A radar device for measuring distance within short range is provided. The radar device has a first wave-detecting circuit for multiplying radio wave voltage being transmitted from a transmitting antenna by radio wave voltage being received by a receiving antenna, in addition, the device has a second wave-detecting circuit for multiplying radio wave voltage being transmitted from the transmitting antenna by radio wave voltage shifted by the shifting means from the radio wave being received by the receiving antenna. Alternatively, the second wave-detecting circuit may multiply radio wave voltage shifted by the shifting means from the radio wave being transmitted from the transmitting antenna by radio wave voltage being received by the receiving antenna. Based on output voltages from the first and second detecting circuit, the distance to the target may be decided unambiguously.
A power cutting tool having a movable blade, such as a table saw, comprising a radar sensing system for movement of an object in a region near the blade is disclosed. The radar sensing system emits a radio frequency wave and receives wave energy reflected by the object. The system measures the Doppler shift of the received wave energy to detect the presence of a fast moving object in a zone near the blade. When such a condition is detected, a reaction system can be activated to mitigate the condition.
A primary transceiver of a primary vehicle transmits a first transmission signal to a first transponder and a second transponder associated with a secondary vehicle. A first transponder antenna and a second transponder antenna are associated with secondary vehicular reference points. Upon receipt of the first transmission signal, the first transponder transmits a second transmission signal to a first beacon of the primary vehicle and the primary transceiver. A transmitter antenna and the first beacon antenna are associated with primary vehicle reference points. Upon receipt of the first transmission signal, the second transponder transmits a third transmission signal to the first beacon and the primary transceiver. A data processor or estimator determines propagation times associated with the first transmission signal, the second transmission signal, and the third transmission signal. The data processor or an estimator estimates a relative position of the primary vehicle with respect to the secondary vehicle based on the primary vehicular reference points, the secondary vehicular reference points, and the determined propagation times.
