[moved] Reconfigurable antenna isolating the bias from the RF signal?

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raju081006

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I am working on a pattern reconfigurable antenna and for this i need to bias the PIN diode from a battery through bias line. For this I need a RF choke inductance to isolate the ac from the bias line. I have seen different value of inductor is being used by different author. Is there any specific formula to select the RF choke to select for frequnecy band of 1.8 to 3 GHZ?
 

Re: Reconfigurable antenna isolating the bias from the RF signal?

The value is up to you. Just select an inductor with a SRF above 3GHz with the largest XL as you can find.
 

Re: Reconfigurable antenna isolating the bias from the RF signal?

thank you for your answer? you mean self resonant frequency of the inductor? why the srf above 3 GHz which is my upper limit of my antenna? I was searching for a reference while selecting the inductor? can you please suggest me a reference?
 

Yes, I mean the SRF of the inductor. Above the SRF, the "coil" acts like a capacitor. Coil Craft has a line of conical inductors with high SRFs that might work for you.
 

Inductor specification?

I need to buy very small size inductor which srf is above 3.2 GHz. When I buy a certain model of inductor, is the SRF mentioned in the datasheet of that inductor or I should measure it later after buying the inductor chip?
 

The basic rule is that the reactance XL of the choke should be at least x10 greater than the circuit impedance.
For example if the circuit impedance is 50 ohms the XL of the choke should be greater than 500 ohms.
XL cannot be larger as possible, due to increasing of its DC resistance, which most of the circuits don't accept.
 

wow, just looking over the coilcraft site, and there have been some recent improvements in SRF for chip inductors.
For instance, it looks like you can get a 34 nH inductor with a 4.45 GHz SRF.
https://www.coilcraft.com/0302cs.cfm

I would use that. That would be j384 ohms at 1.8 GHz, which should be good enough for a bias network.
 

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