Precision Approach Monitoring and Guidance using Interferometer Techniques

The PAIR (Precision Approach Interferometer Radar) system accurately measures the position of aircraft in the airfield approach sector. A ground-based interrogator transmits a conventional SSR code. Aircraft transponder replies are received by an azimuth and elevation interferometer and the angular position measured to high accuracy. Range is measured from the go-and-return time. Aircraft identity is obtained from the SSR IDENT code. Ground reflections are reduced by means of a null in the vertical pattern of the elevation interferometer. Fruit and garbling effects are removed in the signal processing. The aircraft positional information is processed in a mini-computer and presented to the operator on a bright graphical display, and automatic conflict detection can be provided. Applications of the system are ATC terminal area control, MLS and ILS monitoring and ground controlled approach.