Mutual coupling effects and optimum architecture of a sparse antenna array

Abstract: The objective of this thesis is to investigate the performance of the EISCAT 3D Array antenna for dierent architectures and dierent types of elements. The thesis focuses on the type of element designed by Lulea Technical University and build by GELAB Company. Another objective is to nd the optimum architecture that will make the array meet the requirements of a 3D imaging radar and result in a minimum number of elements for achieving the performance goals set by the specications. The EISCAT 3D Array requires a high number of elements and this implies a high level of interaction between the elements, also known as mutual coupling. In order to simulate the performance of the array including the coupling, a program was written in MATLAB using an element radiation pattern simulated in NEC2. This pattern includes the mutual coupling eects of the single element designed by Lulea Technical University. A method called thinning is applied to reduce the number of elements and, consequently, the coupling. The results show that the thinning parameters change the performance of the array with a xed pattern. Increasing the number of elements, the key performance indicators (Directivity and Side lobe level) show an improvement. It was found that one of the thinning parameters, the design side lobe ratio, has more weight on the indicators. This parameter indicates the maximum level of the side lobe and for increasing values, the Directivity decreases but the Peak Side lobe improves to a higher level. The Average Side lobe level, however, decreases when the design side lobe ratio parameter increases. As a conclusion, it can be said that a thinned array with a circular aperture meets the requirements better than one with a square aperture. The circular aperture leads to improved results (higher Directivity) with less elements. Another important conclusion is that the directivity of the main beam and the side lobe level is strongly dependent on both the azimuthal and elevation angle. In order to fully understand the consequences of mutual coupling and thinning, a more in-depth investigation into all directions in the eld of view needs to be conducted before a nal decision on the element design can be made.