A Multiple Unit Steerable Antenna for Short- Wave 

 Reception * 



By H. T. FRIIS and C. B. FELDMAN 



This paper discusses a recei\ing system employing sharp vertical- 

 plane directivity, capable of being steered to meet the varying 

 angles at which short radio waves arrive at a receiving location. 

 The system is the culmination of some four years effort to determine 

 the degree to which receiving antenna directivity may be carried 

 to increase the reliability of short-wave transatlantic telephone 

 circuits. The system consists of an end-on array of antennas, of 

 fixed directivity, whose outputs are combined in phase for the 

 desired angle. The antenna outputs are conducted over coaxial 

 transmission lines to the receiving building where the phasing is 

 accomplished by means of rotatable phase shifters operating at 

 intermediate frequency. These phase shifters, one for each an- 

 tenna, are geared together, and the favored direction in the vertical 

 plane may be steered by rotating jthe assembly. Several sets of 

 these phase shifters are paralleled, each set constituting a separately 

 steerable branch. One of these branches serves as an exploring or 

 monitoring circuit for determining the angles at which waves are 

 arriving. The remaining branches may then be set to receive at 

 these angles. The several receiving branches have common auto- 

 matic gain control and thus provide a diversity on an angle basis. 

 To obtain the full benefit of the angular resolution afforded by the 

 sharp directivity, the different transmission times, corresponding 

 to the different angles, are equalized by audio delay networks, 

 before combining in the final output. 



The experimental system, located at the Bell Telephone Labora- 

 tories' field laboratory near Holmdel, New Jersey, is described. 

 This system comprises six rhombic antennas extending three 

 quarters of a mile along the direction to England. Two recei\-ing 

 branches, in addition to a monitoring branch, are provided. Ex- 

 perience obtained with this system since the spring of 1935 is 

 discussed. The benefits ascribable to it are (Da signal-to-noise im- 

 provement of seven to eight decibels, referred to one of the six 

 antennas alone, and (2) a substantial quality improvement due 

 jointly to the diversity action and the reduction of selective fading. 



While a three-quarter-mile short-wave antenna system is an 

 unusually long one, the steerability feature permits the employment 

 of considerably more directivity, afforded by further increasing the 

 length. A system two miles long is believed to be practicable and 

 desirable. It could be expected to perform more consistently 

 better than the three-quarter-mile trial installation, and should 

 yield a signal-to-noise improvement of twelve to thirteen decibels 



* Presented before Silver Anniversary Convention of the Institute of Radio 

 Engineers, New York City, May 10, 1937. Published in Proc. I. R. E., July, 1937. 



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