A radar system with antenna modules that have first and second planar slotted waveguide antenna arrays for radiating and receiving electromagnetic waves. A rotation system supports and rotates the antenna modules around a vertical axis. The modules are arranged back-to-back on opposite sides of a plane intersecting the vertical axis of rotation. Another radar system includes planar slotted waveguide antenna arrays with longitudinal extending waveguide columns. The front side of the columns holding the cavity slots of the first planar antenna array are positioned in a first plane and the front side of the columns holding the cavity slots of the second planar antenna array are positioned in a second plane parallel to the first plane. The arrays may be positioned at a distance to each other in a direction to the first and second planes. The parallel planes may be offset with a minimum perpendicular array distance.