Assessment and optimization of electromagnetic performance of low-frequency antenna arrays (SKA) by means of numerical methods

An overview of array advantages at low frequencies, as well as the SKA current design and implementation status comprise Chapter 1. The numerical EM methods used throughout the various analyses are outlined in Chapter 2, while SKALA4.1, the SKA-Low array element, is simulated using three different approaches: the Method of Moments, the Characteristic Modes Analysis and a dipole array simplified model. Spurious narrow-band phenomena relating to the log-periodic nature of SKALA4.1 are analysed in Chapter 3, where a dipole RLC loading method is proposed as a remedy. In Chapter 4, the ground plane is included in array simulations and its diffraction effects are quantified; a grid mesh analysis is also performed and compared to the solid plane simulations. Finally, in Chapter 5, mutual coupling between pairs of antennas is examined probing a first-order coupling framework, while mitigation strategies of the strong coupling features are tested with the two SKALA4.1 antennas. In the addendum of this thesis, the antenna used for the Large Experiment to detect the Dark Ages (LEDA) is simulated on various platforms of soil volume and ground plane surface. The antenna spectral response is in this case tested in greater rigor by examining a correction factor taking into account the sky brightness temperature; useful conclusions are drawn on the antenna beam requirements of such 21 cm global signal cosmology experiments. An array of such antennas known as the Long Wavelength Array (LWA) is also treated focusing on the mutual coupling effects.