HF low-loss nanosecond variable delay line

A survey conducted by Clark and Hardell (1980) indicated that, although numerous time delay techniques have been investigated, no technique had all the characteristics desired for the HF delay line application. Many available delay lines are capable of microsecond delay variation, but are not capable of nanosecond resolution. A coaxial transmission line with a helical center conductor wound on a ferrite rod embedded in a high-permittivity dielectric material has been studied and found to have the desired characteristics. The time delay through the line is varied by applying an electrically controlled dc magnetic field to change the permeability of the ferrite rod. Attention is given to design principles, aspects of material selection, model construction, and experimental results. It was found that the use of the considered transmission line provides a viable technique for employment in the HF band. The line is capable of operating, without tuning, over the HF band and well into the VHF band.