RADAR ANTENNAS 



235 



factor i e *''^''' ^'^. With this equation as a basis we will now proceed to 

 study some relevant matters concerning radar antennas. 



3.2 Gain and EJJective Area of an Ideal Anlenna 



On the basis of (17) we can now determine the gain of an ideal antenna of 

 area S {S ^ X^). This antenna is assumed to be free of heat loss and to 

 transmit by generating an advancing wave which is uniform in phase and 

 amplitude in the XY plane. Let the electric intensity in the wave front of 



Fig. 9 — An Ideal Antenna. 



the ideal antenna be E^ polarized parallel to the X axis (Fig. 9). The trans- 

 mitted power Pr is equal to the power flow through S and is given by 





(18) 



At a point Q on the Z axis the electric intensity is obtained by adding the 

 effects of all the Huygens sources in S. If the distance of Q from is so 

 great that 



r = d + ^ 



