The width and rise time are determined based on the frequency range entered when creating the CST project. Zo=50Ī normalized Gaussian pulse is the excitation signal by default at the ports. Outer and inner diameter is 5.7 and 1.7 mm with PTFE dielectric (Er=2.1). Increasing in 1 mm or so the Z distance of the background should solve the problem. Maybe geometry is too complex or mesh is too coarse in this region. “Staircasing failed for discrete edge port “2”: discrete edge port “2” is completely inside metal material. When the background box (black wire frame) encloses tightly the model geometry and you are using a discrete port then you can have the solver complaining like this: You can set the impedance of the port to a value other than 50 Ohms. One would be interested in doing so if the purpose is to see the effect of a sudden change in characteristic impedance. A helpful remark is that one of the waveguide port (the red squares in the model) can be replaced by a discrete port.
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The model is as shown in the image below (also available to download here).
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The process is very easy with CST, plus tutorials are readily available to help start. Simulating a coax is something that will surely not rack your brains. As with any 3D modeling tool, the simulation comprises the construction of the geometry, assigning materials and setting the solver. For no particular reason, other than curiosity, I am using CST Microwave Studio for this example.
But, We better focus on the case of the short pulse traveling in a coax with lengths that you might have at hand!.įor an easier understanding of the propagation of a pulse in a coax a simple simulation can be of good help. This is a relative issue, though: look, if the coax is >4000km in length then, even a 50Hz signal changes in time but also in space. We can also say that the short pulse changes in time and in space but the 50Hz one changes in time only. Thus, for instance, a coax is just a wire for a 50Hz signal, but a transmission line for a nanosecond-duration pulse.
They can be simply seen as a piece of wire or as a transmission line, all ultimately depending on the frequency of the signals flowing thru them.Īlthough high, the propagation speed of electric signals if finite, and in a coax with PFTE dielectric it is ~69% of speed of light. They can virtually be found on every instrumentation table in labs and yet we pretty much overlook their function. Coaxial cables are an interesting piece of the signal measurement paraphernalia.
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