Patent No. 5218374 Power beaming system with printer circuit radiating elements having resonating cavities

 

Patent No. 5218374

Power beaming system with printer circuit radiating elements having resonating cavities (Koert, et al., Jun 8, 1993)

Abstract

A system and method for "power beaming" energy from a source at high frequencies and rectifying such energy to provide a source of DC energy is disclosed. The system operates at a frequency of at least 10 GHz and incorporates a rectenna array having a plurality of rectenna structures that utilize circuit elements formed with microstrip circuit techniques. Each rectenna element is associated with a resonating cavity structure.

Notes:

BACKGROUND OF THE INVENTION

The present invention relates in general to the transfer of energy by means of electromagnetic waves to power a remote device. More specifically, the present invention relates to a system for "power beaming" energy from a source at high frequencies and rectifying such energy to provide a source of DC energy to a remote device.

Attempts have been made for many years to develop a system for beaming energy from a source to power a remote device with a high degree of efficiency (for a general discussion see "The History of Power Transmission by Radio Waves" by William C. Brown, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-32, No. 9, September 1984). In particular, the concept of powering a satellite or free flying aircraft by power beaming has received a great deal of attention. The advantages of such a system are readily apparent, for example, an aircraft could be maintained on station indefinitely to act as a low cost communications or reconnaissance platform. Early concepts included the conversion of microwave energy into thermal energy to power a helicopter type platform as illustrated in U.S. Pat. No. 4,542,316 issued to Hart. A more practical approach, however, has focused on converting the microwave energy into DC energy to directly power the platform.

The practical conversion of microwave energy to DC energy for power beaming purposes has been based on the use of rectennas to receive and rectify the microwave energy. Generally, rectennas are limited in their power-handling capabilities, but can be a highly efficient means of converting microwave energy into DC energy for power beaming purposes when employed in large numbers in an array structure. U.S. Pat. No. 3,434,678 issued to Brown et al. illustrates the use of a rectenna array to power a helicopter platform by power beaming.

More recently, a scale model of a long endurance high altitude platform powered by microwave energy known as SHARP (Stationary High Altitude Relay Platform) has been successfully demonstrated. See "A Microwave Powered High Altitude Platform" by Schlesak et al., 1988 IEEE MTT-S Digest, pp. 283-286. The SHARP concept calls for an array of ground antennas which must be focused on the aircraft. The underside of the aircraft would be coated with a thin-film array of thousands of half-wave dipole rectennas to convert the received microwave energy into DC energy which would be used to power the aircraft's electrical motor.

The scale model of the SHARP aircraft was powered by a microwave beam formed form the outputs of two 5 kW continuous-wave magnetrons, which were combined and supplied to a 4.5 meter diameter parabolic antenna to transmit 10 kilowatts of energy at a frequency of 2.45 GHz. Dual polarization rectennas formed of two orthogonal linearly-polarized rectenna arrays were provided on the model aircraft to convert the microwave energy to DC power.

Efforts at power beaming to date, like SHARP discussed above, have focused primarily on using S-band transmission sources due to their ready availability and to reduce power losses due to atmospheric attenuation. S-band power beaming, however, is limited in the amount of power that can be delivered in a practical system. In order to generate sufficient power densities, a large array of ground antennas must be employed which complicates the problem of concentrating the transmitted energy on the aircraft. One could reduce the number of ground antennas employed in the array, but the size of the antennas would increase significantly making them as difficult to track as the array while greatly increasing their expense. In addition, S-band power beaming requires a large amount of surface area for the rectenna array on the aircraft to generate significant power quantities. For example, the SHARP system discussed above would need an array of 100 m.sup.2 of rectenna surface of generate only 35 kW of DC power, 25 kW of which is required to power the propulsion system, wile requiring a transmitter having a diameter of 85 meters with an output of 500 kW.

SUMMARY OF THE INVENTION

The present invention departs from the prior art by providing a power beaming system that operates at a much higher frequency, on the order of tens of GHz or greater, to thereby provide a system having a power density an order in magnitude greater than conventional power beaming systems while at the same time having the advantage of a smaller transmission source and rectenna array.

More specifically, the present invention provides a power beaming system including a power transmission source capable of generating electromagnetic radiation having a preferred frequency of at least 10 Gigahertz, a transmission antenna mounted on a movable pedestal, a guide unit that guides the electromagnetic radiation generated by the power transmission source to the transmission antenna and a rectenna array located at a position remote from the antenna structure.

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It will be readily understood that variations and modifications may be made within the spirit and scope of the invention as expressed in the appended claims, and that the invention is not limited to the specific forms illustrated above. For example, monolithic microwave integrated circuit (MMIC) technology can be used to fabricate top layer 100 and insulating layer 100. The top layer 400 could consist of gallium arsenide with conductive coating 220 deposited on one side, and the diodes, 320, antennas 310, and feed lines 330 deposited on the other. Insulating layer 400 would be the final deposited material. The resonating cavity structure 450 could be included using either monolithic technology, or bonded to the surface of the insulating layer 400 to create a hybrid microwave integrated circuit (HMIC).