Pareyson y «el mal (la nada) en Dios». Notas para una comparación con la metafísica clásica

En su obra póstuma Ontologia della libertà, Luigi Pareyson cuestiona el problema del mal no tanto a partir de la libertad humana, sino en relación con ese "abismo de libertad" que sería la realidad divina. Desarrollando un pensamiento que presenta evidentes analogías con el del último Schelling, Pareyson concibe la "nada" como un momento del Absoluto, que se determina según una dialéctica de lo positivo y lo negativo dentro de la cual encuentran su lugar el origen del ser y la posibilidad de la existencia del mal. En este trabajo se exponen las razones por las que esta crítica a cualquier teodicea posible es insostenible -incluso antes de su concepción de la naturaleza del mal - en sus mismos "fundamentos" lógico-metafísicos, o en su intento de liberarse del discurso metafísico sobre Dios

Gain antenna measurement using single cut near field measurements

Some antennas require rapid validation at a reduced measurement distance while maintaining sufficient accuracy in the determination of pertinent antenna parameters such as gain. In particular, for cellular base station antennas in production phase the measurement time can be a limitation. In these cases, a rapid check of the radiation performance in the two main planes is sufficient. Other examples are phase arrays with high degree of steering that would require considerable measurement time for characterizing all steering positions. This paper presents a near-field antenna test procedure providing single or double main plane patterns including the gain. The procedure is applicable to antennas, with separable excitation in the two main planes. The test set-up is based on an azimuth positioner and near to far-field transformation based on expansion in cylindrical modes. The paper shows results for gain measurements. Near to far-field transformation is performed using the cylindrical modes expansion assuming a zero-height cylinder. This allows the use of a FFT in the calculation of the far field pattern including probe correction. In the case of gain, the near to far-field transformation factor is calculated for bore sight direction, taking advantage of the separable excitation properties of the antenna. This factor is used in the gain calculation by comparison technique

Time and spatial filtering for echo reduction in antenna measurements

During the last years, new algorithms, based on time filtering, spatial or modal filtering, have been designed for echo reduction techniques applied to antenna measurements. These algorithms have been used for different applications where the effect of the echoes is important, as far field system, VHF or UHF applications, automotive systems, small antennas, etc. The authors, in previous papers, have analysed the effect of different algorithms: time filtering (fft, non uniform dft or matrix pencial), modal filtering based on Spherical modes (MV-Echo) and spatial filtering based on Integral Equations (Insight) and holographic techniques (fft and dft) to cancel the effect of the reflections. This comparison has been applied to the measurements of a dipole antenna (SD1900) using a StarLab system. It is observed that each of the algorithms is better for different situations, depending on the source of the echo. For instance, time filtering techniques are good for reflections coming from different distances with respect the direct ray, but not so good for close reflections. In addition hey need a large frequency band to work properly. Spatial algorithms can correct the effect of positioners or other structures close to the antenna under test, but they are better for planar near field acquisitions and worse for classical single probe spherical near field where the antenna is rotated and probe is fixed (e.g. roll-over-azimuths systems). Moreover, they require extra information of the AUT geometry. This paper presents first a comparison of each algorithm and then, a combination of time and spatial techniques based on uniform or non-uniform DFT to take advantage of the benefits of each algorithm for different origins of the reflections

Combination of time and spatial filtering to improve echo reduction in antenna measurements

Different research groups have been working during the last years in different echo reduction techniques applied to antenna measurements, based on spatial, modal or time filtering. Some applications where these methods are usually employed are: outdoor systems, for HF or VHF frequency systems or for small measurement systems where the anechoic material is only placed in front of the AUT. This paper analyzes the measurements of a dipole antenna (SD1900) using a StarLab system and the application of the different algorithms. It is observed that each of the algorithms is better for different situations, depending for instance on the angular value of the pattern. Finally, a combination of different methods in a smart way improve the results of the post processing with respect each independent method

Comparison of echo reduction techniques for one-single cut antenna measurements

This paper presents a comparison between two different echo reduction techniques applied to one-single cut antenna measurements. These techniques are based on modal filtering and time filtering. The first technique uses a postprocessing of the far field one-single cut so as to obtain a modal expansion of cylindrical modes and to cancel the effect of spurious signals. The second one is based on filtering echoes out in time domain by applying a Fourier Transform to get a signal in which some spurious contributions can be filtered out. Such techniques are applied on the single cut measurements of a wideband horn (MVI SH2000) performed in a semi-anechoic chamber and on the measurements of a dipole (MVI SD1900) performed in a MVG spherical multi-probe system (StarLab). A smart combination of both methods is also applied in order to improve the results of the post processing with respect each different method

Analysis and suppression of reflections in far-field antenna measurement ranges

This paper presents the analysis of the reflections in two kind of spherical far field ranges: one if the classical acquisition where the AUT is rotated and the second one corresponds to the systems where the AUT is fixed and the antenna probe is rotated. In large far field systems this is not possible, but this can be used to the measurement of small antennas, for instance, with the SATIMO StarGate system. In both cases, it is assumed that only one frequency is acquired and the results should be improved cut by cut, in order not to lose the advantages or far field measurements. Finally, some practical results are studied using measurements of one antenna in the outdoor far field facility of LIT INPE in Brazil

A reflection suppression technique for far field antenna measurements

This paper presents a reflection suppression technique for far field antenna measurements. The technique is based on a source reconstruction over a surface greater than the antenna itself. To be able to perform the reflection construction the next steps are required: the complete far field antenna pattern is obtained through interpolation of the acquired cuts, the currents are obtained through a holographic technique, the field out of the antenna area is filtered, and the pattern is reconstructed. The algorithm is used with measurements in the LEHA-UPM antenna measurement facilities and in the outdoor far field facility of LIT INPE in Brazil

A fast single cut spherical near-field-to-far-field transformation using cylindrical modes

A fast spherical near-field to far-field transformation using single cuts is introduced in this paper. It is based on calculating the Cylindrical Modal Coefficients of each individual near-field ring and processing them independently, considering them as cylinders of zero height and applying probe correction. The reconstruction of each far-field cut is obtained through an inverse Fast Fourier Transform. This procedure provides the opportunity to perform real time transformations due to its low acquisition and processing time. It is a useful tool for applications which do not require a full or accurate characterization, such as measuring the main patterns of an antenna or its most important parameters (peak gain, beam width, side lobe level, etc.)

Comparison and application of different echo reduction techniques in antenna measurement

During the last years, different methods for improving the quality of the antenna measurements results have been developed, in particular for echo reduction. This paper is a common research work between Universidad Politécnica de Madrid and Microwave Vision Group whose objective is the comparison of different echo reduction techniques in order to be able to explote the advantages of each one in antenna measurements applications. In particular, these techniques are specially important for outdoor antenna measurement systems, for systems as the StarLab (where the measurement equipement is placed without full coverage of absorbing material) or for measurements at lower frequencies where the performance of the absorbing material is not good enough. These techniques are based on spatial filtering, modal filtering and time gating techniques. The paper analyzes different approaches: in particular for spatial filtering, holographic techniques [1] and source reconstruction based on integral equations [2] are analyzed. In the first case, the field is back propagated to a large planar surface containing the antenna under test, and the fields out of the antenna area are filtered out. The main advantage is the very small time required for the transformation, while the disadvantages are focused on the specific applications for planar antennas and the need of geometrical information to improve the results. The second algorithm, based on source reconstruction using integral equation (in particular the authors analyzed MVG INSIGHT© algorithm). The main disadvantage is the time consumption, although the results are better accurate than the previous one. In the case of modal filtering, there are different approaches, with similar theoretical basis. This paper uses the approach included in MV-Echo© [3] for the cancellation of the echos based on the spherical modes decomposition of the radiated field. The last group of algorithms are based on time filtering. In particular FFT [4], Matrix Pencil method [5] and non uniform DFT are used. In all the cases, the results are similar. The first algortihm requires uniformly frequency spaced samples (not always available) but it is faster. In these three cases, the main disadvantage is the number of frequencies (and step) required for having a good echo reduction. The different algorithms have been applied to the measurement of a dipole antenna (SD1900) in the MVI StarLab System. Results show that depending on the angular range of the pattern the improvements are better or worst using any of the methods. Results will be shown in the final paper or presentation