Fast postprocessing techniques for advanced spherical near-field measurements

• Autores: Fernando Rodríguez Varela
• Directores de la Tesis: Belén Galocha Iragüen (dir. tes.)
• Lectura: En la Universidad Politécnica de Madrid ( España ) en 2021
• Idioma: español
• Materias:
  • Física
    • Electromagnetismo
      • Ondas electromagnéticas
    • Física teórica
      • Radiación (electromagnética)
  • Ciencias tecnológicas
    • Tecnología electrónica
      • Antenas
• Enlaces
  • Tesis en acceso abierto en: Archivo Digital UPM
• Resumen

  • Spherical near-field measurements are a set of well-established techniques for accurate antenna testing. By scanning the near-field with an auxiliary probe over a spherical surface enclosing the antenna under test (AUT) and applying postprocessing techniques, its radiation pattern can be obtained with very low uncertainty. This considerably increases the measurement time compared with far-field or quasi-far-field approaches and imposes a series of constraints in terms of AUT-probe phase coherence and the number of sampling points, as well as its grid distribution. Such requirements may lead to longer, more expensive, or impractical measurement processes. The development of advanced postprocessing techniques allows to relax these constraints, to maximize the efficiency of modern antenna measurement facilities.

    After introducing the basic theory of spherical near-field to far-field transformation, as well as the state-of-the-art algorithms and challenges, this thesis contributes with a series of innovative techniques for spherical near-field postprocessing in different scenarios. Three different challenging applications are considered:

    -Reduction of measurement samples to minimize measurement time: two different techniques which exploit the radiation properties of pencil beam and offset-mounted antennas will be presented.

    -Non-uniform grids and arbitrary surfaces: the use of scanning grids different from equiangular, as well as the generalization of near-field measurements to arbitrary surfaces are of high interest to increase the flexibility of the measurement process. For this application, two efficient techniques are proposed and investigated.

    -Phaseless measurements: working with amplitude-only data facilitates high-frequency measurements and may avoid the need of expensive radiofrequency equipment. Phase retrieval techniques will be investigated to allow the postprocessing in these scenarios.

    The common goal of all the introduced algorithms is to retrieve the Spherical Wave Expansion (SWE) of the AUT minimizing the required near-field information and computational resources. Once the SWE is obtained all radiation characteristics of the AUT, including the radiation pattern can be derived straightforwardly.

    With the investigation results and algorithms introduced in this thesis, antenna measurement facilities, such as the one at Universidad Politécnica de Madrid, can benefit incorporating the derived knowledge. Practical examples with measured near-field data have been carried out proving that all developed techniques can be implemented in the postprocessing software to allow for advanced measurements. In addition, new lines of research are opened for further improvement of the introduced contributions.