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  1. #1
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    what is the best substrate for a microstrip power divider ?

    hello!

    i made a braodband ( 1-3 Ghz) wilkinson power divider with FRF4 substrate and it works very well.
    but when i try to make another one (2Ghz - 18Ghz) with FRF4 Er = 4.5 or Duroid Er= 2.57 i've got problem with S21 parameters .
    between 6Ghz and 18Ghz i've got a S21 who decrease between -8dB an -30 dB?

    can somebody tell me why? it's the substrate is the cause of my problem
    which topology is the best ? straight lines or curves?

    thanks a lot

    PS: don't care of my english i'm a beginner

    •   Alt12th January 2005, 19:44

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    Re: what is the best substrate for a microstrip power divide

    Definitely the reason of poor S21 at those frequencies is the FR4 material.
    For higher frequencies you can use one of these materials from Rogers:
    http://www.rogerscorporation.com/mwu/pdf/prodselect.pdf
    Curves lines usually are used in broadband splitters to minimize the total physical length.



    •   Alt12th January 2005, 20:41

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    Re: what is the best substrate for a microstrip power divide

    thanks vfone for your explanation.

    i use curves lines but it's difficult to join them together and respect the λ/4

    another question more.

    can you have explanation about the relation between frequecies and substrate?
    for example which substrate you'll use for a divider at f0= 5Ghz?



    •   Alt12th January 2005, 21:13

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    Re: what is the best substrate for a microstrip power divide

    The loss tangent of the material is frequency dependant
    Here you can find formulas for Er and Dielectric Losses:
    http://qucs.sourceforge.net/tech/node31.html



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    Re: what is the best substrate for a microstrip power divide

    a good material at high freq is RT 5880 or materials from Taconic like RF-35. RT 5880 has low tand=0.00019 n is very stable at high freq works very well in Ku band.



    •   Alt13th January 2005, 00:46

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    what is the best substrate for a microstrip power divider ?

    it is not only the loss tangent. there are more effects associated to the substrate material which are important at high frequencies: surface waves, which are generated by leakage and are linked to the substrate thickness and epsilon.

    I suppose you use SMA connectors soldered to the MIC traces. These connections are also important.

    You also mention that it is a wilkinson splitter: do you know the parasitics of the resistor?

    regards



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    Re: what is the best substrate for a microstrip power divide

    hello!




    to answer to dowjones: i use cms resitors but i don't know their parasitics .

    i use SMA connector soldered to the µstrip.

    thanks



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