RADAR - Beamwidth at a certain Range
Equation: 

 Rc(km)    =  ( ( beamwidth (deg.) x range (km))  /  60))
 Rc    =    resolution cell
 
Example:

Rc    = (1.4 x 100) / 60    = 2.3 km  beamwidth at 100 km range
 (1 km  = 0.62 mi)