Coax to waveguide transition in CST 2009

Hi to all:

I'am trying to simulate a simple CtW transition but is impossible tio have a value of s11 minor than -0.06.

What is the error?

hai try to design the connector with spacer like teflon. it should between the centre conductor and the outer ring. centre conductor radius- 0.65 mm and spacer radius(teflon)- 2 to 0.65 mm(outer and inner) and outer rind radius 2.2 to 2 mm (outer and inner) and hieght of the conductor above the wave guide is minimum 5 mm.

Appart from this u have to insert a cylinder in the end of the centre conductor for matching u have to optimize the radius and height it should be inside the waveguide.

Hi,

yes, of course. You are simulate transition and antenna, not only transition. Can you tell me, what the energy will be do after get to the waveguide from coax? Go to the end of waveguide and there is free space - antenna. Do you see it? So on the end of waveguide must be port too.

But the best will be, if open help a try search: "Coax To Waveguide Transition" - there is example. After set port and boundary correctly.

PS:
Why? He can use air coax. It is OK.

See in the help, and try redraw it. Will be better, if you draw waveguide as vacuum cube and set correctly boundary. And the port on the coax: set it over whole coax.

and you can use PEC, (perfect conudcter) - for calculate will be better and the you can tell, that aluminum ≈ PEC

another tip: change frequency range to 1.5 - 3 GHz, for example, you will see better the peak. And try set Pmn about -18. The Pm not will be about lam/4, but about lam/8. And after you must tune up Pmn and Lm. (for example: Pmn -18 and Lm decrease about -4)

see at the attachment, is it better?

TXS!

Only covering all the port and expanding the frequency range now I have some values with a sense.

I'm continuing proving a coax to waveguide with a horn (still with classics!)

In a couple of days probably I'll return with more questions.

thanks a lot again!

Hi again:

I've accopled a horn to the wg and tryied to optimize playing with monopole long and position and this is the best that I could obtain. I've calculated the horn with the formulaes from C. A. Balanis - Antenna Theory - Analysis and Design - 2° Ed. (Wiley, 1997) and the attached very simple spreadsheet.

2 questions:

- What parameter can optimize for decrease S1,1?
- The radiation and total efficiency what express exactly? ie: in this example what value would have for a 100% of eficiency?

PD1) The simulation is compressed with 7-zip.org
PD2) excusme for my (very) bad english

1) if you read C. A. Balanis - I think, that you can find the answer. Try change the dimensions in CST. Optimize horn without coax to waveguide transition.

2) in this case: efficiency is about S11. Return loss between horn (waveguide) and free space.

Hi
find the attachment.

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