Compact Water-Based Coaxial Delay Line

The coaxial cables are commonly used as delay lines in phased arrays for steering the antenna beam in the sky. At low radio frequencies, larger array size and element spacings necessitate use of longer delay lines for phasing, resulting in networks of unmanageable dimensions. This problem could be overcome by realizing lines on high dielectric constant medium. We have developed a water based composite dielectric medium which has an effective dielectric constant of ∼ 40. A coaxial cable of about 22cm long has been constructed using it. Its insertion loss varies from 0.5 dB to 2.5 dB and reflection coefficient is better than 10 dB over 30–360 MHz band. Its delay characteristic is shown to be equal to that of a 1m long teflon-based cable, demonstrating the reduction of cable length by a factor of 4.5 through the use of a high dielectric constant composite medium. The cable parameters have been optimized and a prototype has been built to validate the design.