Abstarct: Abstract Finding the location of electromagnetic, acoustic and vibration wave sources by passive array systems have many applications in positioning systems, defense issues, geo-physics, and particularly recently in the industry. There are several techniques for locating passive radar, such as RSS, AOA, and TDOA. The TDOA technique in terms of accuracy and simplicity is better than the others. There are several algorithms to obtain the location of target baxsed on TDOA method. Some of these are: 1- Hyperbolic or Elliptic Line of Position (LOP) method. 2- Location on the Conic Axis (LOCA) method. 3- Spherical Interpolation (SI) method. 4- Spherical Intersection (SX) method. Some of these methods are expressed for two situation in detail. First, when the target is the emitter. Second, when the target is reflecting object. Error analysis is a measure of the accuracy of these methods. Error analysis of SI method is expressed and then its value have been obtained with higher accuracy. Via simulation, the most appropriate placement is selected among several possible sensor placements in a circular coverage area and in the case of a minimal number of sensors.