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Waveguide discontinuity with centered circular aperture

  1. May 16, 2012 #1
    This is the first time I write in the forum. I hope to be fully in-topic.
    I'm dealing with a rectangular waveguide discontinuity: a perfect-conductor plane orthogonal to the propagation direction, with a circular aperture in the centre of the guide section. The structure is symmetrical along the x axis and the y axis and I drew it in the attachment, where the z axis is outgoing from the screen.
    In my note the professor talked about a strange "Edge Theorem" (which we didn't demonstrate and which I can't find in any book). The Theorem says that:
    - a field component which is parallel to an edge is diffracted but not folded (and so it doesn't generate any new field component);
    - a field component which is orthogonal to an edge is diffracted and folded along the plane perpendicular to the edge (so it could generate a new field component).
    The discontinuity is reached by the fundamental TE10 mode: in my coordinate system, it has EY, HX and HZ field components.
    According to the Theorem, when EY reaches the upper and the lower part of the circle (points A and D in the picture) it is orthogonal to the circle edge and it generates an EZ component.
    When HZ reaches the left and the right part of the circle (points B and C in the picture) it generates HX; similarly, in those points HX generates HZ.
    But what about HY and EX? I can't see how they are generated, but they are, because I wrote in my notes that the field becomes a 6-components field.
    The only electric field component is EY, but when it reaches the oblique edge between A and B, it generates an EZ again and not an EY! What is wrong?
    Thank you anyway!


    Attached Files:

  2. jcsd
  3. May 16, 2012 #2
    I don't have a copy of the article, but Hans Bethe wrote a paper during the War on microwave couplers using small holes. These later became referred to as Bethe holes. See http://prola.aps.org/abstract/PR/v66/i7-8/p163_1.
    I would also look in Marcuvitz's Microwave Handbook..
  4. May 17, 2012 #3
    I tried to read the article but it's not available, unfortunately. Thank you anyway for your reference! I read also the Marcuvitz's Microwave Handbook: it deals with such a discontinuity, but it considers just the equivalent circuit (an admittance) and not which field components arise from it.

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