show clearly in the form of concentric circles the relatively small amount of reflected power associated with relatively large variations in admittance from that which matches the generator source. It is noted that a very wide range of input power is associated with a value of reflected power less than 1% of the incident power. The data in Figure 5-11 are plotted in admittance form. The conductance component tends to remain constant, while the susceptance component varies with the input power level. A variation in the DC load resistance tends to vary both the conductance and susceptance components. The variation in susceptance as a function of power level undoubtedly comes from the variation in the capacitance of the Schottky barrier diode as a function of the bias voltage which is determined by the power level and the value of DC load resistance. The average value of this capacitance gets reflected back through the two-stage low loss filter to the point at which the admittance is being measured. 5. 7 Test of the 5-element Foreplane as an Integrated Part of a Larger Array The 5-element foreplane structure was integrated into the 199- element rectenna array and an attempt was made to uncover important differences between the behavior of the rectenna prior to such incorporation. No important differences were discovered. The foreplane assembly consisting of the metallic shield and the core assembly of five rectenna elements was mounted in the central portion of the 199-element rectenna, as shown in Figure 5-12. The output power from the foreplane, as experimentally measured, was then compared with what the power output would have been from the five individual elements that it replaced, according to a formula to be explained later. On the basis of this comparison, the measured power output of the foreplane structure was found to be slightly higher than predicted at lower power and about the same at higher power levels. This behavior could be accounted for by the characteristics of the diodes used in the elements in the foreplane and by other considerations. One of the important possibilities taken into consideration was that the 5 elements in the foreplane were robbing power from their neighbors as the result of operating into a lower de load resistance. However, a wide variation of the de load resistance presented to the foreplane structure did not substantially perturb the aggregate power picked up by all the diodes in a central circular area whose diameter was larger than the length of the foreplane structure. To begin the experimental study of the integration of the foreplane into the 199 element array, it is noted that in the 199-element array all of the rectenna elements lie on sets of circles with different radii but with a common center. The common center is at the center of the array. Starting from the center, there is a single element at the center, designated set n0'f. There are six elements in Set No. 1 which has the smallest finite radius, six more in Set
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