Miniaturized Circular Polarized Antenna with Optimized Multipath Suppression for Indoor Positioning Systems

The development of Indoor Positioning Systems (IPS) promises an extension of satellite navigation to indoor scenarios with significantly better spatial and temporal resolution [1] . We have developed a time difference of arrival (TDoA) based IPS approach operating at 5.8 GHz ISM band featuring Frequency Division Multiplexing (FDM) principals with minimized channel offsets of the up to eight base stations placed around the monitoring space. Mobile devices analyze these signals for the position estimation. Due to the high number of scattering objects in indoor scenarios, one major challenge here is the multipath propagation superimposing line of sight signals and thus disturbing the extraction of the TDoA information. Using circular polarized RF signals aims at minimizing this interference by switching the polarization after reflection. This article introduces the antenna developed for the receiving mobile devices. For applications as human motion analysis, the mobile devices have to be small, lightweight and should favor a central reference position to make the device symmetrically rotatable around its center of reception. A circularly polarized annular ring patch antenna fulfills these requirements [2] . The chosen design realizes a matched right-hand circular polarized (RHCP) antenna. Employing a ceramic (Y 2 0 3 partially stabilized Zirconia) with high permittivity ( ε r = 29) leads to considerable minimal dimensions ( Fig. 1a ) in comparison to monopole and other patch antennas [3] . We made use of the EMPro software tool from Keysight to optimize the antenna dimensions and performance by simulation.