: Basic technological work done on a 20/30 GHz L-SAT propagation experiment receiver is presented... more : Basic technological work done on a 20/30 GHz L-SAT propagation experiment receiver is presented, covering receiver configuration, measurement systems, Gunn-diode oscillators, fin-line transitions and cylindrical near field antenna measurement systems. (Author)
A novel integral formulation of the Mea- sured Equation of Invariance method is derived from the ... more A novel integral formulation of the Mea- sured Equation of Invariance method is derived from the reciprocity theorem. This formulation uses the electric and magnetic Green's functions of the envi- ronment to obtain a matrix equation for the induced surface current with the same number of unknowns as the conventional Boundary Element - Method of Moments (BE-MOM) approach. However, the matrix that must be inverted in the new formulation is sparse and circulant, with only three non-zero elements per row. Sample results for two-dimensional TM and TE problems with perfectly conducting scatterers show enormous CPU time and memory savings over the conventional BEM-MOM approach. The new formula- tion has important advantages over the original finite difference formulation of MEI, but also shares some of its limitations.
In the study of electromagnetic radiation effects over dielectric bodies, effective numerical met... more In the study of electromagnetic radiation effects over dielectric bodies, effective numerical methods are needed. At present, there is a lack of tools for measuring this effects and due to the huge growth of microwave devices, like cellular radio telephones working close to the human body, it is necessary to develop accurate numerical methods for evaluating those effects. One of
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010), 1999
This paper reviews the graphical processing approach (Greco) to compute high-frequency radar cros... more This paper reviews the graphical processing approach (Greco) to compute high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. Targets are modeled with a solid modeling CAD package using a parametric surface approach. High-frequency RCS of perfectly conducting objects is obtained through physical optics, elementary edge waves and ray-tracing methods. An image of the target at the workstation screen is processed to obtain unit normals, radius of curvature and orientation of illuminated surfaces and edges. The result is a very fast and efficient code for RCS computation of complex targets.
The integral equation MEI IE-MEI is a new, sparse matrix formulation of the boundary-element meth... more The integral equation MEI IE-MEI is a new, sparse matrix formulation of the boundary-element method, which is particularly well suited for large con¨ex scatterers. In this Letter we explain why the original implementation of IE-MEI fails for large conca¨e objects and propose a remedy.
IEEE Antennas and Propagation Society International Symposium 1992 Digest, 1992
An iterative spectral propagation algorithm is developed which introduces new features that impro... more An iterative spectral propagation algorithm is developed which introduces new features that improve the numerical efficiency and accuracy of the spectral iteration technique and the spectral incremental propagation procedure. The new spectral algorithm is particularly useful for analyzing closed problems where the boundary structure is too large for low-frequency matrix methods and too complex for high-frequency approximations. The scope of application includes the radar cross section of cavities, waveguide discontinuities and filters, and conformed or corrugated horn antenna analysis. The method is also valid for scattering problems in free space, but the continuous spectrum of nonperiodic fields together with the periodicity of the discrete Fourier transform require a very high number of field samples. For that reason, the efficiency of the algorithm may be worse than that of matrix methods for very complex scatterers and worse than that of high-frequency methods for large and simple objects. The main drawback is that boundary conditions are restricted to perfect electric or magnetic conductors, so that electric loading cannot be considered
A novel algorithm designed to compute efficiently and accurately the HF electromagnetic scatterin... more A novel algorithm designed to compute efficiently and accurately the HF electromagnetic scattering from open-ended waveguide cavities is presented. The cavity is converted into a stepped-waveguide model so that the field spectrums are propagated, forward and backward, along each waveguide section. As boundary conditions for perfect electric conductors are applied via image theory, they are of local nature and take into account only the first order interactions between each pair of waveguide sections. Accordingly, additional forward-backward iterations must be performed if multiple interactions are to be taken into account. Finally, the RCS due to the interior irradiation is calculated by a Kirchhoff-based aperture integral. Good agreement with Method of Moments and Hybrid Modal solutions is found, as well as with experimental data, for 2-D and 3-D cavities.
Ultrawide-band tomography, producing images that show slices of objects, is less harmful than x-r... more Ultrawide-band tomography, producing images that show slices of objects, is less harmful than x-rays and can provide useful, high resolution images.
Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can ... more Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can provide unusual electromagnetic properties, such as the dual PMC/PEC behavior, when used as reflectors. This property has been assessed and tested with the design and fabrication of a one-layer spiral AMC slab. Moreover, two bidirectional AMC surfaces have also been designed and measured. These
IEEE Transactions on Microwave Theory and Techniques, 1991
A prototype imaging system for active microwave tomography using cylindrical geometry has been de... more A prototype imaging system for active microwave tomography using cylindrical geometry has been developed, making is possible to obtain images of the dielectric properties of biological targets at 2.45 GHz. The system requires no mechanical movements to illuminate the body from multiple directions (views) and measure the scattered fields. In this way a complete data set consisting in 64 views is acquired in 3 s using low-power illumination. The system is described, including images obtained with biological phantoms and actual bodies.
: Basic technological work done on a 20/30 GHz L-SAT propagation experiment receiver is presented... more : Basic technological work done on a 20/30 GHz L-SAT propagation experiment receiver is presented, covering receiver configuration, measurement systems, Gunn-diode oscillators, fin-line transitions and cylindrical near field antenna measurement systems. (Author)
A novel integral formulation of the Mea- sured Equation of Invariance method is derived from the ... more A novel integral formulation of the Mea- sured Equation of Invariance method is derived from the reciprocity theorem. This formulation uses the electric and magnetic Green's functions of the envi- ronment to obtain a matrix equation for the induced surface current with the same number of unknowns as the conventional Boundary Element - Method of Moments (BE-MOM) approach. However, the matrix that must be inverted in the new formulation is sparse and circulant, with only three non-zero elements per row. Sample results for two-dimensional TM and TE problems with perfectly conducting scatterers show enormous CPU time and memory savings over the conventional BEM-MOM approach. The new formula- tion has important advantages over the original finite difference formulation of MEI, but also shares some of its limitations.
In the study of electromagnetic radiation effects over dielectric bodies, effective numerical met... more In the study of electromagnetic radiation effects over dielectric bodies, effective numerical methods are needed. At present, there is a lack of tools for measuring this effects and due to the huge growth of microwave devices, like cellular radio telephones working close to the human body, it is necessary to develop accurate numerical methods for evaluating those effects. One of
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010), 1999
This paper reviews the graphical processing approach (Greco) to compute high-frequency radar cros... more This paper reviews the graphical processing approach (Greco) to compute high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. Targets are modeled with a solid modeling CAD package using a parametric surface approach. High-frequency RCS of perfectly conducting objects is obtained through physical optics, elementary edge waves and ray-tracing methods. An image of the target at the workstation screen is processed to obtain unit normals, radius of curvature and orientation of illuminated surfaces and edges. The result is a very fast and efficient code for RCS computation of complex targets.
The integral equation MEI IE-MEI is a new, sparse matrix formulation of the boundary-element meth... more The integral equation MEI IE-MEI is a new, sparse matrix formulation of the boundary-element method, which is particularly well suited for large con¨ex scatterers. In this Letter we explain why the original implementation of IE-MEI fails for large conca¨e objects and propose a remedy.
IEEE Antennas and Propagation Society International Symposium 1992 Digest, 1992
An iterative spectral propagation algorithm is developed which introduces new features that impro... more An iterative spectral propagation algorithm is developed which introduces new features that improve the numerical efficiency and accuracy of the spectral iteration technique and the spectral incremental propagation procedure. The new spectral algorithm is particularly useful for analyzing closed problems where the boundary structure is too large for low-frequency matrix methods and too complex for high-frequency approximations. The scope of application includes the radar cross section of cavities, waveguide discontinuities and filters, and conformed or corrugated horn antenna analysis. The method is also valid for scattering problems in free space, but the continuous spectrum of nonperiodic fields together with the periodicity of the discrete Fourier transform require a very high number of field samples. For that reason, the efficiency of the algorithm may be worse than that of matrix methods for very complex scatterers and worse than that of high-frequency methods for large and simple objects. The main drawback is that boundary conditions are restricted to perfect electric or magnetic conductors, so that electric loading cannot be considered
A novel algorithm designed to compute efficiently and accurately the HF electromagnetic scatterin... more A novel algorithm designed to compute efficiently and accurately the HF electromagnetic scattering from open-ended waveguide cavities is presented. The cavity is converted into a stepped-waveguide model so that the field spectrums are propagated, forward and backward, along each waveguide section. As boundary conditions for perfect electric conductors are applied via image theory, they are of local nature and take into account only the first order interactions between each pair of waveguide sections. Accordingly, additional forward-backward iterations must be performed if multiple interactions are to be taken into account. Finally, the RCS due to the interior irradiation is calculated by a Kirchhoff-based aperture integral. Good agreement with Method of Moments and Hybrid Modal solutions is found, as well as with experimental data, for 2-D and 3-D cavities.
Ultrawide-band tomography, producing images that show slices of objects, is less harmful than x-r... more Ultrawide-band tomography, producing images that show slices of objects, is less harmful than x-rays and can provide useful, high resolution images.
Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can ... more Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can provide unusual electromagnetic properties, such as the dual PMC/PEC behavior, when used as reflectors. This property has been assessed and tested with the design and fabrication of a one-layer spiral AMC slab. Moreover, two bidirectional AMC surfaces have also been designed and measured. These
IEEE Transactions on Microwave Theory and Techniques, 1991
A prototype imaging system for active microwave tomography using cylindrical geometry has been de... more A prototype imaging system for active microwave tomography using cylindrical geometry has been developed, making is possible to obtain images of the dielectric properties of biological targets at 2.45 GHz. The system requires no mechanical movements to illuminate the body from multiple directions (views) and measure the scattered fields. In this way a complete data set consisting in 64 views is acquired in 3 s using low-power illumination. The system is described, including images obtained with biological phantoms and actual bodies.
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Papers by A. Cardama