136 BELL SYSTEM TECHNICAL JOURNAL 



received. Such information has been obtained by employing the 

 methods described by Friis, Feldman and Sharpless.- 



In general, the principal axis of the antenna departs very little from 

 the true bearing of the station to be received. However, the average 

 vertical direction of the waves in the incident plane and their angular 

 variation have an effect upon the determination of the correct dimen- 

 sions of a horizontal rhombic receiving antenna. 



Without careful consideration, one might be led to believe that the 

 theoretical effectiveness of a horizontal rhombic receiving antenna 

 would increase without limit, for a stable wave-direction, as the 

 properly related dimensions are increased. It will be shown that, for a 

 given incident wave-angle above the horizontal, the optimum di- 

 mensions have quite definite values. 



The essential dimensions of this type of antenna are its height above 

 ground, the length of a side element, and the inclination angle of these 

 elements in respect to the wave-direction. At frequencies higher than 

 about fifteen megacycles, this type of antenna is relatively so inex- 

 pensive that it is usually economically possible to select a combination 

 of these dimensions which will produce the maximum signal output. 



At lower frequencies, the increasing cost, particularly of the pole 

 height required for maximum output, demands that a careful analysis 

 be made of effective compromise designs. One such design method 

 involves a sacrifice in antenna height, which sacrifice can be partially 

 compensated for by an increase in element length. Thus the economic 

 balance involves a weighing of supporting structure costs against the 

 cost of land. Again, cases may arise where the recommended antenna 

 height is practical but a sacrifice in element length is essential. The 

 effect of this sacrifice on the directive pattern can be partially compen- 

 sated for by a readjustment of the tilt-angle of the elements. The 

 directive pattern may also be aligned with the wave-angle when both 

 height and element length are reduced, but only at an output sacrifice. 



The designer's first problem is to choose between the maximum 

 output arrangement and the various compromise designs. In the case 

 of a transmitting antenna, the problem is to create as large a field as 

 possible at the distant receiving point, for a given amount of trans- 

 mitter power. As long as the increase in antenna cost is smaller than 

 the corresponding cost of an increase in transmitter power, no compro- 

 mise should be made in the antenna dimensions. It is, therefore, 

 obvious that the choice, between optimum and compromise dimensions 

 for a transmitting antenna, is a function of the cost of the transmitter 

 to be employed. 



2 "The Determination of the Direction of Arrival of .Sliorl Radio Waves," by 

 H. T. Friis, C. B. Feldman and W. M. Sharpless, Proc. L R. E., January, 1934. 



