4 ELEMENTS OF AIRBORNE RADAR SYSTEMS DESIGN PROBLEM 



definition can serve as the basis for arbitrating conflicting design require- 

 ments resulting from the multimode requirement. 



The specific functions performed by a radar system are outlined below 

 in somewhat more detail. 



Search and Detection. An important function of a radar system is 

 to interrogate a given volume of space for the presence (or absence) of a 

 target of tactical interest. One very common method by which a radar 

 system may be used to perform this function is shown in Fig. 1-1. In this 



,-»- Search Radar 



Scan Pattern 



ar Search and Detection. 



example, RF (radio-frequency) energy is generated in the radar system 

 (active system). This energy is focused into a highly directional beam by 

 an antenna and propagated through space. Should there be an object of 

 appropriate characteristics within the radar beam, a portion of the electro- 

 magnetic energy impinging on the object will be scattered away from it. 

 A portion of this scattered energy finds its way back to the point of trans- 

 mission where it may be detected by a receiver. 



In order to extend the space coverage of the radar system, it is customary 

 to scan a predetermined volume of space in a cyclic manner by changing 

 the direction of propagation as indicated in Fig. 1-1. 



Identification. The system may be required to operate in an area 

 where both friendly and unfriendly aircraft or targets possibly exist. 

 A requirement will then arise to search the area and identify any targets 

 as friend or foe (IFF). When it is performing the search and detection 

 function, the radar system generates answers to a specific question: Is 

 there — or is there not — a target of tactical interest within a given volume 

 of space? The basic characteristics of a radar — or any detection device 

 ■ — are such that both correct and incorrect answers to this question may 

 be generated. There are, in fact, four possible sets of circumstances: 



1. There is a target within the searched volume and its presence is 

 detected by the radar. 



