Circular electric wave transmission through serpentine bends

An otherwise straight waveguide line with equally spaced discrete supports may deform elastically into a serpentine bend under its own weight. The TE
01
wave couples in such bends to the TM
11
and TE
1n
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. TE
01
-TM
11
coupling causes only a small increase in TE
01
attenuation. Mode conversion to TE
1n
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 TE
12
wave at critical frequencies near 5-mm wavelength causes a TE
01
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.