RF choke + Inductor Self Resonant Frequency

[spid3rx]

Hi,

Just would like to know if I would want to choke a line that operates in 2.4GHz environment, what is the guideline to select the right components?

I had prepare series pad for the line and am thinking to put the inductor as the choke.
I should be using inductor choke with SRF at 2.4GHz or above or below the inductor SRF??

Please advise.

thanks,

 

[tony_lth]

You can using AppCAD to calculate the inductor value. Or just use thumb of rule to decide ZL.
Although the SRF of inductor maybe several hundreds MHz, but I used it as RF choke even to 6G, and it works. Higher freq, smaller package. Coil is better.

 

[eee100]

Hi,

SRF should be higher than the operating frequency. The higher the better. As the operating frequency comes closer to SRF the effectiveness of the inductor decreases. If SRF is below the operating frequency for an RF choke, the parasitic capacitance would cause oscillation.

 

[tony_lth]

Hi,

The following is link to one famous inductor vendor:**broken link removed**

You can see the max SRF is only 2G, but this post will work on 2.4G, so how to solve?

If SRF can't be higher than working freq, maybe should much lower than working freq. I have use normal coil inductor to mass volume production, Never found oscillation caused by inductor. Such as used 39nH/0603 for 4G RF choke.

 

[eee100]

For example Murata produces inductors with SRF values of up to 6GHz...

 

[David.D]

SRF should be a little higher than the operating frequency.

Added after 45 minutes:

SRF is defined by the equation: SFR=1/(2*Sqrt(L*C))

For choke applications, the SRF is the frequency that provides the best signal blocking. At frequencies below the SRF, impedance increases with frequency. At the SRF, impedance is at its maximum. At frequencies above the SRF, impedance decreases with frequency.

In general, the choice of inductance value typically determines the SRF and vice versa. The higher the inductance value, the lower the SRF, due to increased winding capacitance.

Inductance and impedance rise sharply near an inductor’s self resonant frequency (SRF). For choking applications, chose an inductor whose SRF is at or near the frequency to be attenuated. For other applications, the SRF should be at least 10 times higher than the operating frequency.

 

[spid3rx]

Thanks for all the input.

David D.
Really appreciate the diagram. Makes me understand better. I tried a couple of inductors
I am using the inductor value with the SRF at around 2.4GHz.
I found that the SRF of 2.4GHz and 2.5GHz is the best for choke purposes. It cause less
effect to the antenna nearby.

should it be recommended to use those that the SRF slightly higher than the operating
frequency? like 2.5GHz for instance ?

thanks