This article presents a direction-finding method based on phase difference measurement that is applied in electronic intelligence. Including three processing steps of rotating, re-scaling, and rounding of phase plane or phase space, the proposed method is able to obtain the actual phase shift of the longest baseline from the ambiguous phase differences measured from incoming signals with low computational complexity. The performance of method is analyzed and evaluated in terms of angle of arrival (AOA) estimation accuracy and probability of unambiguity by two interferometers of long baselines, which are designed by three and four antenna elements, respectively. Then, an optimized array configuration of four antenna elements is taken into account for obtaining a high AOA estimation accuracy via several productive simulations and further validated with a practical measurement. Regarding the simulation of angle estimation accuracy and resolution, the proposed method remarkably outperforms two other existing methods, including second-order difference array and correlative interferometer. With respect to the experimental measurement, a high AOA determination accuracy is achieved with the transmitter located about 33.5 meters far from an antenna array. In particular, we obtain the mean angle estimation error of 1.86 degrees for the transmitter's direction at 20 degrees. For various directions from -60 to $60 degrees with the steps of 5 degrees, the results satisfy the actual directions of transmitter with a standard deviation of less than 0.5 degrees.