AIR CORE COILS
They have a utility, quite generalized in electronic circuits. It is characterized by the constancy in its inductance value. These are coils normally wound by solid conductors, remaining self-supported or wound on insulating materials so that the winding adopts a specific shape.
Its inductance, L, can be calculated with a good approximation. The parasitic or distributed capacity is minimal since one end is separated from the other and the separation between turns can become large. Furthermore, the proximity effect is very low so that high Q values can be obtained and used at high frequencies.