RF like to travel within a circuit with a consistent characteristic impedance. Any changes in characteristic impedance will produce signal loss. Characteristic impedance Z is essentially a measure of resistance. It has three components that are added vectorially. The components are: the pure DC resistance in the x- axis, the inductive reactance in the y-axis, and the capacitive reactance in the z-axis. The characteristic resistance is calculatd all along a given signal path and any change in any one of the 3 above resistances at any point will alter the resistance. 50 ohms (Ω) is the most generally accepted resistance in most RF circuits.