Discussion Forum

1. See the archived discussion already noted.
2. You can create a circular waveguide port in Comsol Multiphysics and set the port to be driven by a TM01 mode. That will immediately give you a local spatial distribution in a waveguide, with the properties you asked for. If you would like to see the mathematical expressions for a circular TM01 mode, look in any good textbook on EM. And if you want your distribution to exist/propagate outside a waveguide, you can always radiate it from your circular waveguide, with or without first flaring it into a circular horn.
3. I object to the term "radially polarized" since it is not a true form of "polarization" at all, but rather a spatial distribution of fields. In a waveguide, we call such distribution a "mode" (or a combination of modes), not a "polarization." Modes and polarizations are not the same things.
4. Some people are interested in radiating atypical spatial distributions for short range communications. Is that why you are interested in this? If so, you should look up "orbital angular momentum" (OAM) antennas and "OAM multiplexing" on the internet.

Hello Robert Koslover Thank you very much for your nice explanation. I still have dificulty come up with my expressions for input electric field. I have a cavity which is not a cylinder ( please see attached images) . I would like to create a THz source in RF Module in such a way that the electric field of the incident THz wave contanies radially orinted vectors and have a hole on the symetry axis and the wave propagates along x direction. I have already been trying it for 3 weeks and still couldn't find any solution. I use COMSOL 4.3 and this version does not contains circular port. (only rectangular port). I am intrested radiating spatial distributon not for comunication purposes. I apreciate any idea and thank you in advance for your time and considerartion Kind regards Mozhgan

I don't recall the limitations of version 4.3. You could still define a circular TM01 mode mathematically, I presume, so I would recommend that.

If not, consider this alternative work-around: Create a smoothly tapered rectangular (or square) to circular, straight transition section. Connect the circular end to drive your cavity. Drive the square end with a TM11 rectangular mode (I'm assuming the code allows you to specify that). This works, because the TM11 rectangular mode is the rectangular-analog to the circular TM01 mode, so a sufficiently smooth/gradual straight transition will yield a clean circular TM01 mode at the circular end.