In designing coax to waveguide transition, by putting the coax at λ/4 distance from the short circuit end of the waveguide and by tuning the depth of coax core in the waveguide, I could not obtain more than "-3 dB" for S12 . It seems that a post on the wall of waveguide is also needed. Does anyone know any start point for designing the post?
May be I am reiterating stuff , firstly did you ensure the maximum power transfer when the stub was designed ? The post-wall : http://en.wikipedia.org/wiki/Post-wall_waveguide
has to be designed based on what you need in terms of Q factor , power at the load -end and even the phase ! hope this helps...
if you are designing the transition for a particular frequency then backshort=λg/4 at that frequency and penetration of the pin is normally half the height of the waveguide(i.e h=b/2). this is a very good starting point;it can give good VSWR ;fine optimization may be required. for broadband design a post can be added at the tip of the pin and tuning screws at the opposite wall (opposite to input) can be added.
There is book by Izadian and Izadian on microwave transmissions. They cover this topic.
I have designed the matter. Keep the short circuit distance at λg/2 . the inner coaxial conductor is allowed to penetrate upto λ/4... By default this will result in narrow s11 bandwidth. u will get very very small s11 value for a narrow range of frequency... keep a thin cylindrical disc over the coaxial conductor so that s11 bandwidth increases.. for better matching keep a cylindrical post inside the adapter...
- Badges
- Science topic
- Similar topics
- Engineering
- Telecommunications Engineering