Page:Electronics Technician - Volume 7 - Antennas and Wave Propagation - NAVEDTRA 14092.pdf/50

 RADAR SYSTEMS

Now that you have a basic understanding of how radar antennas operate, we will introduce you to a few of the radar systems currently in use.

AN/GPN-27(ASR-8) AIR SURVEILLANCE RADAR

The AN/GPN-27(ASR—8) (fig. 2-47) antenna radiates a beam 1.5 degrees in azimuth and shaped in elevation to produce coverage of up to approximately 32 degrees above the horizon. This provides a maplike presentation of aircraft within 55 nautical miles of an airport terminal. The antenna azimuth pulse generator (APG), located in the rotary joint, transmits to the radar indicator azimuth information corresponding to beam direction. Polarization of the radiated energy can be remotely switched to either linear or circular polarization. The reﬂector has a modified parabolic shape designed to produce an approximately cosecant squared beam in the elevation plane. The reflector surface, covered with expanded aluminum screen, is 16.1 feet wide and 9 feet high. The antenna feedhorn, which mounts on the polarizer, provides impedance matching between the waveguide system and free space, and produces the desired feed pattern to illuminate the reflector. A radome over the horn aperture excludes moisture and foreign matter, and provides a pressure seal.

AS-3263/SPS-49(V)

The AS—3263/SPS-49(V) antenna (fig. 2-48) consists of three major sections: the antenna base and

Figure 2-47.—AN/GPN-27(ASR-8) air surveillance radar. 2-28