CTF3 Cavity Pick-up to Waveguide Spacing

Cross Coupling

The separation between the pick-up in port number 2 and the wall of the waveguide was varied. The curve for separation of 0.2mm looks anomalous. This may be because the cavity was dismantled and reconstructed between this measurement and all the others.

Reflection and Transmission

This time, the separation between all pick-ups and the waveguide walls were varied simultaneously.

The peak reflection amplitudes seem to vary non-linearly where as the peak transmission amplitudes vary linearly.

There is also variation in the resonant frequency of several MHz.

The loaded Q was measured at each separation using the transmission curves between opposite ports and exponential curves were fitted to the results. The limits of these curves are printed on the graph and give values for the internal Q.

Measurements at Finer Spacing

0.30-0.40mm

There is a clear change in the S-parameters as seen before

The frequency seems to be constant

0.15-0.25mm

As expected, the change in the reflection parameters is clearer at smaller separation.

This time, the resonant frequency seems to change.

Perhaps a narrower frequency range is needed. First, look at the results of simulation.