Generic EM Drive Information
This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.
Simulating With MEEP
MEEP is is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems. A number of people, including @aero, have been using it to simulate the evolution of the fields within the EM Drive.
Conservation of Energy and Momentum
See Energy Conservation and Momentum Conservation for discussions of the implications to these principles.
See calculations pertaining to the relationship between thrust and mode shape at Notsosureofit's post and Rodal's response.
An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.
The natural frequencies (and therefore the mode shapes) of a cavity are sensitive to the dimensions of the cavity.  A dielectric insert lowers the natural frequency at which a given mode shape takes place. Here is a plot of what a few mode shapes in a cylindrical cavity look like when viewed perpendicular to the circular cross section plane.