Error CST: The calculation seems to be unstable! A possible source of instability....

leesixan · Sep 12, 2012

I have problem with CST 2010. I met error: "The calculation seems to be unstable! A possible source of instability could be given by inaccurate definition of internal waveguide ports. Please consider to increase the dimension or shield your waveguide port"-attach file

. I search Google and this forum, but i dont find solution.
What's the reason for this?
please help me if you know
Thanks for read thread.

bubuta77 · Sep 13, 2012

Can you be a little more specific about your project? What are you simulating? If it planar (microstrip for example) the rules for defining size of waveguide port exist (depend on substrate height & microstrip width). Additonally for planar projects i usually simulate SMA connectors to connect to lines (after it i added waveguide port to SMA - solves to me all problems with definition of size)

leesixan · Sep 13, 2012

bubuta77 said:
Can you be a little more specific about your project? What are you simulating? If it planar (microstrip for example) the rules for defining size of waveguide port exist (depend on substrate height & microstrip width). Additonally for planar projects i usually simulate SMA connectors to connect to lines (after it i added waveguide port to SMA - solves to me all problems with definition of size)

I am simulating CPW+CLRH_TL. My Design in attach file. I hope it useful.View attachment zor antenna.zip
Thanks for reply my topic.

bubuta77 · Sep 14, 2012

Your port seems to more too large - it touches three or two different lines. I'll see it more thoroughly when i'll have more free time. For a while look at attached pictures it can help you. My advice build SMA connector (it takes time) or use discrete port

leesixan · Sep 15, 2012

bubuta77 said:
Your port seems to more too large - it touches three or two different lines. I'll see it more thoroughly when i'll have more free time. For a while look at attached pictures it can help you. My advice build SMA connector (it takes time) or use discrete port

I think my port is large, too. But if this dimension is smaller => error come faster. I'm begineer. Have u any sample built by CST?

bubuta77 · Sep 20, 2012

Sorry for late response. Attached example project with SMA connector

leesixan · Sep 20, 2012

bubuta77 said:
Sorry for late response. Attached example project with SMA connector

Yes. It's GND. But i don't understand why not good? I set port like a tutorial of CST and HFSS (attach file).
I can't open your file. Have error

. I'm using CST 2010. And you?
Thanks you very much for your help.

bubuta77 · Sep 20, 2012

I use 2011 ((
Additional question (i don't understand antennas, but it seems to me that your feeding line is not connected to other parts of antenna, is it suppose to be that way?)
About the port may be you are right but logically doesn't seems to me. Anyway try SMA connector you have nothing to loose. I can do it but it will take for me month to do it (unfortunately i haven't much time at all) so if you want just tell me..

leesixan · Sep 21, 2012

bubuta77 said:
I use 2011 ((
Additional question (i don't understand antennas, but it seems to me that your feeding line is not connected to other parts of antenna, is it suppose to be that way?)
About the port may be you are right but logically doesn't seems to me. Anyway try SMA connector you have nothing to loose. I can do it but it will take for me month to do it (unfortunately i haven't much time at all) so if you want just tell me..

i will try sma connector. But i can't open your example and i dont have datasheet of sma connector to simulation. I want to do it my self. After 1 week, if i can't do it, please help me

leesixan · Oct 2, 2012

bubuta77 said:
I use 2011 ((
Additional question (i don't understand antennas, but it seems to me that your feeding line is not connected to other parts of antenna, is it suppose to be that way?)
About the port may be you are right but logically doesn't seems to me. Anyway try SMA connector you have nothing to loose. I can do it but it will take for me month to do it (unfortunately i haven't much time at all) so if you want just tell me..

I dont know dimension of sma connector. Then i choose random . I dont know my design is true or wrong . Can u check it for me? Thanks so much for your help

bubuta77 · Oct 2, 2012

I'll check it but unfortunately you must be patient cause it will take time for me.
SMA dimensions: I usually use AppCad/Passive components/Round Coax for calculating dimensions - Zo of connector is 50ohm)). Dielectric and dimensions can be different from real life connector, more important for me characteristic impedance.
I design dimension depending on my substrate: external metal of connector(its ground) must have the same -Z coordinate (at minimum) as ground.

chinwi85 · Dec 11, 2013

In order to calculate the maximal stable timestep, MWS uses a certain method. This will
give you a stable timestep in 99.9% of all cases. In some cases it fails to give you the
correct timestep. In this cases you have to reduce the timestep till the calculation get
stable. I would start with a factor of 0.9, if it still is unstable go to 0.8 and so on.
http://www.cst-korea.co.kr/Application/CST_MWS.pdf

amntt · Dec 18, 2013

chinwi85 said:
In order to calculate the maximal stable timestep, MWS uses a certain method. This will
give you a stable timestep in 99.9% of all cases. In some cases it fails to give you the
correct timestep. In this cases you have to reduce the timestep till the calculation get
stable. I would start with a factor of 0.9, if it still is unstable go to 0.8 and so on.
http://www.cst-korea.co.kr/Application/CST_MWS.pdf

how many time we have permission to do this? for example until 0.5 or 0.4 ?

Diponkar · Apr 11, 2014

i also sometimes faced same problem.but this has been solved when i increase the dimension. But why i don't know? Could you please why this problem i faced and why it is being solved after increasing the dimension?

I have another problem regarding antenna design by CST. I can't add inclined slot on patch since i don't know how to add this. I can add straight slot. And what is the appropriate method to excite feed line by discrete port and waveguide port?

Error CST: The calculation seems to be unstable! A possible source of instability....

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