how to find the q of a inductor
jgkoh78 said:
How do i go about calculating the Q valvue of the MN?
Ok... you want Q on whole system, not simple inductanse or capacitance measure on single item, and this make problems litte bit worse (why not describe whole problems from beginning ???)
I not look on this so much yet, but remeber loaded Q is always depend of connected impedance (50 Ohm in your case) and resistive impedance backward in circurits (RL) and all Xl and Xc storing of energy.
You cannot calculate Q in system from only component L and C inside rectangle MN, you must calculate with Cl, Rl and Rs to make system Q from port side view. If you shift Rs or Rl, you measure different system Q.
You using ideal L in MN rectangle, but i reallity you never find perfect L and this componet have Q around 300 in best case and in range < 1 nH Q-value is often very poor. - ie 'L' should modelled L and serial R or as lossy component
Possible one methode to measure from outside port (from your generator side) is using methode describe:
www.trans-techinc.com/appnotesPDFs/No1015.pdf
(complex load as 25 Ohm + (-)j25 Ohm give reflection coefficient Γ=0.4472, VSWR=2.618, and 6.99 dB return loss - so 7 dB return loss (or VSWR=2.616:1) point measure from middle of good match seems correct methode to hunting 3dB bandwidth (and half power) point inside network via method of measuring return loss (S11).)
I put up your schematic in linear simulator (vipec), in S11 measure and find critic coupled impedance 50 Ohm (ie fairly matched) as 1.509 GHz and measure frequency on -7 dB points in S11 both side as 1.509 GHz => 1.417 GHz and 1.597 GHz ( I try L with Q=150 with very little difference)
And I using formula:
Code:
f0 1.509 Ghz 1.509 Ghz
Q = -------------- = ------------------ = -------------- = 8.38
Fhigh - Flow 1.597 - 1.417 0.180 GHz
your Q-value in network is ~ 8.4
(this methode is useful to measure on physical unit with VNA if not possible to measure transfering power (S21).
Other possible intresting page from Agilent is:
**broken link removed**
Your schematic is very simular to crystal model and crystal measure (also agilent) down on page:
http://www.home.agilent.com/agilent/facet.jspx?c=153424.i.2&to=80030.k.1&cc=US&lc=eng&sm=g&no=25
And possible using formula from page (after reorder) to calculate directly from component value and not as indirect methode (via measure) as above methode.
(I not checked this)
/Xxargs