The radar-based advanced driver assistance systems (ADAS) like autonomous emergency braking (AEB) and forward collision warning (FCW) can reduce accidents, so as to make vehicles, drivers and pedestrians safer. For active safety, automotive millimeter-wave radar is an indispensable role in the automotive environmental sensing system since it can work effectively regardless of the bad weather while the camera fails. One crucial task of the automotive radar is to detect and distinguish some objects close to each other precisely with the increasingly complex of the road condition. Nowadays almost all the automotive radar products work in bidimensional area where just the range and azimuth can be measured. However, sometimes in their field of view it is not easy for them to differentiate some objects, like the car, the manhole covers and the guide board, when they align with each other in vertical direction. In other words, those objects are counted as one erroneously because of absence of height information. In practice, road conditions are complicated and unpredictable, these unexpected mistakes will make the ADAS poor performance or even collapse, e.g. unwanted abrupt brake due to the detected manhole cover or guide board. Plus, the subsequent target tracking would be made an arduous task and with untrusted output. This paper proposes an automotive radar architecture with two-dimensional electronic scanning, which can obtain 3D information--range, azimuth and height. Four antennas including one transmitting antenna and three receiving antennas are used in this scheme. In addition to two conventional receiving antennas placed in horizon, another receiving antenna is arranged in vertical aligning with one of the other two to obtain the height information so that the corresponding detected targets can be distinguished clearly. Furthermore, when more antennas utilized this architecture can be extended easily for higher autonomous driving requirements. A range of simulation indicates that this radar architecture can measure object height and the effectiveness of proposed architecture is further verified in actual experiments on the corresponding radar prototype. It is low-cost and with small size, and the car grade design and development make the further application in ADAS possible.