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.



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


  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.


  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.

  • 1
    $\begingroup$ 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
    Commented May 20, 2016 at 22:26

2 Answers 2


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.

  • $\begingroup$ ...and you can't conveniently put a flat dish in a cylindrical cavity without wasting space $\endgroup$ Commented Feb 24, 2022 at 9:14

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


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

*it requires a stand


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