The Attenuation of the Holmdel Helix Waveguide in the 100-125-Kmc Band

The advantages of overmoded circular waveguide using the TE 0 i mode for long-distance transmission in the millimeter-wave region have long been recognized.1 The added advantage of the circular helix waveguide in giving spurious mode suppression has also been considered. 2 The propagation characteristics of the Holmdel, N. J., Bell Laboratories two-inch diameter helix waveguide, which is made to very precise tolerances, have been investigated extensively, and its attenuation has previously been measured from 33 kmc to 90 kmc. 3 The work reported on here extends these measurements to 125 kmc. Over the previously measured band the attenuation decreases with increasing frequency and falls below 2 db/mile at 90 kmc. It was previously not known how high in frequency this decreasing trend would continue nor to how low the attenuation would fall. The measurements * This paper was presented at the Conference on Precision Electromagnetic Measurements, June 1964, Boulder, Colorado.