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Subject: Dead Media Working Note 05.1

Dead medium: SHARP, a microwave-powered relay plane

From: (Jack Ruttan)

Source: the summary description of the SHARP project (May 1995), courtesy of Cecillia S. L. Cheung of the CRC (Communications Research Centre), Ottawa, Canada:

"SHARP - Stationary High Altitude Relay Platform


"SHARP is the acronym for the Stationary High Altitude Relay Platform that is a microwave-powered, unmanned aircraft designed to stay aloft for months at a time. To be situated physically between satellite and terrestrial facilities, the SHARP system offers new opportunities for communications, as well as a host of scientific and military applications.

"The SHARP system will utilize a high altitude unmanned airplane as a platform for collecting and relaying telecommunications and broadcasting signals as well as scientific and environmental information. The platform would circle slowly at an operating altitude of 20 km (70,000 ft) and relay signals over an area on the ground of 600 km in diameter.

"With this large coverage area, SHARP will provide a cost effective alternative for delivery of specialized communications services such as mobile and portable telephone, wide-area paging, radio trunking and TV and digital audio broadcasting. In addition, such applications as round-the-clock-surveillance of territorial waters, continuous long-term monitoring of the atmosphere, and remote sensing of the earth are possible.

"The innovative design feature of SHARP is the use of microwave signals transmitted from the ground as the source of propulsive power for the airplane. The entire underside of the aircraft is covered with thousands of printed circuit antennas which capture the microwave energy and convert it into direct current. This provides the power required to operate the platform's electric motor and payload."

(((end quote)))

The drawings show what looks like a t-tailed power glider, with wings on a pylon that also contains the tiny engine and propellor. There is no place for a pilot, of course, and the other big difference is a huge disk mounted on top of the fuselage taking up nearly the entire length of the craft between wing and tail, making it look something like an AWACS plane. This disk is covered underneath with microwave collector cells, as is every other surface on the underside of the aircraft, including the flattened bottom of the fuselage. A pair of rodlike antennas stick out from the nose of the aircraft, swept back like the whiskers of a cat. The wingspan would be 25 metres.

The ground array of antennas would measure 80 metres in diameter, and put out approximately 500 Kw of microwave power, focussed in a beam of 20 metres diameter aimed at the aircraft 20 Km up in the air.

A 1/8 scale prototype developed by the CRC flew on Sept 17, 1988, at 0720h, for twenty minutes. It ultimately reached flight times of up to 95 minutes, after some difficulties.

I quote from the paper presented at the IEEE MTT-S International Microwave Symposium, New York, N.Y., May 25- 27, 1988 by Joseph J. Schlesak, Adrian Alden and Tom Ohno: A MICROWAVE POWERED HIGH ALTITUDE PLATFORM:

"Investigations found [...] that a rectenna with this format had serious limitations in many power transmission scenarios. One of these disadvantages stemmed from the use of linear dipoles for the antenna array. For the powering of moving platforms, or in cases of depolarization due to Faraday rotation rain etc., the transmission antennas, providing the power beam, would have to have polarization track to stay aligned with the dipoles on the platform, a costly and complicated process.

"Another limitation, and of major concern, were the high levels of radiated EMI observed from VHF to beyond S-band. The Schottky diodes, used for microwave to dc conversion, exhibited intermediate frequency (I.F.) negative resistance when 'pumped' at 2.45 GHz by the powering beam, causing spurious oscillations. These high levels of EMI could interfere with payload and platform electronics, as well as distant electronic systems."

(((end quote)))

Though the project was intended to be developed through 1995 to the year 2000, according to Cecillia Cheung, (who graciously and very promptly provided me with hard copy of all this information) work on it has been terminated at the CRC due to lack of funds. Via e-mail, Ms. Cheung informs me that CRC owns several patents related to the project, research is taking place at institutions in other countries, and such programs usually take from 20 to 30 years to 'get off the ground.' "Just for your information, this is NOT a 'dead media' project," she stresses.

I thought you'd want the information anyway.

See: A. Fisher "Beam-Power Plane", Popular Science, Vol. 232, No. 1, pp. 62-65, January, 1988.

CRC is on the web at

Jack Ruttan

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