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This topic is offered for NewMars members who might wish to post links, images or text about rectenna design, manufacture, application, function or anything else that might be of interest to our readers.
The topic is inspired by a post in late June, 2025, by Void, in which Void introduces the innovative idea of using a rectenna on the underside of a balloon to receive microwaves from a ground based transmitter to provide power for acceleration to LEO.
The first use of the term "rectenna" that ** I ** remember is their use in the context of designs for Space based Solar Power ("SPS")
In that context, the rectenna was envisioned as a field of receiving dipoles large enough to collect the microwave energy beamed down from a satellite in GEO (Geosynchronous orbit). Due to the distances involved, that would have been a large field, because microwaves (like all normal electromagnetic waves) disperse.
In the context of a much smaller receiving field such as the underside of a balloon, it would be necessary for the microwave transmitters on Earth to focus energy as tightly as possible on the receiving dipoles. however, the distances involved are on the order of 100 or 200 kilometers, compared to the many thousands of kilometers the GEO SPS designers were considering, so focus at that level may be possible.
In addition, since the balloon would be accelerating in order to achieve LEO, it would require a network of microwave transmitters able to provide the narrow beam for as long as the balloon is in range. Never-the-less, this seems to me to be an idea worth developing.
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Someone with an electronics engineering background might find development of an entire system for this purpose rewarding. The context is provided in Void's report on the ongoing work of John Powell (JP Aerospace). Mr. Powell has been leading an effort to fly a balloon to space for decades.
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Post #2: Wikipedia article on Rectennas
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To lead off, here is a snippet from the Wikipedia article on Rectennas:
https://en.wikipedia.org/wiki/Rectenna
From Wikipedia, the free encyclopedia
A rectenna (rectifying antenna) is a special type of receiving antenna that is used for converting electromagnetic energy into direct current (DC) electricity. They are used in wireless power transmission systems that transmit power by radio waves. A simple rectenna element consists of a dipole antenna with a diode connected across the dipole elements. The diode rectifies the AC induced in the antenna by the microwaves, to produce DC power, which powers a load connected across the diode. Schottky diodes are usually used because they have the lowest voltage drop and highest speed and therefore have the lowest power losses due to conduction and switching.[1] Large rectennas consist of arrays of many power receiving elements such as dipole antennas.Image: A printed rectenna lighting an LED from a Powercast 915 MHz transmitter, flexible meshed antenna bent with a red LED light
Image: A printed meshed rectenna lighting an LED from a Powercast 915 MHz transmitter
Power beaming applications
The invention of the rectenna in the 1960s made long distance wireless power transmission feasible. The rectenna was invented in 1964 and patented in 1969[2] by US electrical engineer William C. Brown, who demonstrated it with a model helicopter powered by microwaves transmitted from the ground, received by an attached rectenna.[3] Since the 1970s, one of the major motivations for rectenna research has been to develop a receiving antenna for proposed solar power satellites, which would harvest energy from sunlight in space with solar cells and beam it down to Earth as microwaves to huge rectenna arrays.[4] A proposed military application is to power drone reconnaissance aircraft with microwaves beamed from the ground, allowing them to stay aloft for long periods.
A wearable millimeter-wave textile rectenna fabricated on a textile substrate for harvesting power in the 5G K-bands (20–26.5 GHz)
In recent years, interest has turned to using rectennas as power sources for small wireless microelectronic devices. The largest current use of rectennas is in RFID tags, proximity cards and contactless smart cards, which contain an integrated circuit (IC) which is powered by a small rectenna element. When the device is brought near an electronic reader unit, radio waves from the reader are received by the rectenna, powering up the IC, which transmits its data back to the reader.
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In the context of Void's vision, of providing power to one of JP Aerospace's designs for a space going balloon, I would like to offer the suggestion that the balloon might be shaped like a wing so that the underside is large enough to hold acres of rectenna devices, while at the same time having a shape well suited for deflecting molecules downward as they are encountered during flight.
In John Powell's design, the balloon that flies to space will never descend lower than a base station at a very high altitude.
Void's suggestion for use of microwaves to beam power might provide a convenient way to provide power for the high altitude station. The difference in that case is that the balloon would be stationary.
A related application for such a high altitude station is the ability to provide communications or observation services.
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Last edited by NewMarsMember (2025-06-27 06:39:50)
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