While these can be home-brew, the traps are rather difficult to build and adjust so most amateurs use commercial versions. These traps electronically isolate sections of the antenna at higher frequencies thus making the antenna resonant on these other bands. They are directional antennas thus most of your radiated power can be concentrated in a single direction. They also will help significantly on reception. They do have the drawback that when you consider that you must also invest in a tower or mast and an antenna rotor, you can have quite a lot of money invested in a beam antenna system, and you still have no antenna for 80 and 40 meters.
T here are several multiband vertical antennas commercially available.
Both have an optional 80 meter add on. While expensive, this system would cost significantly less that a beam antenna system. T he antenna I use is a non-resonant multiband dipole and works reasonably well on all the HF amateur bands from 160 meters to 10 meters. A misconception is that an antenna must be of a resonant length to function and this is simply not so. This stems from the fact that most all ham radios have a 50 ohm output impedance.