340 BELL SYSTEM TECHNICAL JOURNAL 



in general suitable for quality improvement. For such studies it would 

 be preferable to construct a more elaborate antenna whose directional 

 pattern has a single major lobe which is steerable in the vertical plane. 

 Such an antenna would aim to select a narrow range of angles in which 

 occur waves of substantially the same delay." 



The present paper describes a steerable antenna receiving system of 

 the general character suggested by the above quotation, and which 

 has been in experimental operation at the Holmdel, New Jersey, field 

 laboratory of the Bell Telephone Laboratories for the past two years. 

 Certain other important features are incorporated in the system, 

 notably an arrangement whereby individual wave groups arriving at 

 different vertical angles are received separately and, after separate 

 delay equalization, combined, thereby incorporating a unique form of 

 diversity. Another important feature possessed by the system is its 

 frequency range which permits operation on all of the frequencies used 

 in short-wave transatlantic services. 



II. Principles of Steering Antenna Directivity 



An old and elemental type of steering of receiving antenna direc- 

 tivity is found in direction finders. The steering of a directional lobe 

 as distinguished from the steering of a null has been accomplished in 

 recent years. .Schelleng •* reported a moderate degree of horizontal 

 plane steering, accomplished by means of phase shifters. Jansky ^ 

 has obtained horizontal steering by bodily rotating an entire broadside 

 array. Bruce and Beck ^ obtained vertical steering by varying the 

 shape of a rhombic antenna by means of ropes, and demonstrated the 

 value of steering in the reduction of selective fading. The present 

 authors ^ have employed rotatable phase shifters to steer the nulls in 

 the directional patterns of two spaced antennas. In that work the 

 value of the rapid adjustments possible with phase shifters was very 

 apparent. In the linear end-on MUSA ^ system to be described 

 rotatable phase shifters are again employed to steer the vertical 

 response.^ 



In Fig. 1 is shown a schematic representation of a linear end-on 

 array of N equally spaced unit antennas in free space. The antennas 

 are indicated by the numbered points. For simplicity it is assumed, in 

 the following preliminary analysis, that the antennas are spaced far 



"J. C. Schelleng, "Some Problems in Short-Wave Telephone Transmission," 

 Proc. L R. E., vol. 18, pp. 913-938, June, 1930. 



^ K. G. Janskv, "Directional Studies of Atmospherics at High Frequencies," 

 Proc. L R. E., vol. 20, pp. 1920-1932, December, 1932. 



*The word MUSA is coined from the initial letters of "multiple unit steerable 

 antenna." 



nj. S. Patent No. 2,041,600. 



