Rik,

People have used ribbon cable to make loops. The wires are offset at the ends and jumpered in header connectors so there's a continuous circuit. Not sure about the turns spacing, but sure is easy to set up and stow away. A double-umbrella arrangement might work, but would be mechanically fragile with non-conductive material.

73,

Jim, KR1S
http://qrp.kearman.com/