Frequency dependence of correlation coefficients in ultra wideband antenna arrays

In order to optimize the performance of multi-antenna systems for communications applications it is desirable to have little correlation between the signals at the different receiving antennas. This can be achieved by choosing appropriate antenna characteristics and positions. For ultra wideband (UWB) applications this task is even more challenging, since correlation coefficients are dependent on frequency. This paper presents an investigation of the frequency dependence of the correlation coefficients of a linear antenna array in an UWB indoor propagation scenario. The investigated array itself consists of omni-directional elements. Thus only the correlation behaviour that is introduced by the propagation channel is regarded. It turns out from the conducted simulations that the correlation coefficients are highly altering with frequency and distance of the antennas. Furthermore, they severely depend on the position of the array inside the room. The simulation results show that, even if omni-directional antenna elements are used, with a dedicated placement of the antenna array pretty low correlation coefficients can be obtained over the entire frequency range regulated by the FCC for UWB applications.