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  1. #1
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    Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

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    Hi,

    As shown above,

    there is always a shunt inductor in SMD (Surface Mount Device) antenna design.

    I know it's for tuning.

    Nevertheless, why is inductor always used here?

    Capacitor is rarely seen here.



    What key words should I google to understand the detailed explanation?

    Thanks a lot~!!

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  2. #2
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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by criterion456 View Post
    there is always a shunt inductor in SMD (Surface Mount Device) antenna design.
    Not in the place where you have drawn it.
    There is often a series inductor, to "extend" an antenna that is physically too short. Often combined with a shunt C.

    Here's an article from 1953 on matching short antennas: http://www.rfcafe.com/references/qst...ember-1953.htm


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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by volker@muehlhaus View Post
    Not in the place where you have drawn it.
    There is often a series inductor, to "extend" an antenna that is physically too short. Often combined with a shunt C.

    Here's an article from 1953 on matching short antennas: http://www.rfcafe.com/references/qst...ember-1953.htm


    Sorry, perhaps my previous photo didn't expound my question well.


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    The two photos are from datasheet.

    As shown above, C1 is just the shunt component, and which is always implemented as an inductor.

    Other datasheets almost adopt the identical design.

    I'm wondering that why is the component always inductor.


    Thanks a lot~!!


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  4. #4
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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by criterion456 View Post
    As shown above, C1 is just the shunt component, and which is always implemented as an inductor.
    That's unusual for the electrically small antennas that I know (or have designed myself). Can you link to the antenna datasheet?


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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by volker@muehlhaus View Post
    That's unusual for the electrically small antennas that I know (or have designed myself). Can you link to the antenna datasheet?
    Sorry for the late reply.


    https://gofile.io/?c=IqWDQx

    Antenova, plz see page 15

    Pulse, plz see page 7



    Thanks~!!



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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    This come from the theory. Small (or short) antennas are capacitive.
    So, for impedance matching they need an inductor (or more inductors) to "tune out" this capacitance.


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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by vfone View Post
    This come from the theory. Small (or short) antennas are capacitive.
    So, for impedance matching they need an inductor (or more inductors) to "tune out" this capacitance.
    That was my explanation in #2. But they have a shunt L, not a series L. We don't know what the internal design looks like, so I have no idea what they use this shunt L for. There is a tap with some shunt inductance to ground for PIFA-type designs, but I don't know if that applies here.


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  8. #8
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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Yes, series inductor is more convenient, but the matching can be done with almost any configuration.
    These chip antennas have awful internal impedance which require unusual matching typologies.



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    Re: Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

    Quote Originally Posted by vfone View Post
    Yes, series inductor is more convenient, but the matching can be done with almost any configuration.
    These chip antennas have awful internal impedance which require unusual matching typologies.
    vfone, volker@muehlhaus

    Thanks for your reply.

    I think perhaps this design is due to the impedance of the antenna itself.



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