An active radio-frequency (RF) sensing technology for determining the relative and/or absolute state (e.g., position, velocity, and/or acceleration) of a target object (e.g., a person, a car, a truck a lamp post, a utility pole, a building) is described. The sensors described herein operate in the Terahertz band (300 GHz to 3 THz). An active RF sensing device comprises a substrate and first and second semiconductor dies mounted on the substrate. The first semiconductor die has an RF transmit antenna array integrated thereon, and the transmit antenna array comprises a first plurality of RF antennas configured to generate an RF signals having frequency content in the 300 GHz-3 THz band. The second semiconductor die has an RF receive antenna array integrated thereon, and the receive antenna array comprises a second plurality of RF antennas configured to receive RF signals having frequency content in the 300 GHz-3 THz band.