Capacitive Iris

Can anyone one help me with how to use capacitive iris's to match a load in a waveguide antenna? I have been unable to find equations for height and locations of the iris.

If you use 3D software, just put the iris and optimize the length width and height keeping antenna impedance on the other end.

Added after 43 seconds:

Equations may not work for broad band so go for simulation.

Ok I understand the idea of manipulating the iris in HFSS to fix any issues. But are there any equations to approximate the location and size? Maybe just some things to try and consider when placing them?

Yeah, how about a smith chart!

why keeping antenna impedance on the other end?
im simulating magic t with iris .Is the same required in T also?
(i mean to say impedance for T .)