This chapter presents the ARTK: antenna-array aided real time-kinematic positioning. It explores the potential benefits of antenna-array aided precise point positioning to the long-range RTK, which is referred to as array-aided RTK. We formulate the platform array model and show how its data can be reduced. Then, three different ionosphere-weighted differential array models are described, and closed-form formulae for their ambiguity variance matrices are presented. These matrices determine the success rates for estimating the integer ambiguities. Finally, the ARTK model for platforms is outlined, where static and kinematic experiments are also presented.