What is a Rotary Dipole Antenna?

Just as the name implies, it is a dipole antenna which can be rotated so as to optimise the direction of transmission and reception. We know that a dipole antenna has some directivity along its broad side with minimal radiation along the ends. That is why we say that the radiation pattern of a dipole is dumb bell shaped and that it has a gain of 2.15 dBi with respect to an isotropic antenna which is a theoretical antenna with uniform spherical radiation pattern in all directions. Unlike usual half wave dipole antennas in amateur radio which are made of wires, rotary dipole antennas have to be sturdy so that it remains horizontal and can be rotated. It should also be able to accept some wind loading without damage. While a horizontal dipole antenna needs two supports, a rotary dipole needs only one support in the center. Rotary dipoles are often made of aluminium tubings to reduce the weight, to make it suitable for mounting and rotation.

Several commercial versions of rotary dipoles are available. They are often electrically shortened with loading coils to make them fit in smaller available space. Unlike a usual horizontal dipole which need to have free space only along the line of fixed mounting, a rotary dipole needs space along the radius of a circle for rotation, which could be a disadvantage in homes with very little space around. Electrically shortened dipoles are useful in such situations. Of course too much shortening with loading coils will reduce the bandwidth of the antenna and reduce efficiency due to power lost in the resistive components of the coils which are much thinner than the horizontal radiating elements. Multi-band rotary dipoles with rotator and controller are also available commercially. I could find options for 10-40m and 6-20m online.