how to realize cross coupling of combline filter?

i am designing a combline bandpass filter, it is a caivty structure.
there is a positive cross coupling in this design, but it is difficult to
find a feasibly physical structure to realize it.
does anyone have any idea of this?

thanks

Yes I do, there are several ways you can acomplish this, but for a novice the simplist way is to use a wire or shim to connect across, now location is important
so experimetal methods may be needed.

The way you've drawn the circuit already suggests coupling between the end resonators. If the center conductor of the end resonators are moved closer to the top and the center conductor of the middle resonator is moved closer to the bottom, then the end resonators will 'see' each other better and thus couple to each other.

thank you guys. actually , i didn't express the problem clearly.
the pic i draw is just a part of my filter and the position of resonators has been limited. the only way i do now is to put a wire connecting the first resonator and the last. but the simulation shows there are
some wired thing happened to the S parameter so i can't calculate the coupling coefficients accurately. so i think another way to realize this cross coupling may eliminate the awkward.

the point of this case is to find a way to couple electric field from the first to the last resonator. generally a wire can do that, however, any other ways except that?

anyway, experimental tuning is always the last step.

Yes, there is but it is difficult compared to the wire, if you dont already know,
about this method then you probably will have way too much trouble

the way is in a square configuration using iris's

Added after 2 minutes:

there are some papers out there that discuss the procedure but i do not remember where off hand. you really need a good grasp of how these, comblines, work physically to understand them weel enough to become creative.