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Why are rectangular cavities preferred for standard microwave ovens with a frequency of 2.45 Ghz? What is the reason that you can hardly find a circular cavity? What are the disadvantages of cylindrical cavities? Are there any advantages?

My assumption is that the radius of a cylindrical cavity would be bigger than the largest side of a rectangular cavity so that the dominant mode can propagate. Maybe the mode propagation in cylindrical ovens is not that good to get a more uniform field distribution and therefore even heating. Are there also reasons of manufacturing? Any reference to a paper or book is very appreciated.

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Update:

yesterday i found some advantages/disadvantages in literature of circular waveguides, but i dont know if i can translate these into cavity resonators:

advantages:

  1. TE01 mode in circular waveguide has the lowest attenuation per unit length of waveguide hence suitable for distance waveguide transmission. --> since microwave ovens dont want to transfer anything over long distance i think this is negligible

  2. in circular waveguide, TM01 and TE01 modes are rotationally symmetrical and hence rotation of polarization could be overcome. --> why is this an advantage?

  3. the circular waveguides are easier to manufacture and join than rectangular waveguides.

disadvantages:

  1. propagation in rectangular waveguide is easier compared to circular waveguide.

  2. circular waveguide occupies more space compared to rectangular waveguide system.

  3. due to infinite number of modes existing in a circular waveguide, it becomes very difficult to separate these modes.

  4. angle of polarization of wave changes because of discontinuities and even small irregularities, as a result of which coupling energy out of waveguide at receiving end becomes difficult. --> is this what you mean @CuriousOne? but why is this a bad thing?

  5. Fabrication of certain type components is more difficult for circular waveguide

Maybe someone with a better understanding of microwaves can briefly explain what (dis-) advantages would be relevant for microwave oven cavities.

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    $\begingroup$ Good question. I would think that it has to do with the ability of a rectangular waveguide to keep the polarization of the wave well defined even when it is bent. $\endgroup$ – CuriousOne May 20 '16 at 22:26
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I am currenly trying to build a cylindrical MW oven here's what I foud out: you dont want TM01 and TE01 modes , that's for a waveguide. For an oven, for the sake of heat distribution you want as many nodes as the cavity can fit (=length/half wavelength)

-pros : can withstand vacuum

-cons:

*calculating the dimentions is hell. The Bessel derivative calculators are hard to find and inconvenient

*it requires a stand

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Maybe a rectangular microwave oven has the same simple advantage as rectangular furniture: rooms are usually rectangular, and any other shape of furniture would use the space less efficiently.

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