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Waveguide wavelenght simulation problem

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laza

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I need simulate lambda/4 transformer in the r100 waveguide (22.86mmx10.16mm) I use Agillent HFSS 5.6 or CST MWST4.3 or MWST 5.0 Dont know why depending the guide wavelenght of the B size(10.16mm) in the simulation. Very easy example: design the waveguide, the B size modified across 20mm. This dimension equal lambda/2 in 10GHz. In this case this is a bandpass filter. And the different B size solution different frequency. Please help me what is the wrong setting in the simulation.
 

laza said:
I need simulate lambda/4 transformer in the r100 waveguide (22.86mmx10.16mm) I use Agillent HFSS 5.6 or CST MWST4.3 or MWST 5.0 Dont know why depending the guide wavelenght of the B size(10.16mm) in the simulation. Very easy example: design the waveguide, the B size modified across 20mm. This dimension equal lambda/2 in 10GHz. In this case this is a bandpass filter. And the different B size solution different frequency. Please help me what is the wrong setting in the simulation.
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frankly sey, i cant undrestand your question, but the cutoff frequency of the waveguied is highly relaited to the B size.

marti
 

wavelength and guide wavelength including some physical dimension in waveguide itself are fully linearly related.

Depends of waveguide you are using but they are related linearly in most of the times.
 

The waveguide wavelenght independent of the B size in the reality. I calculated it with very old formulas, and with very easy software, but when I simulate it whit CST MWST the solution is very bad. I read the waveguide wavelenght data from the Microwave engineering handbook: 10GHz wavelengh in the freespace=30mm and in the R100 waveguide=39.7mm. The lambda/4 transformer lenght=9.925mm. The lambda/4(guide) transformer to any impedance, and another lambda/4(guide) transformer return to waveguide impedance=lambda/2(guide) lenght. I simulate it with half B size, and the solution is 9.1Ghz. Why? I know, various B or electrical size tune the resonator, but 900Mhz is very wrong data. Any else think?
 

Firstly: 9.1GHz=9100MHz (not 900 MHz), not far from 10 Ghz :)
Secondly: due to edge effects in WG-step region, the overall electrical length of transformer must be more than length in ideal case, hence, the frequency must be less than ideal, or lambda/4 transformer must be shorter.
Thirdly: when You decrease the WG B-size, You increase the contribution of edge effects (of course, the frequency more decreases in this case). Use the symmetry planes to saving the simulation time.

Best regards,
Kit-the-great
 

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