This paper proposes the antenna arrangement for 2×2 MIMO (Multiple-Input Multiple-Output) sensor and evaluates the detection performance based on raytracing simulation. In this arrangement, the transmitting and receiving antennas are placed closely. Two types of the arrangement are considered. In the first method, all of the transmitting and receiving antennas are located closely. In the second method, two sets of the antennas are placed separately, and each set has one transmitting and one receiving antennas. The numerical analysis of the indoor propagation based on the raytracing method is carried out. The path distribution and intrusion detection performance with the various antenna arrangements are evaluated for the human positions all over the room. The numerical analysis results show that the proposed antenna arrangements achieve the compact configuration of the sensor antenna system as well as high detection performance.