What is a Multiband HF Fan Dipole Antenna?

What is a Multiband HF Fan Dipole Antenna?

Fan dipole uses a group of parallel dipoles for different Amateur Radio bands fed from the same feeder coaxial cable so that the elements fan out from the feed point to either side. Impedance of each dipole is low at its resonant frequency and high at other frequencies. So a 40 m dipole does not absorb much power at 20 m. Each element to either side will have a length corresponding to the quarter wavelength of that frequency. Fan dipole can be mounted as a horizontal dipole or in an inverted V configuration if there is space constraints.

The different elements should not correspond to odd multiple frequencies like 7 MHz and 21 MHz. In that case both will have low impedance at 21 MHz. The elements of different bands need not be parallel, but will need additional anchors in that case. Parallel elements do not need additional anchors, but need insulators to keep them spaced. Dipoles are balanced while coaxial feeder is not. Hence a balun is needed at the feed point to prevent the outer conductor of the coax from radiating RF power.