Rectangular to ridge waveguide transformer

Hello,
does anybody have experience with this type of transformer?
I have normal rectangular waveguide and a ridge waveguide, I know their impedances (from CST MWS simulation)
and I wanted to use regular quarter wave transformer, I calculated it's impedance and set its length to be one quarter of the wavelength (wavelength on the transformer step). But my |S11| was only -10 dB.
Can anybody help me?

Thanks.

I wonder what's a "regular quarter wave transformer" between ridge and rectangular waveguide? What's it's cross section? I presume you are usig H10 mode?

Main reason that Ridge Waveguide was invented is to make it wideband compared to the standard Rectangular Waveguide which is narrow band due to cut-off frequency.
If you want to keep the wideband system I don't think you can use a quarter-wave transformer, which is narrowband.

Thanks for answer,

This is my geometry, on the right, there is a ridge waveguide with very thin ridge, on the right is a rectangular waveguide and I the section inbetween is supposed to be my quarter wave transformer.
Yes, I'm using H10 mode

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Yes, I know, but I'm not using ridge to increase my bandwidth, it will be part of a septum polarizer, so narrowband is good for me

Instead of using a precalculated ridge height for the lambda/4 transformer, did you try to optimize it for S11? You might also give it a wedge form and vary the length.

due to the pretty different field structures in ridge vs rectangular, you will have evanescent modes that will cause an apparent reactance that will limit your bandwidth possible. You might do better with a linear taper of the ridge.