helping me to design a coax to waveguide transition

I am trying with HFSS to design a circular waveguide to caxial transition in X-band but even after optimising the probe length and dia of short to waveguide wall i am not able to get the bandwidth
Can anybody help me with that

Hi,

maybe this can help?



flyhigh

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.

If all you are doing is a probe and a backshort, then do not expect to get much bandwidth. HP had a pretty good design where they used λ/4 transformers to step down the impedance to the probe, which was a centerpin of the coax connector grounded to the other side of the waveguide, with a backshort in reduced height guide.