# How can I measure quality factor?

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#### mazelk

Hi

How can I measure quality factor?

Is true that:

Q = [Im | Z |] / [Re | Z |]

for pasive networks?

How is quality factor in resonating frequency?

#### xxargs

##### Full Member level 4
Re: Quality factor

mazelk said:
Hi

How can I measure quality factor?

Is true that:

Q = [Im | Z |] / [Re | Z |]

for pasive networks?

How is quality factor in resonating frequency?

for band pass filters you can try:

Q = center frequency of BP-filter / -3 dB bandwidth of BP-filter

this give loaded Q-value in system.

other methode if not can measure pass trought (S21), only
return loss (S11) ie coaxial resonator etc.

finding and adjusting to maximum return loss on resonant frequecy
(critical coupled, check in smith chart if possible) and after this, measure bandwidth of -7 dB point on return loss

and use

Q = center frequncy, maximum return loss / 7 dB bandwidth of return loss.

/xxargs

#### varactor

##### Junior Member level 2
Re: Quality factor

the most general term for calculating Q factor is

Energy stored in the cavity divided by energy dissipated per radian of oscillation

#### aboozar.hamidipoor

##### Full Member level 3
Re: Quality factor

hi mazelk:

I think yes , in fact:

as "varactor" said , we define the quality factor as : "the energy stored in the cavity divided by energy dissipated per radian of oscillation". so the definition of the quality factor depends to definition of the dissipated factor and storaged factor .
for example according to the problem boundary and problem condition if we can express the storage energy and dissipated energy in terms of the Impedance (Z) , we can define quality factor as you say : Q = [Im | Z |] / [Re | Z |]

regards.

jone1471

### jone1471

points: 2

#### eda4you

##### Full Member level 5
Re: Quality factor

jone1471

points: 2