appear as one echo. In short, multiple targets at a distance are difficult to see correctly. Sidelobes In  addition  to  the  main  beam,  antennas  produce rays  of  energy  called  sidelobes,  which  surround  the main beam (primary lobe) like haloes (fig. 2-12). Sidelobes extend outward only a short distance from the  radar  and  contain  very  low  power  densities. However, even though they are weak, sidelobes can detect strong non-meteorological targets near the radar and are also disturbed by nearby g-round reflections. This leads to confusion in interpreting close targets because sidelobe targets are displayed along with the main  beam  targets. RADAR  RESOLUTION Radar  resolution  is  the  radar’s  ability  to  display targets correctly. Both azimuthal resolution and range resolution  are  problems  that  commonly  effect  all radars.  Recall  our  earlier  discussion  about  distant objects and their distorted appearance. Resolution affects radar much the same way. Azimuthal Resolution Azimuthal resolution is often called bearing or directional resolution. It is a radar’s ability to display side-by-side  targets  correctly.  Azimuthal  resolution  is controlled by beam width as only targets separated by more than one beamwidth can be displayed separately. As the radar antenna rotates, targets too close together occupy the beam simultaneously. This causes them to be displayed as one wide target, stretched azimuthally (sideways). Since azimuthal resolution depends on beamwidth, which changes with distance, targets  near  the  antenna  require  less  separation  than those further out. Near the antenna, a narrower beam allows the radar to recognize tighter gaps and display targets   separately.   At   greater   distances,   more separation is required. If targets are not separated by the   prescribed   amount,   distortion   occurs   and resolution  suffers.  With  the  WSR-88D,  azimuth distortion is approximately 1 mile at a 50-nmi range. Thus, at 250 nmi, two targets must be about 5 miles apart before they will appear as two separate targets. Figure 2-12.—Radar sidelobes. 2-9


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