GAIN OF DIRECTIVE ANTENNAS 77 



Two cases are of special interest. First, it is sometimes desirable to 

 divide an array into two or more bays, in order to make room for a 

 supporting structure. This, of course, gives rise to a definite discon- 

 tinuity in the over-all array. 



Fig. 13 shows a series of diagrams resulting from a typical case 

 of two such arrays, each having a length of 2>^ wave-lengths but 

 separated variously from to 2 wave-lengths in steps as noted. These 

 diagrams, of course, do not take into consideration the reaction re- 

 sulting from proximity to an antenna mast, located in such an opening. 

 The most important result is to emphasize the spurious lobes, as the 

 spacing between arrays is increased. 



A second effect of grouping which is of considerable interest is that 

 of varying the direction of transmission by altering the respective 

 phases betw^een two or more arrays or between sections of the same 

 array. In Fig. 14 a series of diagrams Is shown for a typical case of 

 two 3J4 wave-length arrays, spaced one wave-length. All elements in 

 the same array are driven in phase, but the two arrays differ in phase 

 by various amounts, as noted. It will be observed that the possible 

 rotational effect is very limited. The general equation for this diagram 

 is given by formula (36) of the mathematical appendix. 



This effect was investigated further by assuming a continuous array 

 7}^ wave-lengths long, made up of 16 couplets spaced at intervals 

 of ^ wave-length. The results are depicted in Fig. 15. The top row 

 assumes that the array is divided into two sections of eight couplets 

 each. This gives similar but not exactly the same results as those of 

 Fig. 14. The array, however, might have been divided into other sec- 

 tions for purposes of phasing. The various possible combinations are 

 tabulated below: 



Number of Number of Couplets 



Sections per Section 



2 8 



4 4 



8 2 



16 1 



Diagrams in rows two, three, and four show that, as the array 

 continues to be divided into smaller sections, the direction of trans- 

 mission is capable of greater variation without sensible loss of sharp- 

 ness. If the array be divided into two sections this range is limited 

 to perhaps 3 deg. as in the case depicted in Fig. 14. Although this is 

 very moderate, it is extremely useful in correcting for any errors in 

 the orientation of the supporting structure or possibly correcting for 

 deviation of the projected radiation caused by peculiarities of the ad- 

 jacent terrain. 



