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 TE01wave couples in such bends to the TM11and TE1nwaves. 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-TM11coupling causes only a small increase in TE01attenuation. Mode conversion to TE1nwaves 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 TE12wave at critical frequencies near 5-mm wavelength causes a TE01attenuation 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.