Abstract: An improved direction finding apparatus for determining the azimuth of a target source of radio frequency signals using in an optimal manner the signals from a central antenna and an associated array of direction finding antennas. The signals of the antennas are repeatedly scanned to generate running averages of the inphase and quadrature phase components of the RF phasors and to thereby reduce the effect of system noise on the measurement of the phasors. A series of computed candidate phasors corresponding to candidate target sources are then compared to the measured phasors and the azimuth of the candidate target having phasors most closely approximating the measured phasors is an optimal determination of the unknown azimuth of the actual target.