Hello, you may be able to "tune" the device for increased bandwidth. You can do this by drilling and tapping holes into the waveguide wall and inserting screws. Once the screw is in, adjust the screw height to optimise performance, then lock the screw off with a locknut. In-line with the probe will probably work best and you may need more than one. You can also put "pucks" (dielectric or aluminium) into the waveguide aperture to tune the transition. This is a simple fix and you can play around with the diameter and location. Fix the pucks with a good qualitity adhesive, once you have found the best location (for epoxy; eccobond 286 or silicon; RT3145). I've even seen this done with steel nuts! Be careful if the device will see high power, as you might get some electrical arcing, try something like PTFE pucks if this is a concern and test at low power.