[COham] Salt Water Antenna

[Paul Signorelli]

You all recall Jake's (N0LX) QRP Salt Water Antenna..
He built it in his front yard a few years ago...
You might thought he was going  off the deep end of the pier... but read this...!!!

Editorial from HF Electronics, Nov. 2019, by Tom Perkins.

Recent disclosures of new antenna technology are quite innovative and perhaps disruptive. First there is an antenna claiming advantages over metal antennas that uses salt water and plastic for beamforming. There are obvious advantages in being able to shape vertically polarized beams for increased point-topoint range and minimal interference in unintended azimuth directions. Beamforming will play a significant role in implementation of 5G networks. Beam steering employing agile patterns such as variable beamwidths for communications with single or multiple cellular devices in a general direction is very desirable. Certainly not the first liquid antennas, these antennas are quite reconfigurable and may be feasible from at least 30 MHz to 3 GHz. Lei King and her colleagues at Nanjing University of Aeronautics and Astronautics have proposed an array that has 12 directional beam-steering states along with an omnidirectional capability. It works over a full 360 degrees with beam steering for UHF frequencies from 334 to 488 MHz. The design consists of a circular ground plane, with 13 vertical transparent acrylic tubes that can be filled with salt water to a reflective or perhaps also directive resonant length. Each tube can also be emptied (drained) on demand. One tube is located in the center of the circular array to act as a driven element monopole via a copper disk at the base of the tube. Surrounding it are 12 parasitic monopoles. When only the driven monopole is excited an omni-directional pattern exists. The 12 remaining monopoles, when filled appropriately to a tuned height with salt water, work to give the antenna pattern direction. The array of vertical tubes has a liquid control system using micropumps, likely computer controlled. Salt water height and activating status can be dynamically tuned, which is quite superior to most metal antenna tuning techniques. When the antenna is switched completely off and drained, it is nearly undetectable by radar. A limitation of salt water-based antennas is that the permittivity of saline water, which determines how it interacts with electric fields, is sensitive to temperature variation. Also, if this scheme were to be applied in an environment lacking gravity, special provisions likely adopted from space travel water supply systems would likely be needed. This design reminds me of a circular multiple antenna device I observed at Thayer School of Engineering at Dartmouth College. That effort is led by Professor Paul M. Meaney, IEEE Fellow. This is a circular array of metal—not salt water—vertical monopoles on the perimeter stimulated sequentially with microwave energy with the other elements in the circle acting as receiving antennas in a programmed sequence. While somewhat similar in appearance....
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