3-6] 



FACTORS AFFECTING ANGULAR RESOLUTION 



, Average 

 ^Out of Phase 

 ,ln Phase 



171 



-50/2 -29 -39/2 -9 -Q/2 9/2 9 39/2 29 5Q/2 



Fig. 3-16 Two-Way Voltage Envelope Generated by a Scan over Two Targets 

 Separated by One Beamwidth. 



in phase, only a small notch separates the two targets — they have merged 

 in a single return. When the received signals are out of phase, there is a 

 sharp null midway between the two targets. An average envelope can be 

 determined for a random phase between the two reflections. This average 

 two-way voltage envelope is also shown in Fig. 3-16. The minimum of this 

 average curve is 0.707 of the maxima corresponding to half of the maximum 

 received power. Consequently, the case illustrated in Fig. 3-16 shows the 

 envelope of two targets which are just barely resolved. These targets are 

 separated by a single beamwidth. Thus the definition of resolution adopted 

 conveniently yields one beamwidth for two targets of equal size. 



Degrading Influences. In most practical situations the resolution 

 will be degraded somewhat by a variety of factors. One such factor is 

 unequal strength of the targets. In Fig. 3-17, the two-way voltage envelope 



Target 1 



Target 2 



-39/2 -9 



Fig. 3-17 Average Two-Way Voltage Envelope Generated by a Scan over Two 

 Separated Targets of Unequal Size (4 : 1 Power Ratio). 



is shown of two targets whose maximum received voltages have a 2-to-l 

 ratio. The radar size of these two targets is normally expressed in terms of 



