A sensor includes a reception antenna, a parasitic antenna terminating in a variable load, a controller, a transmitter transmitting a transmission signal, a receiver, a memory, and a processor. The controller sets an impedance value of the variable load. The receiver receives a first signal formed of signals received by the antennas and derived from the transmission signal, and the signal received by the parasitic antenna corresponding to the impedance value. The memory stores a first signal strength value of the first signal corresponding to the impedance value. The processor sets candidates of a complex propagation channel, calculates second signal strength values of a second signal respectively corresponding to the candidates, estimates a target complex propagation channel by selecting a candidate corresponding to a minimum difference among differences between the first signal strength value and the second signal strength values, and estimates a direction of arrival of the first signal.