Air core coils are widely used in electronic circuits. They are characterised by consistency in their inductance value.
These are coils usually rolled by solid conductors, self-supported or rolled on insulating materials with the aim that the winding takes a specific shape.
Their inductance, L, can be calculated with a good approximation. The stray or distributed capacity is minimal since an extreme is separated from another and separation between spires can become big.
Furthermore, the proximity effect is very low so that high Q levels can be obtained and used in high frequency products.