HORIZONTAL RHOMBIC ANTENNAS 



139 



Using the perfect ground assumption, the ampHtude of equation (1) 

 is given by 



Ir = k' 



sin I -^ — sin A 



[cos (f) 1 



1 — sin (p- cos A J 



(1 — sin 0- cos A) 



}. (2) 



<d 



a ISO 



175 



10 20 30 40 50 60 70 80 90 100 



INCIDENT WAVE-ANGLE IN DEGREES (A°) 



Fig. 2 — Characteristics of \va\e-reflections from ground. 



In this equation the first bracketed term may be referred to as the 

 "height" factor, the second as the "asymmetrical directivity" factor, 

 and the third as the "phasing" factor. 



Maximum Output Design Method 

 In maximizing equation (2), it is necessary to deal with three 

 variables, the antenna dimensions //, I and </>. Differentiating with 

 respect to each of these variables, while holding the other two constant, 

 and equating to zero, the following three expressions are obtained: 



8In 

 8H 



= when 



11 = 



4 sin A 



for the lowest practical height, 



