for a project I am doing research on microwave ovens and their operation. I have researched most of the electronic components but I was wondering about one part, the magnetron tube. I have looked it up several times and I cannot find it anywhere, which way do the tubes emit microwave radiation? Is it parallel to the axis of the magnets or is it radially through the filament? Or is it in every direction?
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The most basic magnetron is a wire parallel to the magnetic field; in such a tube the electrons circle the wire, and since the emission of an accelerating electron is perpendicular to the acceleration vector, and since the acceleration vector changes as the electron makes a complete loop, I believe you would expect isotropic radiation.
More usually, a number of resonant cavities is added. This makes the magnetron a "cavity magnetron", with resonant frequency better defined - it was the breakthrough that enabled radar, and arguably was responsible for Britain winning the Battle of Britain thus preventing the German invasion early on in WW II.
In a cavity magnetron, the radiation only comes out on the output port - everywhere else it is reflected, with the resonant frequency being reinforced.
Some interesting information on the early history of the magneton (and radar): http://www.johnhearfield.com/Radar/Magnetron.htm
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