3.0 RECTENNA ELEMENT CIRCUIT MODIFICATIONS 3. 1 Introduction The activities reported upon in this section are as follows: (1) Modification of the circuit of the rectenna element to permit more efficient operation at lower input power levels. This was the principle effort in this section. (2) The first steps in the integration of the basic RXCV rectenna element into a configuration consistent with the two-plane rectenna construction in which nearly all of the basic functions of the rectenna are carried out in the front plane to facilitate a much more economical form of construction. (3) Investigations into reducing the second and third harmonic radiation from the rectenna element by the use of stub lines tuned to the harmonic frequencies. One of these stub lines is naturally present in the two-plane rectenna concept. (4) Investigation of the role of metallic shielding to improve the efficiency and reduce the radiation of harmonic power. (5) Improvements in efficiency by refinements in the construction symmetry of the RXCV element. 3. 2 Circuit Modifications to permit more efficient operation at reduced microwave power input levels. 3.2.1 Introduction and summary of results The motivation for this activity was the conclusion reached after making a study of the microwave transmission system of a solar power satellite system (26) that most of the area of the rectenna in a full scale SPS would be operated at power density levels that are low compared to those of the RXCV at Goldstone. At these low input power levels, the standard RXCV rectenna element gave considerably lower efficiency than that obtained at the higher power levels. It was therefore logical to direct a portion of the effort under this contract to improving these efficiencies. The efficiency objective of this technology development contract was 85% at an input power density level of 1 to 100 mW/cm (2450 MHz). Since the cell area occupied by a rectenna element is very close to 50 square centimeters, this objective translates into a power input range to an individual rectenna element of 50 milliwatts to 5. 0 watts. Prior to the undertaking of work under this contract an approximate expression had been developed for diode efficiency in terms of important diode parameters, and the value of the load resistance. These led to an
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