1 Introduction
Ultra-wideband (UWB) technology together with Time of Flight (ToF) based localization techniques are often used to realize indoor positioning systems. Huge bandwidth of UWB signals results in fine time resolution allowing precise time estimations even in indoor environment [1], [2], where severe multipath propagation is present. An important part of UWB based localization systems are the utilized antennas. UWB antennas often lead to significant signal distortions [3], which generally is also Angle of Arrival (AoA) dependent affecting a communication system or resulting in ToF estimation errors. As will be illustrated in this paper this antenna induced error can lead to a significant impact on the performance of the system, which is critical for special cases of TDoA based AoA estimation technique with closely spaced receiving antennas. Only the case of Line of Sight (LoS) is considered in the paper. It is also assumed that reflections can be separated from the direct signal path (DP), which is often assumed in UWB-based localization.