A vehicle traffic sensor for detecting and monitoring vehicular targets is presented. The sensor employs a planar design resulting in a reduced profile sensor. The sensor includes a multi-layer radio frequency board with RF components on one of the sides and both isolation and planar array antennas on the opposing side. The antennas are preferably tapered planar array antennas which include one transmit antenna and one receive antenna. The sensor also includes at least one logic or signal processing board populated with components on a first side and a ground plane on a second side positioned toward the RF componentry of the RF board to form an RF shield. The boards are housed within a housing that is permeable, at least on the side through which the antenna structures propagate.