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Help needed with Interdigital filter

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PaulHolland

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I have designed an interdigital filter with PARFIL program, the results look perfect in the PARFIL program but when I export the dxf and import it in @ds or MWO I get completely different results. The filter is off frequency and the performance is terrible. Any clue what is going wrong ???..

I need a bandpass filter for 4.4 - 5 GHz (0.5 dB points) 5th order.

Paul.
 

cybq

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Why not design it derectly within @DS / MWoffice?
 

Kit-the-great

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Did You correctly define the metal case around filter ? It is very important for this filter type. I don't know what analysis method use PARFIL to simulate the filter, but if it is a sort of circuit analysis (not EM-simulation), as I suppose - You can give not accurate results with PARFIL, due to this simulation method can't correctly allows the coupled lines effects. You can correctly simulate this filters only using the EM-simulation algorithms.

Best regards,
Kit-the-great
 

pinguin

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Do you have too thick lines? Coupling effects in EM simulator of MWOffice are calculated accurately for thin lines. Thickness parameter is only for conductor loss calculation.
 

Spasomat

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As kid-the-great said I also experienced problems in a circuit simulation of a hairpin-filter. The circuit-simulator did only cover the coupling of two coupled lines at a time. The coupling to the other coupled lines were the reason my simulation did not fit with the measured results.
Finally I oprtimized the filter with a 3d-solver but it was pretty time-consuming. If someone knows a solution for a faster optimzation procedure with filters in 3d-solver´s he is invited to tell us.

Best Regards,

Spasomat
 

Kit-the-great

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The circuit-simulator did only cover the coupling of two coupled lines at a time. The coupling to the other coupled lines were the reason my simulation did not fit with the measured results.

I think, it's only a part of problem. In MWO the models of more-than-two coupled lines presented, but... I think the problem also in complex frequency dependence of coupling factor in real filter. The most fast technique of filter simulation, as I know, is modal analysis. This method released for waveguide filters in a few programs, such as Wasp-Net and uWaveWizard, but I never seen the programs, that applied this technique to interdigital microstrip filters. I'm suppose that this method as applied to interdigital filter analysis can increase the simulation speed very much, but it's not a simple problem !

Best regards,
Kit-the-great
 

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