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[SOLVED] Why is there always a shunt inductor for SMD (Surface Mount Device) antenna?

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criterion456

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ANTT.png

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~!!
 

volker@muehlhaus said:
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: https://www.rfcafe.com/references/qst/short-antennas-mobile-operation-qst-september-1953.htm
Click to expand...



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


ANTTT.jpg
ANTTT_2.jpg


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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criterion456 said:
As shown above, C1 is just the shunt component, and which is always implemented as an inductor.
Click to expand...

That's unusual for the electrically small antennas that I know (or have designed myself). Can you link to the antenna datasheet?
 
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.
 
vfone said:
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.
Click to expand...

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.
 
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 said:
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.
Click to expand...

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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