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    Narrow BW (.1%) CombLine Filter

    Is it possible to design a combline filter with <.1% BW (e.g. 12 MHz BW @ 12GHz)?

    •   Alt29th June 2006, 00:06

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    Narrow BW (.1%) CombLine Filter

    Theoretically yes



    •   Alt29th June 2006, 14:43

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    Re: Narrow BW (.1%) CombLine Filter

    I think it is possable



    •   Alt17th August 2006, 03:08

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    Re: Narrow BW (.1%) CombLine Filter

    Practically, no. A filter usually has a need for a low insertion loss, flat passband, and defined in-band riple. When you take an ideal prototype and try to make it into an actual real life filter, the Q of the filter elements tends to distort the passband so much that it looks nothing like the prototype prediction.

    Now, if allyou want to do is pass a single frequency and reject out of band stuff by as much as possible, and you do not care too much about insertion loss, then yeah, you can make a narrow filter at 12 GHz. A single dielectric resonator puck losely coupled will do the job nicely.

    I suppose you could use a saphire resonator or superconductor resonator and end up with superhigh Q elements that could do the filter job, but that is more science fair than engineering.



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    Re: Narrow BW (.1%) CombLine Filter

    Temperature stability may be an issue at this narrow bandwidth. Usually a frequency conversion to a lower frequency is required prior to narrow band filtering, giving a larger relative bandwidth. For example, at 240 MHz, 12 MHz BW is 5 %.

    Quote Originally Posted by Krytar
    Is it possible to design a combline filter with <.1% BW (e.g. 12 MHz BW @ 12GHz)?



    •   Alt17th August 2006, 23:11

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  6. #6
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    Re: Narrow BW (.1%) CombLine Filter

    Thanks VSWR.

    I did design the filter, and it worked.
    My concern is its performance over temp.
    I used cold rolled steel for my resonator, and a silver plated aluminum housing.

    Unit was plugged into a sub assy after I built it so I didn't have any chance to test over temp.

    I'll build another unit to test over temp to see its performance.

    Regards
    Krytar



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