A MULTIPLE UNIT STEERABLE ANTENNA 



401 



the reduction of noise obtained with 60-degree phase difference with 

 the addition of 100 or 150 microseconds delay. The 0.8- or 0.9-decibel 

 correction for the two-bundle case corresponds to any large delay and 

 a large phase difference, say 160 degrees. These corrections would not 

 have been much different if a weighting network had been used. 



The measured difference of 1.5 decibels, shown in Table III, between 

 the one-wave bundle and the two-wave bundle measurements is 

 probably real and due to the fact that when the branches are steered at 

 two separated bundles some loss is incurred when one wave disappears 

 for a few minutes. This loss could have been at least partly recovered 

 by using square-law detectors. Tests showing the advantage of 

 square-law detectors over linear detectors are described later in this 

 section. Employing square-law detectors would justify a correction of 

 about one decibel to be added to the two-bundle improvement measure- 

 ments in Tables III and IV. Applying this correction we summarize 

 the results in Table V. 



TABLE V 



Summary of Signal-to-Noise Measurements 



These improvement figures for two branches as they stand are 

 approximately equal to 10 log 6 = 7.8 decibels as calculated for non- 

 fading waves, and leave nothing to be ascribed to diversity action. 

 Since a loss of perhaps one decibel occurs in the case of one branch 

 (Table II), the recovery of that one decibel with two branches is to be 

 ascribed to diversity action. Originally, considerably more was ex- 

 pected of the angle diversity. It appears however from theoretical 

 and experimental evidence that one decibel is about what should be 

 expected for the case in hand. It seems appropriate to include this 

 study of diversity here. 



Diversity Action 

 The first attempt to analyze diversity action was made with a 

 graphical approach to the problem. On Fig. 38 is shown a schematic 

 diagram of the system to be analyzed. Two receivers A and B with 

 linear audio detectors may be regarded as fed from two angle branches 

 of a MUSA. The noise generators Bua and enB are assumed to be of 



