In the last decade, radar-based Advanced Driver Assistance Systems(ADAS) have improved transportation safety. And today, the standardization of ADAS by NCAP is expected to expand its market globally. One of the key technology for ADAS is rear-side monitoring system enabling application such as Blind Spot Warning(BSW) and Lane Change Warning(LCW). It is desired to expand the detection range so that it can monitor not only nearside targets widely for BSW but farther targets for LCW. These applications can be achieved by using two radar sensors installed at rear-side corner of the vehicle. However, wider and farther detection range causes the undesirable target detection and decreases target recognition performance. In this paper, a novel solution to improve the performance by using 2FCW-based Beamspace technology is introduced. Combined with IQ detector, 2FCW receiver outputs beat signal proportional to the relative speed of an object. IQ detector is hardware architecture to distinguish approaching and leaving object by separating carrier upper and lower frequency by measuring the relative phase of signal components. This method can achieve good reduction performance of undesirable targets for BSW but not enough for LCW, because LCW focusing area is different from BSW. To design the focusing area for multi-application, control of receiving-directivity is important. The key technology of this paper, Beamspace signal processing, narrows down the objects which exist behind the self vehicle by steering software receiving-directivity backwards, so that it can detect only desirable targets in LCW focusing area. From our experimental result in real environment, LCW alarm rate has reached up to 99%.