A radar system is described, which includes a built-in calibration/fault detection apparatus that enables rapid and easy calibration of the system. The system includes a long extrusion (70) forming a feed waveguide (90), a calibration waveguide (92), and a base (94) of a horn antenna. A linear array of TR (transmit/receive) units (42) are mounted on the extrusion, with each having a feed probe (100) that receives a feed signal, changes its phase and amplifies it, and delivers it through a monopole (110) to the horn. The calibration waveguide is coupled through holes (130) to the horn, with a calibration pickup (132) mounted at the end of the calibration waveguide. During calibration, one TR unit at a time is energized, and its output is detected by the calibration pickup to check the amplitude and phase of the TR unit.