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Subject: Dead Media Working Note 05.1
Dead medium: SHARP, a microwave-powered relay plane
From: jackr_AT_intrepid.axess.com (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
"OVERVIEW OF SHARP
"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 http://www.crc.doc.ca/
Jack Ruttan jackr_AT_intrepid.axess.com
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