A report on Electrical length and Stub (electronics)

Neglecting transmission line losses, the input impedance of the stub is purely reactive; either capacitive or inductive, depending on the electrical length of the stub, and on whether it is open or short circuit.

When one is concerned with the number of wavelengths, or phase, involved in a wave's transit across a segment of transmission line especially, one may simply specify that electrical length, while specification of a physical length, frequency, or velocity factor is omitted. The electrical length is then typically expressed as N wavelengths or as the phase φ expressed in degrees or radians. Thus in a microstrip design one might specify a shorted stub of 60° phase length, which will correspond to different physical lengths when applied to different frequencies. Or one might consider a 2 meter section of coax which has an electrical length of one quarter wavelength (90°) at 37.5 MHz and ask what its electrical length becomes when the circuit is operated at a different frequency.