OCEAN ELECTRONIC NAVIGATIONAL AIDS 



BEARING RESOLUTION 



43 



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TWO TARGETS WITHIN THE BEARING RESOLUTION APPEAR AS A SINGLE PIP. 



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TWO TARGETS SEPARATED BY THE BEARING RESOLUTION ANGLE APPEAR 

 AS TWO TANGENT PIPS. 



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/ mile: 



TWO TARGETS SEPARATED BY MORE THAN THE BEARING RESOLUTION 

 ANGLE APPEAR AS TWO SEPARATE PIPS. 



Figure 4-3. — Bearing resolution. 



While the result of good resolution in range and bearing is a clear, sharply 

 defined PPI picture, giving an accurate contour of land and definite pips for 

 small targets, a Radar of poor resolution would have a blurred and fuzzy 

 appearance with targets blending together on the scope. 



The resolution in range is a function of pulse length, pulse shape, and 

 receiver fidelity. The returning echoes are successively amplified by each 

 of the intermediate-frequency and video circuits of the receiver ; should these 

 circuits modify the returning echoes, poor range resolution will result. The 

 optimum band pass of the receiver should consequently be from 1.2 to 1.5 

 times the reciprocal of the pulse duration in microseconds. As the pulse 

 duration T in microsaconds is equivalent to 164T in yards any targets sepa- 

 rated by less than this value will appear as a single target. 



The resolution in bearing is directly dependent on antenna beam width. 

 For any set frequency, beam width is a function of the antenna dimensions, 

 decreasing as the antenna dimensions increase. Fortunately, as we narrow 

 beam width to improve resolution we increase the over-all gain of the an- 

 tenna system. However, there is a practical limit of about 1° or 2° where 

 further narrowing of the beam causes targets to be missed due to the small 

 number of pulses that will strike it as the antenna scans the target. 



