A fan dipole solves the multi-band problem with an approach that’s almost embarrassingly simple: instead of one antenna trying to cover several bands through traps or compromise, you just hang several resonant dipoles off the same feed point.
The concept
A fan dipole is exactly what it sounds like: multiple individually cut, resonant half-wave dipoles, each for a different band, all connected to the same feed point and center support, fanning out at slightly different angles to keep the wires from touching. Because each leg is independently resonant on its own band, there’s no trap loss and no compromise tuning, each dipole simply does its job on its own frequency while presenting a high enough impedance on the other bands to stay mostly out of the way.
Where it gets tricky
The wires do interact with each other more than the simple description suggests, especially between adjacent bands like 40 and 20 meters where harmonic relationships cause more coupling. Getting a clean SWR on every band usually takes some trimming and iteration, adjusting one dipole leg can shift the resonance of another slightly, and keeping the legs physically separated at the ends, whether by spreading them at different angles or using separate support points, matters more than it looks like it should on paper.
Fan dipole vs trap dipole
Compared to a trap dipole, a fan dipole avoids trap loss entirely and tends to have better bandwidth on each band since every leg is genuinely resonant rather than electrically shortened. The tradeoff is more wire, more end supports (or a wider single support point spread), and a somewhat fussier trimming process to get every band dialed in cleanly. For a permanent multi-band installation where you’ve got the space for the wider antenna profile, I’d generally choose a fan dipole over a trap dipole for the efficiency alone.
Related reading: The G5RV and Windom · Trap Dipoles and Verticals · Full-Size Wire Loop Antennas