Shawyer Cavity Simulation Optimizations

I will be back up at the University next week after the holiday Monday but just for a few days as I won’t be around on Thursday or Friday next week.)

This week a cavity (see the attached picture) was simulated and optimized to generate a pure TE0,1 mode and it turns out the diameter of the small end of the cavity was very important as even a difference of 1mm would mean a different mode. The mode was less sensitive to the length of the cavity as a change of 1cm was enough to change mode. The good news is once the cavity is properly tuned for a TE0,1 mode, it has a significantly higher Q because of low field strengths along the walls.

It should be possible to tune the cavity with a large movable circular plate as the short at the narrow end. Because the mode is TE0,1, the field strength around the edges are small. Having looked over the square tuners found in the lab, it is clear when field strengths are low on a certain wall, that fairly large spaces can be used (see attached picture).

A simple circular cavity at 152mm in diameter was simulated with a loop instead of a probe to properly generate a TE0,1 mode (see attached pictures). Fabrication of a loop probe maybe a difficult task considering it has to terminate in an N connector and would have to be inserted from the inside after the cavity has been built.

Here is what I will do next week:

  • Finish getting both probes matched to the cavity.
  • Fill the interior with Teflon and check the Q
  • Double the size of the large end to see if the TE0,1 at the narrow end changes to a TE0,2 mode in the large end or some other mode.
  • See if any further optimization of the cavity length can be done.