HORIZONTAL RHOMBIC ANTENNAS 



149 



in this manner is shown in Fig. 13. In this figure is also shown, for 

 comparison purposes, the pattern calculated for these conditions by the 

 equations derived in the appendix. The agreement between these two 

 patterns is quite evident. 



CALCULATED 





MEASURED 



50 Z 

 < 



Fig. 13 — Receiver current diagrams of test antenna output current versus azimuth 

 angle for a 2.7° wave-angle. 



To check the vertical directivity of the system, a portable oscillator 

 was raised from the ground to the top of a one-hundred foot pole in 

 front of the antenna. Due to the limited range of arrival angles so 

 obtained, only the major lobe of the directive pattern could be traced 

 out. Figure 14 gives the calculated major lobe for these conditions 

 (equations corrected to actual path length difference between direct and 

 reflected waves) with the antenna one-half wave-length above ground, 

 and Fig. 15 is the pattern at a height of one wave-length. The circles 

 on these curves are the measured values. These patterns show that 

 the directivity does not change very rapidly with changes in antenna 

 height. 



Experimental checks of these directivity calculations have also been 

 obtained on the larger antennas ordinarily used for long distance 

 reception. A large horizontal rhombic antenna was constructed with a 



