Q0 of cavity rezonator

Hello

I have Qo on cavity rezonator at frequency f1.
what is the Qo at frequency f2?
f.e. Qo=200 at 900 MHz
Qo=? at 1800 Mhz

thanks
V.

The Q is related to the ratio of volume to wall surface area. You should expect the Q to decline at the higher frequency if you just scale the dimensions.

It depends on what kind of resonator you have. Normally, metal cavity, such as combline resonator or an air coil inductor, has a higher unloaded Q at higher frequency, while dielectrics has a higher loss at higher frequency thus lower Q0.

Ok, thanks

I have in mind normally, metal cavity combline resonator.
Is there any equations on it?

thanks
V.

There are many emprical formula to calculate Q0 for combline resonator, it's difficult to say which one is more accurate as Qo is a function of ground plane spacing, skin conductivity (silve plating), frequency, impedance, resonator loading, etc. Here is a simple one:

Q0=K*b*sqrt(f)

where K is a constant approximately equal to 1600 for practical silver plated resonator, b is ground plane spacing in inches, f is frequency in GHz.

Combline filters are transmission line filters. Cavity filters are totally hollow areas enclosed by metal and have standing wave patterns. Power is coupled in and out by irises in the case of waveguides and electric or magnetic probes in the case of coaxes.