DEVELOPMENTS IN SHORT-WAVE DIRECTIVE ANTENNAS 683 



by reducing the characteristic impedance of the antenna. One con- 

 venient scheme for reducing the impedance is to employ several con- 

 ductors in parallel in each leg of the antenna. The characteristic im- 

 pedance may in this manner be dropped to a value for which matching 

 iron wire lines are readily constructed. 



The terminating load which produces the most desirable impedance 

 characteristic does not necessarily produce the best front-to-back 

 ratio. In the transmitting case, however, the deep directed nulls re- 

 quired in reception, to eliminate interference of some particular station, 

 are not necessary. It is sufficient to reduce by 10 or more decibels the 

 field in the back directions. Thus the modified diamond-shaped an- 

 tenna may be employed as a unidirectional transmitting array accept- 

 ing power over a two-to-one frequency range. 



In conclusion, I should like to point out that the work described in 

 this paper was possible only through the assistance, cooperation, and 

 advice of many people in the Bell System, to all of whom I render my 

 sincere thanks. In particular, I wish to mention Messrs. A. C. Beck 

 and L. R. Lowry who supervised the construction and did most of the 

 testing of the experimental models. Mr. H. T. Friis, not only con- 

 tributed many suggestions and constructive criticisms of the work, but 

 took steps to have developed apparatus which was essential for the 

 automatic measurement of received signal levels. 



