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Torben Voigt

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Posts posted by Torben Voigt


  1. Hi @FEKOFan

    you can of course always imitate the physical real-life scenario. Means that you physically model the coaxial cables. Since this would mean some computational effort die to lots of mesh triangles, you may use a TX line in CADFEKO:

    image.png.bf662b9fe6a6ff089ec6baf425a49fc1.png

    This can be placed between two ports and will act as if a piece of cable would be present. Only that it's not a scattering object, it's rather a black box. I did't yet check the feasibility of this approach. Do you think this could be useful?

     

    Best regards,

    Torben


  2. Hi @FieldForcer,

     

    A wire is considered thin if r is roughly smaller than l/4.

    I'm not sure if I understand correctly what "loop" you are referring to. I only see a folded wire (monopole) with a differential port at one end. Again, the feed is pretty unrealistic, could it be that the one side of the port should be connected to an infinite PEC plane?

    Why do you expect the Gain to be zero in the y-direction?

    Maybe it would be easier if you could just share the design which you are trying to model?


  3. Hi @FieldForcer,

    The model is not symmetric to z=0, but it is symmetric to x=0:

    image.png.1a2399c22f9879aece2ef8f5d37232dc.png

    Wire segments should be thin. With standard mesh (segment length = lambda/12) the segments are relatively thick. Reducing the rdius would solve this.

     

    Please note, the Gain values in the 3D view are rounded by default. That's why you seem to get different results for different values of angular increment.

     

    I still think your feeding (wire port at the end of a wire) is a bit unrealistic.

     


  4. Hi @FieldForcer,

     

    The far field request in the second picture sems to have much larger increment than the one in the first picture, although you write "finer spacing". I would recommend trying an increment of 1 degree or 0.5 degree.

    Loking at the antenna without the reflector, the main beam is oriented in the negative y direction:

    image.thumb.png.907d3ec7c0e6ba93f9b31c344fd16e1e.png

    Therefor I would either put the reflector in the negative y-direction or rotate the antenna so that the main beam is in the negative z-drection (where the reflector is now).

    Since your far field request is defined as half space, I assume that you want the main beam of the complete model (antenna + reflector) to be in the positive z-direction, correct?=

     

    -> If you still have questions, I would ask you to precisely describe what exactly you're trying to achieve with this model.


  5. Hi @FieldForcer,

     

    You defined a voltage source on a wire port at the end of a wire. Normally wire ports are definded either along wires or on connecting points between wires and a metal faces. Defining a wire port on an open end of a wire will probably not result in what you expect. You may for example connect the open end of the port to a metal face like this:

     

    image.png.d1a7bb4efe9794b13f973c366ced1329.png

    I also saw that you defined a variable "lambda" with c0/freq. Your global unit is set to mm, so you will have to define "lambda" like co/freq*1000.

     

    Still, the pattern of this radiating wire is oriented in the y-direction, so I wonder if you did something wrong?


  6. Hi @pmcardle,

     

    please excuse the delay in answering. I now had a look at your model, but I'm still not sure I fully understand. You defined an air region (FEM) around the anisotropic body to make it infinite in x and y, correct?

    1. An air region will not extend the anisotropic region, it just adds air.
    2. The air regions is defined only 0.01 µm thicker than the aisotropic region, which results in obvious meshing problems:
      image.png.409164419745113aeeda189c4048e3eb.png

    Presently I don't see a way to simulate infinite anisotropic layers. I would put a large air box around and solve everything with FEM, see PEC_alt.cfx


  7. Hi @shan25,

     

    The feedback from the developmet:

    This is the expected behaviour, as for UTD the effect of coatings is only taken into effect for the reflected rays (there are no transmitted rays here for a PEC plate backed with a coating, but even for a transparent TDS sheet there are no direct rays in the current UTD formulation - this is well documented and also I believe the Feko solver will give a warning).

    In the shadow region, the only contributions to the fields are edge and corner diffracted rays, and for these, always the PEC formulas are used, i.e. if you add a coating to the plate or not will indeed not have any impact on the field in the shadow region, and also in fact not in the region where there is no reflected ray, only the incident rays (i.e. between the ISB - incident shadow bounday - and RSB - reflection shadow boundary).


  8. Hi @MOHAMED HAMDALLA,

     

    The difference can be explained by the differet methods. While the MoM (crosstalk2.cfx) takes into account all possible effects in the scenario,  the Multi Transmission Line Theory (crosstalk_alt.cfx) is obviously an approximation. The MTL is extremely useful for complex cable harness, possibly different kinds of shielding included, complex cable bundles in an electrically large environment (e.g. car), etc.

     

    S-parameters for cable ports in FEKO are not yet supported, but planned for 2019. For simple scenarios like this, I would recommend using MoM, where you can use an SParameterConfiguration to get S21 directly.

     

    One question about the picture in your last post: The frequency is given in Hz, is that correct?


  9. Hi Mohamed,

     

    For multiple cable instances within one CableHarness only capacitive / inductive coupling effects will be taken into account. It cables have a certain distance these effects will be zero and and only coupling via field strength will be present. To take into account coupling due to radiation, the cables must be in seperate CableHarnesses, see attached crosstalk_alt.cfx

     

    Here's the comparison between wires and cables:
    image.thumb.png.bf3ed1a7f6403ace828b4fe6bd61a656.png

    image.png


  10. Hi Keshab,

     

    In the ExampleGuide.pdf (default C:\Program Files\Altair\2018\help\feko\pdf\) you should find several examples to show the different port types in FEKO (for MoM: wire port, edge port, microstrip port). Feel free to add the model here.

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