rectenna element over a wide range of power levels. The efficiency of the rectenna element as measured by the ratio of DC power output to microwave power absorbed is seen to vary from a low of 56% at 100 milliwatts of incident power to 90.5% for a power input of 8 watts. The diode losses are observed to vary from 36% to 7.4% of the absorbed microwave power. The circuit losses are assumed to remain constant at 2.62%. When the DC power output is added to the sum of the diode losses and circuit losses the total sum as represented as a percentage of the absorbed microwave power is seen to be very close to 100% and within the probable error of 0. 75% previously established, over an appreciable portion of the range of input power levels examined. All of the data given in Table 2-1 was obtained with the use of the ground-plane test fixture shown in Figure 2-2, since the diode loss measurements can only be made with the aid of this test fixture. The measurements were also made with the use of diode 40593-CPX1G #13 which was one of the standard reference diodes obtained from the RXCV program. The Schottky barrier was platinum on Gallium Arsenide. A metallic shield was placed over the rectenna element to improve the efficiency. Most of the information given in Table 2-1 is given in graph form in Figure 2-10. Of especial interest is the manner in which the diode losses are shown to vary in Figure 2-10. The diode losses follow very accurately a curve described by the equation; across the Schottky barrier to the total de voltage developed. For good efficiency it is obvious that this voltage drop should be as low as possible, and this is the prime reason for shifting to a GaAs-W barrier in the Schottky diode.
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