the losses in the rectenna element. This was done by developing a procedure to measure the losses in the diode, which was determined to be the principal loss mechanism, and developing a procedure based partly on experimental measurement of losses and partly upon computer simulation to determine the circuit losses in the rectenna element. As a result of this procedure there is a much greater confidence in the probable error of efficiency measurements established on the basis of calibration procedures originating with the Bureau of Standards and transferred by suitable means but with an estimated error to a test arrangement for measuring rectenna element efficiency. The probable error in efficiency measurements is ±0. 6% for measurements over 100 milliwatts, and ±0.4% for measurements at 100 milliwatts. There was an improvement effected in resolution of efficiency measurements by using a digital meter on the microwave power input measurement and a digital voltmeter to measure the DC voltage across the carefully calibrated DC load resistance. It was also determined that the reproducibility of efficiency measurements depended heavily upon the electrical and mechanical symmetry of the rectenna element itself. Higher order modes in the expanded wave guide test fixture can also be a minor source of measurement difficulty depending upon the coupling symmetry of the rectenna element and upon the frequency of testing. This is a characteristic of the test fixture itself and would not be experienced in the use of the rectenna element in the rectenna array. 3. Quantitative Evaluation of Losses in the Rectenna Element Prior to this contractual effort only engineering estimates of the quantitative values of loss mechanisms in the rectenna element were available. Under this contract a highly accurate method for experimentally determining the total losses in the diode was developed. Experimental measurements were also made on the losses in the input low pass filter section of the rectenna element. Losses in the rectifier tank circuit were obtained from the computer simulation program. The measured losses in the diode agreed with previous engineering estimates. The minimum total losses in the diode were found to range from as low as 7.4% of the input power for microwave input levels of several watts to very high values for very low power inputs. At very low power inputs there was a substantial error involved in the experimental method. Circuit losses other than those taking place inside the diode were found to be in the region of 2 to 3%. The probable error in these
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