Plessey AR-3D
The AR-3D was a military air traffic control and early warning radar developed by Plessey and first produced in 1975. It used a pencil beam and simple frequency scanning system known as "squint scan" to produce a low-cost 3D radar system that was also relatively mobile. About 23 were produced in total and found sales around the world into the early 1980s. The frequency scanning system had the disadvantage that a target aircraft would always be "painted" by the same frequency signal, which made the task of jamming the radar simpler. This limited its sales prospects to military users, and shortly after delivering the AR-3D the company began negotiations with the US company ITT-Gillifan to incorporate their multi-frequency scanning with the AR-3D's receivers and display systems to produce the Plessey AR-320. History Squint During the installation of the first high-power microwave frequency radars using slot antennas, operators of the AMES Type 14 noticed that the apparent angle of the "blips" on the radar display did not always match the physical angle of the antenna. This was traced to an effect in the waveguides, which had slightly different transmission characteristics based on frequency. When the cavity magnetron warmed and cooled during