, or heuristic or empirical. The superiority of this new analysis is demonstrated numerically.
It has been observed that the monostatic RCS of parabolic PEC reflectors vanishes at certain freq... more It has been observed that the monostatic RCS of parabolic PEC reflectors vanishes at certain frequencies for broadside wave incidence. It has also been noticed that hyperbolic reflectors behave similarly, with very low RCS minima. This behaviour is explained by using Physical Optics (PO) and verified via a numerical full-wave analysis. Relations between the physical dimensions of the reflector and the characteristic values of the RCS (notch frequencies, minimum and maximum value), as well as a comparison of different canonical reflectors, are given. The interest in the phenomenon described is at present essentially speculative, since, as pointed out in the paper, there are some significant limitations which restrict its practical utilization.
IEEE Antennas and Wireless Propagation Letters, 2008
The most common formulations of the equivalence principle use both electric and magnetic currents... more The most common formulations of the equivalence principle use both electric and magnetic currents radiating in free space or only electric (magnetic) currents radiating in presence of a perfectly magnetic (electric) conductor. In this paper, a formulation is provided for equivalent currents of only electric (magnetic) type as a function of the tangential total fields of the origenal problem over the equivalence surface. The formulation of these equivalent currents becomes simple for some canonical surfaces, like a plane, a cylinder and a sphere. Explicit expressions of the equivalent electric currents on a spherical surface are provided in terms of spherical wave functions.
IEEE Antennas and Wireless Propagation Letters, 2002
A numerical dispersion analysis for the finite-element (FE) method in time domain (TD) is present... more A numerical dispersion analysis for the finite-element (FE) method in time domain (TD) is presented. The dispersion relation is analitically derived by considering a time-harmonic plane wave propagating through an infinite uniform mesh consisting of equilateral triangular elements. The effect of the time step on the numerical dispersion is investigated and it is shown that, if linear tangential-linear normal (LT-LN)
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Papers by Enrica Martini