248 BELL S YSTEM TECH NIC A L JOURNA L 



at his disposal or develop practical methods which can produce the results 

 he requires. The effectiveness and simplicity of these methods are fair 

 measures of the degree of technical development. 



The study of methods of radar antenna construction is the study of the 

 means by which radar antenna requirements are met. In a broader sense 

 this includes an examination of mechanical structures, of the metals and 

 plastics from which antennas are made, of the processes by which they are 

 assembled, and of the finishes by which they are protected from their envi- 

 ronment. It might include a study of practical installation and maintenance 

 procedures. But these matters, which like the rest of Radar have unfolded 

 widely during the war, are beyond the scope of this paper. An adequate 

 discussion of them would have to be based on hundreds of technical reports 

 and instruction manuals and on thousands of manufacturing drawings. The 

 account of methods which is to follow will therefore be restricted to a dis- 

 cussion, usually from the electrical point of view, of the more useful and 

 common radar antenna configurations. 



6. Classification of Methods 



During the history of radar, short as it is, many methods of antenna con- 

 struction have been devised. To understand the details of all of these 

 methods and the diverse applications of each is a task that lies beyond the 

 ability of any single individual. Nevertheless most of the methods fall into 

 one or another of a limited collection of groups or classifications. We can 

 grasp most of what is generally important through a study of these groups. 



In order to provide a basis for classification we will review briefly, from a 

 transmitting standpoint, the action of an antenna. Any antenna is in a 

 sense a transformer between a transmission line and free space. More 

 explicitly, it is a device which accepts energy incident at its terminals, and 

 converts it into an advancing electromagnetic wave with prescribed amph- 

 tude, phase and polarization over an area. In order to do this the antenna 

 must have some kind of energy distributing system, some means of amplitude 

 control and some means of phase control. The distributed energy must be 

 suitably controlled in phase, amplitude and polarization. 



All antennas perform these functions, but different antennas perform 

 them by different means. Through an examination of the means by which 

 they are performed and the differences between them we are enabled to 

 classify methods of antenna construction. 



To distribute energy over its aperture an antenna can use a branching 

 system of transmission lines. When this is done the antenna is an array. 

 Arrays are particularly common in the short wave communication bands, 

 but somewhat less common in the microwave radar bands. In a somewhat 

 simpler method the antenna distributes energy over an area by radiating it 



