Modified Reference Cavity Measurements at CERN

The signal was excited using a weakly coupled probe and measured from the output feedthroughs. We only had one spacer and we put this on feedthrough 2. The spacings between the end of the feedthrough and the wall of the reentrant part of the cavity were therefore:

Port 1 of the VNA was connected to the antenna while port 2 was connected to feedthrough 1. Feedthrough 2 was terminated with a matched load (left) and short circuited (right).

Port 2 was connected to feedthrough 2. Feedthrough 1 was terminated (left) and short circuited (right).

The measured quality factors were:

Feedthrough	QL	QL+short
1	76	116
2	73	214