Derivation of an Equation for the Cut-Off Diameter of a Frustum-Shaped Cavity at a Specific Resonant Frequency

I am scheduled to speak at the SmallSat Conference 2017 in Logan, UT this August. It is just one of the Swifties, where you get 3 minutes to talk about a subject, but they are letting me include a paper on the subject into the proceedings, which I have never done before. It is essentially a summary of the state of the investigation of the EMDrive as I know it, and what I believe are testable predictions that would differentiate between possible explanations for the phenomenon. I cannot put the paper here, but I am going to link to a paper I wrote that is referenced by it.

One of the important features of a waveguide that some of the proposed explanations rely upon is the cut-off frequency of the waveguide, or the cut-off diameter of the frequency. The problem is that, because the cavities being used are in a shape that has not been considered useful before this, the cut-off diameter doesn't have a reliable equation in order to predict it. This is my attempt at deriving one, and I hope that it proves valuable. I don't have the tools to test it in a simulation, but some people on the EMDrive thread at the NASA Spaceflight Forum gave it a quick go and it looks promising.