Abstract
An otherwise straight waveguide line with equally spaced discrete supports may deform elastically into a serpentine bend under its own weight. The TE01 wave couples in such bends to the TM11 and TE1n waves. The general solution of coupled lines with varying coupling coefficient is applied to a serpentine bend by an iterative process, and evaluated for the elastic curve resulting from a periodically supported line. TE01-TM11 coupling causes only a small increase in TE01 attenuation. Mode conversion to TE1n waves can become seriously high at certain critical frequencies when the supporting distance is a multiple of the beat wavelength. In a copper pipe of 2⅜ inch O.D. and 2 inch I.D., the mode conversion to the TE12 wave at critical frequencies near 5-mm wavelength causes a TE01 attenuation increase of 90 per cent and a spurious mode level of −7 db. These mode conversion effects can be controlled effectively by inserting mode filters.

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