measurement of varactor - Q or ESR

To measure Q or ESR of high Q varactors at RF frequency (i.e. a few GHz to 10GHz range), coaxial resonator Boonton 34A seems to be used by some people. It does not seem to be a very common equipement to own by most.

Just wondering, if there are any other good ways besides that?

you make a resonator with components of known Q and a bias network to allow tuning of the varactor, and make a loaded Q measurement (either reflection if a one port, or transmission if a two port). Often a waveguide type resonator is used simply because the Q of everything in the resonant circuit is so much higher than the Q of the varactor, that the result is easier to deduce.

Once you have the Q, you can compute the esr, and vice versa.

You can do it a number of ways depending on your equipment availabilities. Many use network analysers. Measuring Q on a resonator is fine also.

If you want to model the varactor over a wide frequency range you want ESR. Varactors typically have a near constant Rs so as frequency gets higher the Q decreases. For most applications, knowing the Rs and the low frequency (1 MHz capacitance bridge) capacitance versus bias is accurate enough. Throw in some Cp (like 0.5 pF depending on package) if using at very high frequencies.

Thank you so much for the reply. The WG resonator has even higher Q than coax resonator. Do you know of any reference with more details for such measurement system setup?

I guess if the resonator' Q is much higher than varactor Q, then the varactor Q can be approximated by the measured loaded Q?

---------- Post added at 08:32 ---------- Previous post was at 08:29 ----------

Thank you RCinFLA! Great comments. For my case, the Q is quite high. I measured the Spar for varactor using network analyzer. However, I am afraid the diode Q is much higher than the network analyzer system's Q. So the results may not be reliable.