Circular Waveguide Module

Hello everyone,

I have designed a circular waveguide module which expands at the center (like a B2B horn antenna, without radiation, its a waveguide only). Pictures are attached.

I can observe from the electric field distribution that the dominant TE₁₁ mode of circular waveguide changes to an interesting flat phase (maybe an HE₁₁ mode) when it is expanded or flared to a certain angle.

My questions regarding this are:

1. What is the theory behind this making a flat phase at expansion? Is the same theory of a corrugated circular horn antenna?
2. And, can we utilize the flat phase inside the waveguide?
3. There is a softwall which converts TE11 to HE11 mode (variable impedances). Is it possible to maintain HE11 mode from softwall till expansion as a single mode of propagation during the transition?
4. Can we utilize this waveguide module towards an application which requires a flat phase?

Will appreciate if I can get a direction of how to analyze the theory behind it and to utilize this module in some application.

Please see the pictures.

Hi musmanm,

What are you referring to by "flat phase"?

From flat phase, I mean that field at the expansion section has a constant phase. And it is also axis-symmetric.