RF cable Propagation Delay time vs. Frequency

Salam,
does the delay time introduced by RF cable varies with frequency ? if yes, what is the formula?

velocity = speed of light /sqrt(Er). Er is a property of the cable internal insulation and is frequency dependent. the variation in Er over frequency depends of the material. time delay is velocity/distance.

I understand that the question refers to technical RF cables using PE or PTFE dielectrica. The propagation speed is effectively constant down to several ns/m decimal places, so manufacturers don't specify any frequency dependance for it.

What type/length of RF cable are you using? What is the frequency range?

Without additional information, it would be difficult to specify an exact equation which your cable will obey.

You might want to perform a search on the topic of 'Dispersion in RF cables'. Here is a report on the topic [ http://www.ece.vt.edu/swe/lwa/memo/lwa0136.pdf ], which provides a relation between the delay time and frequency.

@ jeeudr:
i will be using Coaxial cable(most probably RG-405) any my delay requirement is the range (75 pico seconds to 100 pico seconds)..my frequency range is 200 MHz to 4.2 Ghz....does delay remain nearly constant over this broadband range...?

The amount of delay a transmission line introduces per distance x is:

Time Delay = x / Vp = (βx / ω)

where β is the phase shift in degrees, and Vp is the velocity

the delay time thru a physical cable does vary slightly with frequency, but to a first order it is constant