RADAR ANTENNAS 



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region of the vertical pattern. The elements may be dipoles or waveguide 

 apertures fed directly through the antenna feed line or they may be reflectors 

 which reradiate reflected energy originating from a single primary source. 

 No matter how excited they must be properly controlled in phase, amplitude 

 and directivity. 



Cosecant antennas based on the paraboloid are common and can some- 

 times fulfill all requirements with complete satisfaction. Nevertheless they 



Fig. 34- — Barrel Cosecant Antenna (Cosecant Energy Downward). 



suffer from certain disadvantages. The most serious of these is that they 

 lack resolution at high vertical angles, that is the beam is wider horizontally 

 at high angles. This is to be expected for reasons of phase alone, for a 

 paraboloidal reflector is, after all, designed to focus in only one direction. If 

 phase difliculties were completely absent however, azimuthal resolution at 

 high angles would still be destroyed because of cross polarized components of 

 radiation. These components arise naturally from doubly curved reflectors, 

 even simple paraboloids. They are sometimes overlooked when antennas 

 are measured in a one way circuit with a linearly polarized test field, but 

 must obviously be considered in radar antennas, 



