MIMO antenna concept based on Characteristic Modes for indoor base stations

In this paper we present a design method for a multi-mode MIMO (Multiple Input Multiple Output) array, to be used in an indoor base station. The underlying concept is based on the TCM (Theory of Characteristic Modes) and is realized in an EM-simulator using 9 single antenna elements combined in a 3×3 antenna array. The excitation of the modes with low eigenvalues on each element is realized by three sets of slots at predefined positions on a PCB (Printed Circuit Board). These selective excitations on each antenna element result in an excitation of four current distributions and care for a low mutual coupling on the terminal itself. Combining these single elements in the 3×3 antenna array a decoupled 36-Port antenna system can be achieved. The results of the simulations show that all 36 antenna ports operate in the EU-UWB band and cover the frequency range of 5.725GHz-5.85 GHz, including the IEEE 802.1ac standard. This design method for a multi-mode MIMO antenna system is a straight forward application of the TCM and is therefore of general interest.