  Coordination of multi-robot systems require some form of localization between
agents, but most methods today rely on some external infrastructure. Ultra Wide
Band (UWB) sensing has gained popularity in relative localization applications,
and we see many implementations that use cooperative agents augmenting UWB
range measurements with other sensing modalities (e.g., ViO, IMU, VSLAM) for
infrastructure-free relative localization. A lesser researched option is using
Angle of Arrival (AoA) readings obtained from UWB Antenna pairs to perform
relative localization. In this paper we present a UWB platform called ReLoki
that can be used for ranging and AoA-based relative localization in~3D. ReLoki
enables any message sent from a transmitting agent to be localized by using a
Regular Tetrahedral Antenna Array (RTA). As a full scale proof of concept, we
deploy ReLoki on a 3-robot system and compare its performance in terms of
accuracy and speed with prior methods.
