234 



BELL SYSTEM TECHNICAL JOURNAL 



Here 



Ef^dS 



is an amplilude factor which depends on the wavelength, intensity 



and area of the elementar}' source and \/r is an amplitude factor which 

 specilies the \ariation of field with distance. (1 + cos 6) is an amjilitude 

 factor which shows that the directional pattern of the elementary source is a 

 cardioid with maximum radiation in the direction of propagation and no 

 radiation in the reverse direction. 



When we use the properties of the Huygens source in analyzing a micro- 



Fig. 8 — The Huygens Source. 



wave antenna we are usually concerned principally with radiation in or near 

 the direction of propagation. For such radiation Equation 16 takes a par- 

 ticularly simple form in Cartesian Coordinates 



E, 



.£^^_,(,WX)r.^^^Q.^^^Q_ 



(17) 



This represents an electric vector nearly parallel to the electric vector of the 

 source. The amplitude is given by the factor ^ and the phase by the 



