Since the transmission line must be used to transfer RF energy from one place to another, they need to be used. The most convenient and therefore the most common form of transmission line is a coaxial cable, which consists of two concentric conductors, an inner conductor and an outer conductor, commonly referred to as a screen. An insulating dielectric is present between the two conductors.

    Coaxial cables have many characteristics, one of which is characteristic impedance. In order to maximize power transfer from source to load, the characteristic impedance of both should match. Therefore, the characteristic impedance of the feeder is very important. Any mismatch will cause power to be reflected back to the source.

    It is also important that the characteristic impedance of the RF coaxial cable connector matches the characteristic impedance of the cable. If not, a discontinuity is introduced and may result in a loss.

    There are a variety of connectors for RF applications. Impedance, frequency range, power handling, physical size and many other parameters (including cost) will determine the best type for a given application.