No. 2, six more in Set No. 3, twelve in Set No. 4, six in Set No. 5 etc. This arrangement is made more clear by reference to Figure 5-13 which shows the first fourteen sets of elements and the number in each set. The average power level in each set is a function of the radius of the circle corresponding to the set. The function is given closely by a gaussian distribution of power density centered at the center of the array. Figure 5-14 shows the correspondence between experimental data and a gaussian distribution for the 199-element array whose performance was verified by the Jet Propulsion Laboratory Quality Assurance Dept, in 1975. It is noted then that the 5-element foreplane structure as shown in Figure 5-13replaces two elements of the No. 1 set, two elements of the No. 3 set, and the single element No. 0 set. Now, if the assumption is made that all individual elements in a set have equal power output the prediction of the power in the foreplane structure in terms of the remaining power in sets No. 1 and 3 may be formulated as : The factor 1.08 in the first term above comes from the fact that the density of power at the center as given by the gaussian distribution is 1. 08 times the power density at the radius of Set No. 1 consisting of 6 elements. All the elements in a set operate in parallel into a common load. The effective load per element is approximately 23.5 ohms. To maintain this effective load, it was necessary to reset the common load values of sets 0, 1, and 3. Figure 5-15 shows experimental data which compare the output of the foreplane structure with the predicted value as given by the preceding formula
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