Researches on transmission of TE01 waves in circular waveguides in the vicinity of 25 and 35 Gc/s

The characteristics of two 50 m lengths of straight circular waveguide have been measured at 25 and 35 Gc/s. The first line was made from solid copper tube of 50 mm bore by drawing to an overall tolerance, including ovality, of ±0.03 mm. The second line was composed of helical waveguides obtained by winding rectangular copper wire on a precision mandrel and surrounding it by a sheet of plastic material reinforced with glass fibre: the bore and overall tolerances were again 50 mm and ±0.03 mm. With the two lines short-circuited at both ends, measurements were made with 0.02 microsec pulses; for favourable settings of short-circuiting piston, attenuations as low as 0.3 neper/km at 35 Gc/s and 0.6 neper/km at 25 Gc/s have been measured on both lines, these results exceeding the theoretical attenuation by only 25¿40%. A third line, made of flexible helical waveguide of 50 mm bore, was bent with radius of curvature extending from 50 to 1000 m; attenuation measurements showed that the losses of the TM11 wave were 1 500 times higher than those of the TE01 wave at 35 Gc/s, and 500 times at 25 Gc/s.