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BELL SYSTEM TECHNICAL JOURNAL 

 3. Wave Front Analysis 



The fundamental design question is "How to get what we want?" In 

 a radar antenna we want specified radiation characteristics; gain, pattern 

 and polarization. Electromagnetic theory tells us that if all electric and 

 magnetic currents in an antenna are known its radiation characteristics 

 may be derived with the help of Maxwell's Equations. However, the es- 

 sence of electromagnetic theory insofar as it is of use to the radar antenna 



WAVE GENERATOR 



REFLECTING 

 SHEET 



A ^ 



CURRENT 

 SHEET 



WAVE RECEIVER 



REFLECTING 

 SHEET 



RESISTANCE 

 SHEET 



i 2rr ^ 

 MAGNETIC INTENSITY = H = Ie"~?r AMPERES 



METER 

 ELECTRIC INTENSITY= E = 120nH ^OLTS 



METER 



POWER FLOW = P = EH ^^'^ ^^ s 

 METERS 



CURRENT DENSITY^I At^^^^J^^^ 



METER 

 RESISTIVITY =R = 120Tr 0.HM5 



Fig. 7 — Linearly Polarized Plane Electromagnetic Waves. 



designer can usually be expressed in a simpler, more easily visualized and 

 thus more useful form. This simpler method we call wave front analysis. 

 In a transmitting microwave antenna the power to be radiated is used to 

 produce currents in antenna elements which are distributed in space. This 

 distribution is usually over an area, it may be discrete as with a dipole array 

 or it may be continuous as in an electromagnetic horn or paraboloid. These 

 currents generate an advancing electromagnetic wave over the aperture of 



