Chokes in rectangular waveguide cavity resonator

I got a tutorial for drawing a rectangular wave guide cavity resonator in HFSS.But I didnt understand the reason the two cyllinders are attached to the cavity (attached thumbnail).The tutorial calls it choke.But I didnt understand its use and is it really necessary or optional.

These cylinders alone do almost nothing (assuming waveguide is used in fundamental mode). You get some evanescent wave in the cylinder, as the diameter is too small to support waveguide propagation. So they virtually do not distort the field propagation.

They start to act when you put something in it. Think of an inner conductor/wire forming a coaxial structure. You can take or apply RF via such an entry, but also DC to bias an (active) circuit. When the length is about a quarter wave (in air), and the end is shorted for RF, the wire inserted into the waveguide will appear as a high impedance (quarter wave transformer formula) to the circuit where it is connected to.

The blocking action due to the quarter wave resonance does the "choke" function here.

what If I put another co axial cable in the wave guide like this....and also put an IRIS in between then please answer me few questions

1)how can these inductive screw and iris be used to tune the S11 reflection coefficient and minimize it.

Hello,

The iris can be seen as a combination of a vertical iris (inductive behavior) and an horizontal iris (capacitive behavior). So it behaves like an LC circuit, it may resonate at some frequency.

I can't see whether the post is connected to the wave guide or not.

Generally, metal that connects upper AND lower side together results in an inductive behavior. Metal that connects to only upper or lower side will result in capacitive behavior. As you may know from lumped circuit and/or transmission line analysis, parallel reactance can be used to match a load to a source. Parallel reactances are used in double and single stub tuners.

Thanks a lot for your help .Just one final thing the waveguide tuner that I am using to match the impedance whats the relation between the permittivity,di electric loss tangent and bulk conductivity of the tuner with the inductance it offers.

Those "chokes" are only chokes if they are long enough. If they are too short, significant amounts of power will leak out.

If you add a coaxial center conductor, all bets are off unless you weld/solder the center conductor to the outer conductor somewhere down the tube(s). And the wire will not necessarily be inductive--it will depend on exactly where you attach the center conductor to the outer conductor.

To be honest, I have no idea. I don't know what you have in your hands and field distribution is mostly too complicated to find an exact solution for what you want.

hii..
im simulating a planar magic tee.for minimum reflection at a particular frequency we can use iris.
can u tell me what will be effect if i change iris length and position of iris?
due to change in position of iris ,the reflection coefficient parameter changes(minimum of maximum) and
due to change in iris length ,the return los shifts to left or right.
is that true?