cable

What is your real interest in? Do You want to measure the input impedance of the loaded cable? Or the wave resistance of cable as such is the subject of Your research?

i m a manufacurer of video cables. So one way is i maeasure the impedence by gemetrical parameters of the cable or other way i use vector network analyzer. So which method is recommended and what are the addditional information can i gather in second method??

I did not work in a field of radio-frequency cable production. Therefore my considerations can be not adequate to your problem. In my opinion, for on-line characteristic impedance testing in well organized industrial process it is quite enough to carry out geometrical measurings. However for more complete inspection it may become necessary an execution of radiofrequency measurements, including that with usage of VNA. In this case you, apparently, can reveal presence of inhomogeneities in a dielectric material and casual cable defects.

With instrumentation. Is this a homework from your school?