Measuring the Electrical Length of a trans. line

Hello

I have a line made out of several components (all quaxial),
I measured its attenuation (-13dB) , and its physical length.
However I must know its electrical length in order to replace it with only one equivalent line.
I need to know it only for a range of 1.9-2.3GHz.

How do i measure the electrical length?
(i can measure frequency response with spectrum analyzer S21)

Thanks in advance.

Hook you're signal source (tracking generator if your spectrum analyzer has one), spectrum analyzer, and cable in a T configuration. If the cable is open-ended you're first null in the response is at 1/4 wavelength.