PURPOSE: To detect the direction of radio wave arrival without analyzing the frequency nor being affected by variation in antenna characteristics by recording and comparing received pulse waveforms.

CONSTITUTION: Antennas 3a and 3b are arranged at points A and B and when the pulse input of an arrival radio wave is received at the point A, it is recorded and the time (t) up to the input point of a pulse with a similar waveform to the point B is measured. This time (t) is calculated from t=d.cos (where d is the distance between the antennas and is the angle of the arrival wave to the axis connecting the points A and B), so when the distance (d) is accurately grasped, reverse calculation is carried out to obtain the radio wave arrival direction . Waveforms are compared by calculating the similarity of the whole. In this case, similarity is calculated as to the amplified in the form of not an absolute value, but a relative value, so the influence of variation of the characteristics of the antenna is eliminated. A frequency analysis is not necessary and antenna characteristics and connection line characteristics are not limited.