THREE COORDINATE (3D) AIR SEARCH RADARS

General Theory of Operation The AN/GPN-27 is a modular, solid-state, dual-channel, dual-beam/frequency diversity, S-band, surveillance radar used for safe, efficient movement of air traffic within the naval or Marine Corps Air Station National Airspace System area. Some of the operating features include: Stable local oscillator (STALO) MTI with 10-bit design Clutter rejection Circular polarization Reduced side lobes Field-programmable range azimuth gate Configuration The AN/GPN-27 radar includes three major groups: an antenna group, a transmitter building group, and a display site group. The antenna group consists of a reflector, dual-feed assembly, rotary joint, pedestal, and a dual-drive train assembly. It is a dual-beam design with normal and passive channels, including switchable linear and circular polarization. The cosecant-squared elevation pattern provides constant radiation altitude coverage up to 30 degrees above peak of beam. The passive, receiver-only feed horn is tilted upward from the normal beam to reduce interference from ground clutter at short ranges. In the transmitter building group, the transmitter has an air-cooled klystron, a solid-state modularized modulator, and a solid-state, high-voltage power supply. The receiver provides normal video, log video, and moving target indicator (mti) video signals to the processor unit. The digital processor processes the receiver video for the radar tuning and control circuits, the range/azimuth gate generator, the azimuth pulse generator (APG), and the video cable-line drivers. The system control interface and distribution unit features a solid-state control system for radar command and status indications. A 16-inch maintenance plan position indicator (MPPI) aids in system alignment and maintenance. The transmitter building group also has two of the five stations (1 master and 1 slave) of the intercommunication system. The display site group at the indicator site or air traffic control (ATC) room consists of a display site remote unit, two system control panels, a display site cable junction box, and an intercommunications system with three stations (2 master and 1 slave). SIGNIFICANT INTERFACES.— The only interfacing is within the system itself. The control system contains control boxes that have release and take-control circuitry to ensure that radar command is available only at the selected control box. Operators scan the radar screen for incoming and outgoing aircraft, vector aircraft to the airfield, and work with other controllers to coordinate precision approach radars (PAR) and land aircraft. FOR THE MAINTAINER.— The AN/GPN-27 uses state-of-the-art design and technology. All radar command and status signals stay in power-protected solid-state memory, isolating the control system from short-term power outages. The MPPI at the transmitter building aids in system alignment and other maintenance. Maintenance Maintenance of the AN/GPN-27 is performed on demand or as scheduled and is done by Electronics Technicians (NEC ET-1580). Organizational level maintenance includes fault isolation, performance testing, and alignment. Corrective maintenance consists of the removal and replacement of sub-assemblies, modules, and printed circuit boards (PCBs). Those items not repairable at the organizational level are returned to the depot facility through normal Navy supply channels. THREE COORDINATE (3D) AIR SEARCH RADARS Fire Control Technicians (FCs) usually maintain the height-finding radars installed aboard Navy ships. So, rather than cover specific equipment, we will cover general information to help you understand the overall radar capabilities of your ship. The 3D radar functions much like the 2D system, but also provides elevation information. To do this, the height-finding radar uses a beam that is very narrow, both vertically and horizontally. Azimuth is provided as the antenna rotates continuously at speeds varying up to 15 rpm. Although the antenna usually operates in the automatic mode, the operator may 2-14