RADAR ANTENNAS 247 



4. Application of General Principles 



In the foregoing sections we have provided some discussion of what hap- 

 pens to a radar signal from the time that the pulse enters the antenna on 

 transmission until the time that the reflected signal leaves the* antenna on 

 reception. We have for convenience divided the principles which chiefly 

 concern us into three groups, transmission line theory, transmission prin- 

 ciples and wave front theory. 



With the aid of transmission line theory we can examine problems con- 

 cerning locally guided or controlled energy. The details of the problems of 

 antenna construction, such as those to be discussed in Part II frequently 

 demand a grasp of transmission line theory. With it we can study local 

 losses, due to resistance or leakage, which affect the gain of the antenna. 

 We can examine reflection problems and their effect on the match of the 

 antenna. Special antennas, such as those employing phase shifters or trans- 

 mission between parallel conducting plates, introduce many special prob- 

 lems which lie wholly or partly in the transmission line field. 



An understanding of the principles which govern transmission through 

 free space aids us in comprehending the radar antenna field as a whole. 

 Through a general understanding of antenna gains and effective areas we 

 are better equipped to judge their significance in particular cases, and to 

 evaluate and control the effects of particular methods of construction on 

 them. 



Wave front theory provides us with a powerful method of analysis through 

 which w^e can connect the radiation characteristics produced by a given 

 antenna with the radiating currents in the antenna. Through it we can 

 examine theoretical questions concerning beam widths and shape, unwanted 

 radiation and gain. 



An understanding of theory is necessary to the radar antenna designer, 

 but it is by no means sufficient. It is easy to attach too much importance 

 to theoretical examination and speculation while neglecting physical facts 

 which can 'make or break' an antenna design. Theory alone provides no 

 substitute for the practical 'know- how' of antenna construction. It cannot 

 do away with the necessity for careful experiment and measurement. Least 

 of all can it replace the inventiveness and aggressive originality through 

 which new problems are solved and new techniques are developed. 



PART II 



METHODS OF ANTENNA CONSTRUCTION 



5. General 



Techniques are essential to technical accomplishment. An understanding 

 of general principles alone is not enough. The designing engineer must have 



