Continue to Site

# Finding Measured Q-factor and Resonance Frequency of CPW Line resonator

Status
Not open for further replies.

#### sandbo

##### Newbie level 6
Hi,

I am simulating to find the resonance frequency and measured quality factor of some CPW transmission line resonator with a short circuit as termination.
They are coupled to the feedline via a series coupling capacitor.
I set the length from the coupling cap to the short-to-GND, then I applied a sheet and set the boundary as lumped RLC to model the coupling capacitor.
Then I create only 1 port to the feedline as a single port, reflective measurement.

I was able to simulate and plot the results as mag(S-parameter), and also mag(Zin),
however I am not sure how I should interpret the results for the resonance frequency and q factor.

From the S-parameter plot, I can see only 1 dip happening around the expected resonance frequency, but how I should extract the Q-factor?
The current way I used is to find the lowest mag(S_resonance), then find the frequency such that mag(S-parameter) = 0.707*mag(S_resonance), then take the reciprocal of the fractional bandwidth.

From the Z-parameter plot, I can see first a shallow dip, then a sharp peak with the frequency sweep. The dip corresponds to the S-parameter dip, however the peak is not shown in the S-parameter plot. In this case should I consider the dip, or the peak as resonance frequency?
The way I understood was to consider the lowest point of mag(Zin) (assuming it is a series RLC resonator), then find the frequency such that mag(Zin) = min_mag(Zin)/0.707

The above were my understanding over Pozar's method from his book Microwave Engineering, but I guess I was confused over some concept, appreciated much if you can help with explaining them, thanks.

Status
Not open for further replies.