Different antennas have different feed point impedance, and sometimes the most typical ununs (or baluns) can not match well such an antenna with 50 ohm coax. That's why I decided to gather a number of unun designs in one place for my own reference. Perhaps, the other antenna designers will find it useful too.
The ununs shown below allow you o match antennas of various feed point impedance. They should be wound on ferrite ring cores having low loss in the frequency range of interest.
Please mind that the ununs shown below do not attenuate the common-mode current. If it is required, add a 1:1 current balun (a.k.a. common-mode choke or RF choke) between the 50 ohms port and the coaxial cable. Such balun can be conveniently wound over a ferrite ring core with a piece of thin 50 ohms coax cable.Â
The unun can also be used in the matching network of a symmetrical antenna. In such application, a 1:1 current balun needs to be added between the output port of the unun and the antenna.