Application of sources reconstruction techniques: Theory and practical results.

In this paper, four new applications of sources reconstruction techniques (also called diagnostic techniques) are presented. First of all, the important information of such techniques will be mentioned, seeing that they are a tool to obtain the extremely near field from the measured data. Depending on the region where these data are taken (near field or far field), the reconstruction method will be different. Also, all of them may be classified in other two groups depending on its features: Integral Equation Methods (IEM) or Modal Expansion Methods. Classical applications of such techniques are errors detection, like phase errors in arrays or conformai errors in reflectors, therefore, they constitute an important antenna design tool. But also and it has been said, they can be used as the basis to other applications whose aim is to improve the measurement results in anechoic chambers or non anechoic environments. Here, four of them are presented, being the reflection cancelling, the detection of unwanted radiation points, the truncation error reduction in planar or cylindrical near-field and the noise reduction

Nuevo Método de Mejora de la Relación Señal a Ruido en Resultados de Medidas en Campo Próximo Plano.

A new method to reduce the noise power in the far field pattern obtained from a planar near-field measurement is proposed. The recorded data in such measurement are assumed to be corrupted with white Gaussian and space stationary noise, being the receiver additive noise a possible source for that noise. Back-propagating the field from the scan plane to the antenna under test (AUT) plane and applying a proper spatial filtering, a great improvement of the signal to noise ratio is achieved. Several examples both from simulations and measurements are presented in order to validate the theoretical analysi

Novel method to improve the signal-to-noise ratio in the far-field results obtained from planar near-field measurements

A method to reduce the noise power in far-field pattern without modifying the desired signal is proposed. Therefore, an important signal-to-noise ratio improvement may be achieved. The method is used when the antenna measurement is performed in planar near-field, where the recorded data are assumed to be corrupted with white Gaussian and space-stationary noise, because of the receiver additive noise. Back-propagating the measured field from the scan plane to the antenna under test (AUT) plane, the noise remains white Gaussian and space-stationary, whereas the desired field is theoretically concentrated in the aperture antenna. Thanks to this fact, a spatial filtering may be applied, cancelling the field which is located out of the AUT dimensions and which is only composed by noise. Next, a planar field to far-field transformation is carried out, achieving a great improvement compared to the pattern obtained directly from the measurement. To verify the effectiveness of the method, two examples will be presented using both simulated and measured near-field data

Definition of accurate reference pattern of the VAST12 antenna

In this paper, the DTU-ESA 12 GHz Validation Standard (VAST12) Antenna and a dedicated measurement campaign carried out in 2007-2008 for the definition of its accurate reference pattern are first described. Next, a comparison between the results from the three involved measurement facilities is presented. Then, an accurate reference pattern of the VAST12 antenna is formed by averaging the three results taking into account the estimated uncertainties of each result. Finally, the potential use of the reference pattern for benchmarking of antenna measurement facilities is outlined

Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna

In this paper, three possible approaches for definition of a highly accurate reference pattern of a reference antenna are described and their pros and contras are discussed. Following the most reliable approach, a dedicated measurement campaign was planned and carried out in 2007-2008 for definition of the highly accurate reference pattern of the VAST12 antenna. In planning the campaign, conclusions from the first comparison campaign with the VAST12 carried out within the ACE network in 2004-2005 were taken into account and these are also presented and discussed. Some typical measurement errors and uncertainties are listed and briefly discussed

Characterization of measurement systems through extensive measurement campaigns

Within the European Union network "Antenna Center of Excellence" – ACE (2004-2007), two intercomparison campaigns among different European measurement systems, using the 12 GHz Validation Standard (VAST12) antenna, were carried out. These campaigns are described in the companion paper “Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna”. The second campaign was performed by Technical University of Denmark (DTU) in Denmark, SAAB Microwave Systems in Sweden and Technical University of Madrid (UPM) in Spain. This campaign consisted of a large number of measurements with slightly different configurations in each of the three institutions (2 spherical near field systems and one compact range). The purpose of this paper is to evaluate the accuracy of the different facilities using this large number of acquisitions. The acquisitions were performed systematically varying in applied scanning scheme, measurement distances, signal level and so on. The results are analyzed by each institution combining the measurement results in near or far field and extracting from these measurements: a “best” pattern, an evaluation of possible sources of errors (i.e. reflections, mechanical and electrical uncertainties) and an estimation of the items of the uncertainty budget

Electrical and mechanical uncertainty study in cylindrical near field antenna measurement systems

In order to evaluate how mechanical or electrical errors may affect in the final results (i.e. radiation patterns, directivity, side lobe levels (SLL), beam width, maximum and null position…), an error simulator based on virtual acquisitions of the measurement of the radiation characteristics in a cylindrical near-field facility has been implemented [1], [2]. In this case, the Antenna Under Test (AUT) is modelled as an array of vertical dipoles and the probe is assumed to be a corrugated horn antenna. This tool allows simulating an acquisition containing mechanical errors – deterministic and random errors in the x-, yand z-position – and also electrical inaccuracies – such as phase errors or noise –. Then, after a near-to-far-field transformation [3], by comparing the results obtained in the ideal case and when including errors, the deviation produced can be estimated. As a result, through virtual simulations, it is possible to determine if the measurement accuracy requirements can be satisfied or not and the effect of the errors on the measurement results can be checked. This paper describes the error simulator implemented and the results achieved for some of the error sources considered for an L-band RADAR antennas in a 15 meters cylindrical near field system

Uncertainty simulator to evaluate the electrical and mechanical deviations in cylindrical near field antenna measurement systems

In order to evaluate how mechanical or electrical errors may affect in the final results (i.e. radiation patterns, directivity, side lobe levels (SLL), beam width, maximum and null position…), an error simulator based on virtual acquisitions of the measurement of the radiation characteristics in a cylindrical near-field facility has been implemented [1], [2]. In this case, the Antenna Under Test (AUT) is modelled as an array of vertical dipoles and the probe is assumed to be a corrugated horn antenna. This tool allows simulating an acquisition containing mechanical errors – deterministic and random errors in the x-, y- and z-position – and also electrical inaccuracies – such as phase errors or noise –. Then, after a near-to-far-field transformation [3], by comparing the results obtained in the ideal case and when including errors, the deviation produced can be estimated. As a result, through virtual simulations, it is possible to determine if the measurement accuracy requirements can be satisfied or not and the effect of the errors on the measurement results can be checked. This paper describes the error simulator implemented and the results achieved for some of the error sources considered for an L-band RADAR antennas in a 15 meters cylindrical near field syste