Hello all,
It is a while I am struggling with a problem in my simulation. Since nobody could find anything wrong in simulation, so I thought maybe something is wrong in the software or I do not know about some special adjustment that I should do in the CST.
Anyway, I designed a back to back microstrip to SIW transition. It works fine, the results are ok (S11 < -10dB) in all bandwidth when I am using the waveguide ports for excitation. But when I use Coaxial cable to excite the transition suddenly S11 goes to 0. The dimensions of the coaxial cable are from
Anyway, I designed a back to back microstrip to SIW transition. It works fine, the results are ok (S11 < -10dB) in all bandwidth when I am using the waveguide ports for excitation. But when I use Coaxial cable to excite the transition suddenly S11 goes to 0. The dimensions of the coaxial cable are from south-west Microwave company (K connector) and connection between the coaxial and microstrip is correct. So I was wondering is anybody have any idea that why it is happening ?
I also have the same problem when I put a waveguide port in one side instead of having back to back transition !!
I will appreciate any idea
Sara,
This is the almost the same problem that I also faced. But my problem was like the impedance was varying like form about 0 to almost 10k ohms (specially at higher frequency) . I would like to know that did you face the same problem ? Also I managed to sort out this by using CPW and also by changing the dimensions of the port. Please let me know that does this helped?
Regards,
Anand
Thank you for your reply Anand,
Actually, I do not have a mismatch problem, Connector is a 50 ohm one and microstrip is 50 ohm as well. the frequency that I am looking at is between 22 to 28 GHz
Did you faced any problem like impedance varying to like about 10k or so?
hi dear sara. i have simulated many siw structures. specially phase shifter and power dividers. i use tapered transition between microstrip and siw. my frequency range are 26-40 GHz. you can send your cst file to me. i am familiar with cst not by hfss.
Hi all,
If Iam not wrong, you have to deal with two transitions. The first one, microstrip to SIW transition was ok, your results are (S11 < -10dB). In the entire one, coaxial to SIW transition , you don't get the expected resuts.
But, How about the coaxial to microstrip transition ?
It would be easier if you share a picture of your design.
Thanks.
Thanks for all replies,
For clarification, I added 2 photos of the transition.
As you can see in the picture the transition is fine but as while as I connect the coaxial connector instead of waveguide port everything goes wrong and S11 is almost 0.
Hi Sara, Hi all contributors
Sara, I suggest you to design and simulate the back to back coaxial to microstrip transition. Maybe there is something wrong here.
Hi,
1) The suggestion of Djilali Hammou is a good one: you can see if you have a problem with connectors.
2) I am a little bit surprise by your excitation (see on your picture) port when you use your coaxial waveguide. hewer, I don't know CST: I used EmPro with connectors and I have no problem in my simulations
3) If you want, send me your design. I think I can export from CST to EmPro since I have a research assistant who is expert with CST.
Microwave! Science with sometimes a huge loss of time because you have just forget a very small detail... but a very nice science...
François
Hi,
Please see attached file. An SMA connector is designed using CST. (The designed SMA connector is not proper at high frequencies.)
Please note that exciting by the waveguide port is for number of modes only and the CST shows the results of each mode separately.
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