RADIATION CHARACTERISTICS OF AN ANTENNA. 



211 



PART 11. 



Field due to horizontal Portion of Antenna. 



12. Introductory Notions. — To determine the electromag- 

 netic field and radiation characteristics of the horizontal flat-top 

 portion of the antenna, let the rectangular coordinates of any distant 

 point P (Fig. 7) be x, y, z. 



Figure 7. 



And let the coordinates of any point P' on the flat-top be x', 0, a; 

 the coordinates of the image point P" be x', 0, — a. 



Then the distance from the origin of coordinates to the distant 

 point is 



OP = ro = Vx2 + i/ + z^ 



The distances of the distant point from the point on the flat-top 

 and its image respectively are 



P' P = r' = ^{x - x'y + y^-\- [z- ay 



and 



P" p = r" = V(.r - .t')^ + y- + (z+ ay-. 



Then r - r, = <{x - xj + y' + {z - a)^ - Vx-^ + y^ -\- 



