Single Bellows Cavity
Once one of the bellow had replaced the cavities in the filter setup I did some measurements of the transmitted power as a function of frequency. First I investigated how the hole diameter of the irises affects the resonaces. As the hole diameter increases the resonance are shifted toward lower frequencies. This is because a bigger hole makes the cavity effectively larger than the actual distance between the irises. The peaks are also narrower when the holes are smaller but the insertion loss is bigger. This makes sense because when the holes are smaller less power is transmitted into the cavity and a smaller spread of frequencies can resonate. Next I measured the spectrum at different lengths of the bellows. The length of the this bellows can be adjusted from 1.31 inches (full compression) to 1.65 inches. For the TM112 mode with an iris diameter of a quarter inch this corresponds to a frequency range of approximately 11.0 to 11.6 GHz. So a filter could be tuned within this range at this mode. If the filter needs to pass a frequency outside of this range a different mode would have to be used. Information on the Q of these peaks will be added to this page as soon as I can complete the analysis.