Two conductors can create a transmission line. To make an effect transmission line with two wires it is best to create a twisted pair. Often when working with wires it is easy to create large return path loops if one is not paying close attention. The twisted pair helps create a more uniform inductance and capacitance per unit length of wire to ensure a constant impedance, by keeping the return path as close to the signal as possible.
The geometries of the twisted pair that we should pay close attention too are the distance between the two conductors (center to center) and the diameter of the conductive wire. The effective permittivity of the material between the two conductors will be somewhere between the permittivity of the insulation on the wires and the relative permittivity of air (1).
Models have been created to approximate the characteristics of the microstrip transmission line.
 Cable Impedance
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