Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

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

Status
Not open for further replies.

criterion456

Member level 2
Joined
Sep 13, 2015
Messages
50
Helped
6
Reputation
12
Reaction score
6
Trophy points
1,298
Activity points
2,022
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~!!
 

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



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~!!
 
  • Like
Reactions: Anomis

    Anomis

    Points: 2
    Helpful Answer Positive Rating
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?
 
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.
 
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.
 
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.
 

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.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top