Jaime Laviada

Solution of Electrically Large Problems With Multilevel Characteristic Basis Functions

We present a multilevel version to the characteristic basis function method (CBFM). This technique extends the range of applicability of the conventional CBFM and allows a direct solution of problems even when they exceed 250,000 degrees of freedom. In this paper, it is shown how we can use the multilevel CBFM, which is a natural extension of the conventional approach and which saves both time and memory, and yet retains excellent accuracy in the computed far fields. Also, the adaptive cross algorithm is used for fast calculation of the interaction between the blocks in the process of generating the reduced matrix.

Synthesis of Passive-dipole Arrays with a Genetic-neural Hybrid Method

Neural networks and genetic algorithms are combined in a new hybrid technique able to perform synthesis tasks over passive-element antenna arrays, whose radiation pattern is defined by the coupling effects between the active and passive elements. The combination of both methods improves the results obtained using neural networks, also reducing the computation time required by genetic algorithms. Some significant results are presented.

Phaseless Synthetic Aperture Radar With Efficient Sampling for Broadband Near-Field Imaging: Theory and Validation

This paper presents a broadband and phaseless synthetic aperture radar (SAR) with efficient sampling. The design relies on a novel phaseless monostatic element comprising a transmitter and a receiver. This element, together with a computationally inexpensive algorithm, can retrieve the phase of the monostatic scattered field at all the working band except for two small safety margins at the lower and upper frequencies. Furthermore, the phase retrieval works independently of the transmitter/receiver position. Consequently, conventional approaches to reduce the number of monostatic acquisition points can be employed. Thus, the proposed strategy is suitable to implement either arrays that benefit from a reduced number of low-complexity elements or raster scan systems that benefit not only from the cost reduction of the scanning components but also from a remarkable speed-up due to the reduced number of acquisition points. Moreover, in contrast to other off-axis schemes, the proposed system does not require neither mechanical nor electrical phase shifting and, therefore, it can be directly adapted to a large number of frequency bands. The performance of the system is validated by simulation and measurement examples in the millimeter-wave band.

Genetic algorithms to optimise the time to make stock market investment

The application of Artificial Intelligence described in this article is intended to resolve the issue of speculation on the stock market. Genetic Algorithms is the technique that is used, with the article focusing on the different ways that chromosomes can be designed and on how the pertinent evaluation mechanism is established. The problem will be based on the speculation systems that are typical of Technical Analysis.

Realistic Antenna Array Synthesis in Complex Environments Using a MOM-SVR Approach

The Support Vector theory combined with antenna array modeling based on the Method of Moments is proposed to provide an accurate synthesis method able to solve problems specified in terms of a template or a mask, taking into account all the real properties of the radiating structure and its environment, such as coupling effects or the presence of an obstacle, and without the need of the measurement of training patterns. Illustrative results are presented.

Phaseless Antenna Measurement on Non-Redundant Sample Points Via Leith-Upatnieks Holography

A scheme for reducing the number of sample points in phaseless acquisition based on Leith-Upatnieks holography is presented. An appropriate choice of the phase of the reference field enables to drastically decrease the sampling rate by acquiring the so-called “reduced” field instead of the real radiated field. The reference phase changes are enabled by applying the recent developments on the synthesis of the reference wave. Moreover, optimal sampling interpolation can be applied to the retrieved field so that the real field can be computed at any point on the acquisition surface. The method is illustrated by means of multiple simulations for observation domains such as straight lines, azimuthal circles as well as for a plane-polar acquisition scheme.

Submillimeter-Wave Frequency Scanning System for Imaging Applications

A new submillimeter-wave imaging system based on the frequency scanning concept is presented. Using significantly less information than beam-steering techniques, frequency scanning-based imaging systems are able to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. Several strategies have been adopted to overcome the low dynamic range due to the propagation losses and non-specular reflection on the object-under-test. Moreover, the system is not only capable of detecting the placement of the objects, but also their profile. In this sense, an imaging application showing the system capabilities for the detection of objects concealed under clothes is presented. Results using 1-D FSAA allowing profile imaging are shown, proving the validity of the proposed system.

A novel phaseless frequency scanning based on indirect holography

A phase retrieval technique for multifrequency scattered field acquisition is presented in this paper. The proposed setup is based on indirect holography schemes so that it combines the desired signal with a known reference signal. The setup is used together with a two-dimensional frequency scanning (FS) antenna and, therefore, the positions of scatterers can be retrieved without the need of moving either the antenna or the objects.

Inverse Fast Multipole Method for Monostatic Imaging Applications

A 3-D imaging technique for monostatic radar cross section measurement is presented. The method is based on an existing formulation conceived for bistatic geometries which takes into account the scattered field polarization and is accelerated using the fast multipole method. The synthetic aperture radar (SAR) image processing includes acquired field, which is of interest for polarimetric SAR imaging. In addition, the proposed technique overcomes the limitation of fast-Fourier-transform-based inverse techniques on canonical domains (planar, cylindrical, and spherical). Validation with simulations and measurements is presented. Calculation time is also drastically reduced using graphics processing unit implementation.

Interferometric Technique With Nonredundant Sampling for Phaseless Inverse Scattering

A phaseless data acquisition applied on a reduced set of points is presented for inverse scattering problems. The setup is based on the Leith-Upatnieks holography with synthesized reference waves so that the phase of the reference wave can be adjusted to acquire the so-called “reduced field” instead of the regular field. Thus, nonregular sampling techniques can be applied resulting in strong reduction in the number of acquisition points. The technique is validated using simulation and measurement examples at microwave frequencies.