RADIATION CHARACTERISTICS OF AN ANTENNA. 



197 



PART I. 



Field due to vertical portion of Antenna. 



5. Coordinates. — Let the origin of coordinates be at the point 

 of connection of the antenna to the ground. Let the z-axis be vertical. 

 About this vertical axis as polar diameter, let us construct a system 



Figure 3. 



of polar coordinates in which the position of any point P is given by 

 its distance Tq from the origin, and the angles 6 and 0. 



9 = the angle along meridional lines from the pole, 

 (/) = the angle along parallels of latitude from a vertical plane of 

 reference whose position is at present immaterial. 



This system of coordinates with the positive directions of the angles 

 indicated is given in Figure 3. 



If z' is the vertical ordinate of any point P' on the vertical portion 

 of the antenna, and r the distance from P' to P, and if the distance OP 

 is large in comparison with z', we may write (see Figure 4) 



r = To — z'cos 6. 



(9) 



