variation L with resp to freq

In theory the value of inductance remains constant.

But practically the value L is not a constant and varies with respect to frequency.
what are the factor affecting?

Is it possible to measure the inductance and Q factor using VNA . if so pls tell me the method.

Thanks.

- Parasitic capacitance -> self resonance
- Skin effect and proximity effect

Yes, this is possible. You can measure the inductor as a 1-port (reflection) or as a 2-port (transmission).

1-port shunt: L = imag( 1 / Y11 ) / ( 2 * PI * FREQ )
2-port series: L = -imag( 1 / Y21 ) / ( 2 * PI * FREQ )

Is it possible to use the reflection coefficient S11?

How abt this method
1-port (inductor used in series with 50 ohm termination)
calculate the ZL=50*(1+s11)/(1-s11)
L=img(ZL)/(2*pi*freq)

Also how to find the Q factor using the VNA?

Sure. The only difference is that the equation is easier if you write it with Y-params.

Q = imag(Y11)/real(Y11)

You should be aware that the method is sensitive to precision error of the S-parameters, so accurate VNA calibration is required.

See my appends in The Designer's Guide Community Forum - Inductance extraction: L reduce with frequency?

Is it a new forum ?

I have used a "Inductor of value 0.010m Henry in series with 50 Ohm resistor". i measured the S11 and calculated the Q and L value as i told earlier in my post.
Is my approach correct .using a series resistor will decrease the Q value isnt?
Is there any other method?

Also i have another doubt can we use Z11 directly?

With your method, if you measure the input impedance, you have inductor and 50 ohm termination in series. To calculate the inductor Q, you must subtract the 50 ohm termination first, because that is not part of the inductor.

Surely see The Designer's Guide Community Forum - Inductance extraction: L reduce with frequency?

You should be able to understand the S11 to Z or Y conversion from the manual of your VNA, or available network analysis tutorials on the internet. Good ones are e.g. from Agilent.

Also most VNAs can display Z or Y parameters directly. The measurement accuracy depends of course on how far the value is from 50 ohm system impedance, you'll find error curcves in the instrument manual.

Hai,

I calculated the ZL from the formula ZL=Z0[(1+S11)/(1-S11)] ----------(1)

and Volker said ZL=1/Y11------------(2)
which means when i substitute the value of S11 in equ (1)
in terms of Y parameter i have to get equ (2)

But what i got was

ZL=[(1+Z0.Y22)/(Y11(1+Z0.Y22)-Z0.Y12.Y21)]

only under the condition Y12 OR Y21 equals zero i would be able to get equ (2).

In Pancho threadwhen u make port2 gnd. it will make Y12 infinite which means the entire ZL will be infinite.

Very Very Very Very Very Wrong.

It seems you can't understand difference between 1-port and 2-port measurements.
Can you understand linear circuit theory surely ?

If you do 1-port measurement, (1) is same as (2).
But (1) is not same as (2), if you do 2-port measurement.

As far as you do 2-port measurement, you can evaluate any values.

Again surely see The Designer's Guide Community Forum - Inductance extraction: L reduce with frequency?

https://www.edaboard.com/thread194988.html

Volker said "1-port shunt: L = imag( 1 / Y11 ) / ( 2 * PI * FREQ )"

This is for a 1-port measurement where the inductor is measured with the second terminal shorted.

I really sorry .
I totally got confused with 1 port and 2 port measurement.
what i am dng in my project is 1 port measurement.
so i have only y11 .
Thankyou Pancho and Volker.

Hai

I measured the S11 of 5.6n H inductor .the value of L was calculated from S11. The SRF in the datasheet is 6G Hz.
unfortunately i am getting the Resonance at 300K hz itself , and also there is more than one resonance in the circuit.

How did u connect the inductor to network analyzer ?

Do i need any circuit for connecting the inductor to the VNA?

What I did was I soldered the inductor between two connector (note: the wire length was longer than inductor size , this would definitely have an impact isnt?) ,followed by a 50 ohm termination. The connector are 50 ohm.

can u pls send me the detail about how u connected the inductor to VNA?

Long wires are bad and the 50 ohm resistor makes no sense to me.

Inductor measurement with evaluation from S11 means reflection measurement (1 port). Just use one port of the VNA, and ignore the second port.

Connect the inductor between the signal and ground of an SMA connector, a short as possible.
Then, use a second connector of the same size with a SHORT CIRCUIT and offset the phase of your VNA, so that your reference plane for the measurement is at the position where you have inserted the inductor.

However, these "homebrew" measurements as described above are not very precise. It might be more accurate to use the data from the component manufacturer.