A new very compact VLF antenna concept has been developed by the Department of Energy. I wonder if this would be economically reproducible for amateur VLF or even 160 meters? The full article is available from phys.org at: https://phys.org/news/2019-04-slac-compact-antenna-radios.html It says, in part: A new type of pocket-sized antenna, developed at the Department of Energy's SLAC National Accelerator Laboratory, could enable mobile communication in situations where conventional radios don't work... While today's most powerful VLF technology requires gigantic emitters, this antenna is only four inches tall... "Our device is also hundreds of times more efficient and can transmit data faster than previous devices of comparable size," said SLAC's Mark Kemp, the project's principal investigator. "Its performance pushes the limits of what's technologically possible and puts portable VLF applications, like sending short text messages in challenging situations, within reach."