archimedean spiral cst 2008

I'm designing the archimedean spiral antenna (single-arm) (microstrip type) and I have trouble with simulating this antenna using CST. I don know how to choose the excite port for this antenna. My model does not contain the ground layer because I want to see the operation of this antenna without ground effect first.
Could anyone help me!
Thanks a lot!

You can try antenna magus. There is an example of archimedean spiral. You can export it into CST2009.

Thanks for your reply. But i'm using CST 2007, does it support antenna magus?
I've tried to use waveguide port (my model doesn't contain ground so I set the boundary condition all to open (add space), is it ok? May it not because the results i get are different from those in a paper.

Antenna magus is not support CST2007 even CST2008. Actually I don't have experience in simulating archimedean spiral using CST. But using antenna magus I think it can help you so that you can make the feeding technique easily.

Thanks for your reply. The antenna in Antennamagus is archimedean two-arm. The feeding method of this is deffferent from the single-arm type. I posted here my model.
In this model i used the waveguide port (simulating coaxial) but the result is not good.
Could anyone help me.

And here is another method i ve tried to simulating this antenna. I used the waveguide port at the edge of the spiral but it get errors "the waveguide port is too small....". Please help me.
Thanks

What is the frequency range of your antenna? I'll try to simulate it using CST Microstripes and I give the results.

According to the theory, the inner (7.9 mm in the model) and outer radius (29 mm) determine the lower (6Ghz) and upper freq (13Ghz) of the antenna. In CST, I've set the freq range to 0-16Ghz.
My problem is how to set the excited port to simulate in CST. In the first file I posted, I tried to simulate the coaxial but the results are not good; in the second
I set the waveguide port at the edge of the spiral (as in the paper but they use HFSS) however i get error "the waveguide port is too short...). I dont know why.
Thanks in advance.

This is the S parameter that I get from CST Microstipes. The feeding is using coax port. In simulating antenna using a coax port you should make inner core, dielectric, and outer conductor. 3D model that I get from you only have inner core I think.

Hi freqzt,
Thanks for your reply. Now I have some questions:
1. Did u use my model to simulate (with all the dimensions as in the model).
2. What is the dimension of the coaxial u used (inner, outer, material of the dielectric...). In the model I had the dielectric of the coaxial but its material is the same as the substrate and they are added together in CST. As u said, I have to construct the outer conductor, I will try it.
3. What do u mean CST Microstipes. does it belong to the CST family?
Anyway thanks u so much.

1. I use your model with all the dimensions.
2. The dimension of coax:
inner: 0.93205 mm
outer: 3.175 mm
εr dielectric: 2.16
it makes the impedance is 50 ohm.
3. CST Microstripes is the new family of CST. You can check it here.

I hope it can help you.

Hi freqzt,
I ve tried your suggestions but the results still not same as in the paper and your result (s11) too. Could u send me the farfield results (at 10G) u got in CST Microstrip. There maybe an impedance mismatch between the 50 ohm coaxial and the antenna. But I think this affects only the return loss not the far field result.
Thanks so much.

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