Country: United States
Date: June 2008
Why in a medical linear accelerator the cross-section of a
waveguide used to transmit microwave power is rectangular in shape
whereas those of an accelerating waveguide used to accelerate the
electrons is circular?
The difference between a circular and a rectangular waveguide is
polarization. A circular waveguide will pass (or conduct) a high
frequency power of any polarization, whereas a rectangular waveguide
can only pass a signal of one specific polarization.
Not being an expert in either of the specific uses you quote, I cannot
tell you why polarization is important in one of the applications you
mention, but not important to the other.
The shape of the waveguide affects the shape of the electromagnetic field
produced. Different applications require different field shapes for best
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Update: June 2012