A THEORETICAL STUDY OF MICROWAVE BEAM ABSORPTION BY A RECTENNA James H. Ott - James S. Rice - Donald C. Thorn Novar Electronics Corporation - Barberton, Ohio Power Beam Absorption The Rectenna's microwave power beam absorption limit is theoretically confirmed to be 100%. Two mathematical models descriptive of the microwave absorption process were derived from Maxwell's equations. The first model is based on the current sheet equivalency of a large planar array above a reflector. The model is characterized by a mathematical expression for the fraction of an incident plane wave's power that is reflected from the sheet. The second model, which is based on the properties of a waveguide with special imaging characteristics, quantifies the electromagnetic modes (field configurations) in the immediate vicinity of a Rectenna element in the Rectenna array. This model then gives the limits for element spacing which permit total power beam absorption by preventing unwanted modes from propagating (scattering). Rectenna Design Improvements Several improvements in the Rectenna design have been indicated by the mathematical modeling. 1. A significant reduction can be made in the density of the Rectenna elements needed for total beam absorption. This would not only significantly reduce the cost of the Rectenna but also indicates greater diode efficiency because of the higher power density per diode. 2. The Rectenna panels can be made to totally absorb at any angle of incidence by adjusting reflector and element spacing and load impedance as seen by the dipole elements. This suggests a flat or terrain conforming Rectenna eliminating the need for the "billboard" or "Venetian blind" design and essentially conforming to the terrain. 3. The screen reflector should be able to be replaced by parasitic reflector dipole elements.
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