Coaxial Dielectric Resonator BandPass Filter

i need some tutorial to design coaxial dielectric resonator filter. What coupling technique should be used between resonators? how to model coaxial dielectric resonators in HFSS ? i found some pictures of such filters on internet but coupling mechanism is not apparent. Picture is attached here for reference. Kindly help me out and provide me with a design procedure of such filters.

Dear Ali,
I found some papers to do that as following:
1)Basic Data on High-QCeramic Coaxial Resonators
2)IEIECE Trans. Electronic, Vol.E82_C, Bo.7, July 1999, Page 1110
3)Ceramic Bandpass Filters-Boon or Bane?
4)A BANDPASS FILTER USING DIELECTRIC COAXIAL RESONATORS WITH A TEMPERATURE-STABLE STEPPED-
IMPEDANCE STRUCTURE
5)A Direct-Coupled Lambda_4-Coaxial Resonator Bandpass Filter for Land Mobile Communications

Please let me know if you find others.
Best
Vahid

Coupling mechanism is realized by small apertures between resonators.You can imagine that being as inductively coupled parallel resonance circuits.Each inductor is magneticaly coupled to neighbour inductors..

if you pop the metal shield off that filter you have, you will likely find the coupling resonator to resonator is done with etching off the metal resonator shields near the top where one resonator touches the other.

If you are making your own small-quantity resonator filter, the standard way is to use series chip capacitors between the center conductors of each resonator. Also one often uses a shunt capacitor of small value to "pull" the center frequency of the resonator down a little to "tune" the filter shape.