338 BELL SYSTEM TECHNICAL JOURNAL 



antennas are used in either a lateral array, a longitudinal array, or a 

 combination of the two. 



In the lateral array, the initial ends of the wave-antennas are spaced 

 in the direction perpendicular to the axes of the antennas. Since it 

 extends over space in the lateral direction, unless there be undue sacri- 

 fice in desired signal, the lateral array can only reduce the width of the 

 directional diagram. 



In a true longitudinal array, the antennas are coaxial, but their 

 initial ends are separated by an appreciable fraction of a wave- 

 length. If the wave-antennas forming this type of array overlap one 

 another, then the mutual impedance between them would greatly 

 modify their individual characteristics. In practice, a small amount 

 of lateral spacing between the units of a longitudinal array is necessary 

 to make the mutual impedance negligible. When this type of array 

 is properly designed, the reduction in directional receptivity due to the 

 array is principally in the back-end direction. 



The physical layout of the Houlton antenna system is shown in 

 Fig. 12, and the circuits serving to connect the antennas to the radio 

 receiver are shown in Fig. 11. The same letters are used for corre- 

 sponding line sections in both of these figures. At the time that the 

 directional characteristics of the Houlton antennas were measured, 

 the antenna system comprised only three antennas, A, B, and D. 

 Antenna A at that time extended from pole A-33 to pole A- 117. Two 

 arrays could then be used: antennas B and D forming a lateral array, 

 and antennas A and B forming a modified longitudinal array. In 

 normal operation using either of these two arrays, the transducers in 

 the antenna output circuits were adjusted to combine equal amplitudes 

 of the desired signals from the two antennas in phase with one another. 



Using as the unit antenna for the arrays a directional diagram 

 derived from the average constants of the antennas A, B, and D, 

 the directional diagrams of these two arrays have been computed. 

 Fig. 13 shows the computed directional characteristic of the lateral 

 array and Fig. 14 the computed directional characteristic of the modi- 

 fied longitudinal array. On each of these figures, the measured points 

 are shown. 



The three antennas A, B, and D represented an uneconomical 

 antenna system inasmuch as but two of the antennas could be used 

 simultaneously in an array. To utilize fully these three antennas, at 

 the same time increasing the discrimination against noise, the fourth 

 antenna C has been constructed. To use these four antennas, they 

 are arranged in pairs to form two lateral arrays, and the two lateral 

 arrays arranged in a longitudinal array. The resultant total array 



