over a comparatively wide range of input power levels. The maximum average power level of the elements in the foreplane structure was 4.34 watts. Higher levels were not sought in order to minimize the possibility of diode failure, since these diodes do not have a particularly high reverse breakdown voltage. The data shown in Figure 5-15indicate that the power output of foreplane structure has a close linear relationship to the incident power level, as does the formula for the predicted power level which is composed of experimental inputs from Sets 1 and 3. Because portions of Sets, 1, 2, 3, 4, and 5 interact with the foreplane structure, it is of interest to see how the power outputs of these sets behave as a function of the de load resistance placed upon the 5-element foreplane structure. Figure5-16 shows the aggregate power output of the foreplane structure plus the power outputs of Sets 1, 2, 3, 4, and 5 all of which have some mutual coupling impedance to the foreplane structure, as the de load resistance of the foreplane structure changes from 25 to 41 ohms. The aggregate power rises by 2% over this range. The behavior of the individual power in the sets is also shown in Figure 5-16. As the load resistance of the foreplane structure is increased, the power output of the foreplane structure decreases by about 4% while the power in sets 1 and 2 increases by about 4%. Sets 3 and 5 are relatively unchanged. Set 4 has an increase of about 2%. The qualitative observation is that the perturbation of the aggregate power and the individual set powers is not greatly influenced by the de load resistance of the foreplane structure. However, it is noted that the agreement between predicted foreplane power and experimentally observed values is a function of the foreplane de load resistance. This relationship is shown in Figure 5-17. The total aggregate power increase as a function of the foreplane de load resistance may be correlated with a decrease in reflected power as determined by VSWR ratio measurements with a probe in front of the center of the 199-element by VSWR ratio measurements with a probe in front of the center of the 199-element array. The validity of this kind of measurement is good if the illumination is gaussian and if the percentage of power reflected is uniform over the array. In the efficient operation of the 199-element array, the elements in each set are trimmed for minimum reflected power at the power level at which they are intended to operate. The reflection loss that is experienced when they are operated at other power levels is suggested by Figure 5-11. In the illumination of the rectenna in which the foreplane is incorporated, the incident power level is different on the five elements, although they share a common load. Hence, the situation for making VSWR measurements is not ideal, particularly in close proximity to the three central elements of the foreplane structure where these elements will dominate the reflected power. However, if the probe is backed off, the VSWR ratios become more valid. Under these conditions, the VSWR associated with a 25-ohm load is 2.8 dB as compared with 1. 5 dB for the 40-ohm load as shown in Figure 5-18. The corresponding
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