by knowing the frequency of the signal you can easily find the complex impedance
check the manufacturer's guide for the inductance and capacitance coefficient of the cable from them calculating the complex impedance part is very easy
just try it and post
i have also not tried this so just stating a possibility
The transmission line impance can be calculated from the R'L'C'G' per unit length.
See here, telegrapher's equation:https://en.wikipedia.org/wiki/Transmission_line
You can simulate or measure a short line segment, with length 1/20 wavelength or less. From that, you can extract the RLCG values and calculate Z0. I have documented an example here, pages 6-8. https://muehlhaus.com/wp-content/uploads/2011/08/Analysis-of-RFIC-Transmission-Lines.pdf
This well known equation is valid only for perfectly shielded transmission lines whatever type is.What about radiating or non-perfectly shielded-for instance coaxial transmissin lines?
The transmission line impance can be calculated from the R'L'C'G' per unit length.
See here, telegrapher's equation:https://en.wikipedia.org/wiki/Transmission_line
You can simulate or measure a short line segment, with length 1/20 wavelength or less. From that, you can extract the RLCG values and calculate Z0. I have documented an example here, pages 6-8. https://muehlhaus.com/wp-content/uploads/2011/08/Analysis-of-RFIC-Transmission-Lines.pdf
depend not only on the frequency, but also on the length of the structure.
Here's my structure.
which I will call a "pseudo-coax", for want of a better word. The brown/orange inner conductor is centrally located between the 4 blue outer conductors. The ring at the top just joins the 4 outer conductors together.
The fact the structure is open will mean it will radiate.
Deborah
The fact the structure is open will mean it will radiate. - I don't think this is correct. An open balanced two conductor transmission line has a real characteristic impedance and doesn't radiate, an open microstrip line in homogeneous medium (no dielectric) is TEM and doesn't radiate...
Your 'pseudo-coax' has some characteristics similar to a twin-wire transmission line. It has fields outside the line, these will not radiate for an infinite straight run. Lossy items in these fields will cause losses, and conductors may couple to these fields and cause radiative losses.
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I fear, this is a simplification, too. Open transmission lines will radiate at least at any discontinuity, that's e.g. the principle of a leaky feeder. And as far as I remember, there's a certain coupling between the open TEM wave and free space, simply because the open TEM wave extends into free space without bounds.I don't think this is correct. An open balanced two conductor transmission line has a real characteristic impedance and doesn't radiate, an open microstrip line in homogeneous medium (no dielectric) is TEM and doesn't radiate...
I fear, this is a simplification, too. Open transmission lines will radiate at least at any discontinuity, that's e.g. the principle of a leaky feeder. And as far as I remember, there's a certain coupling between the open TEM wave and free space, simply because the open TEM wave extends into free space without bounds.
If you are going to design a real open coax line with finite length and discontinuities at least at the ends, there's no alternative to perform a numeric EM solution if you want to know the exact properties.
You can use the technique of measuring the impedance at one end of a length of cable with the other end successively open and shorted. Let those impedances be Zoc and Zsc; then the characteristic impedance of the cable is given by Zo = SQRT(Zoc*Zsc).
If you are working in RF you should have access to a vector network analyzer. I took a 1 meter piece of small, lossy, nondescript small diameter (probably lossy) coax from a big roll I bought at Boeing surplus and connected one end to a VNA. I swept the frequency from 100 kHz to 200 MHz and displayed the impedance on a Smith chart.
I forgot to say that I would be interested to hear what results you get if you are able to perform these measurements, and to see an image of the Smith chart plot for your leaky cable.
Draw the structure in any EM modeling software. Simulate it and you will get the impedance on the Smith chart !
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