FLEXIBLE COAXIAL CABLE,

Flexible coaxial cables of the helical dielectric and corrugated outer-conductor construction were investigated for possible use as a broadband transmission line and as a substitute for limited rotary joints for the proposed 600-ft antenna of the former Naval Radio Research Station, Sugar Grove, West Virginia. The 78-in.-diam cable would have been unsuitable in broadband transmission up to 4400 Mc due to the high VSWR exceeding 3 which occurs over a narrow bandwidth of about 100 Mc centered near 3600 Mc. This high VSWR is attributed to the cables helical dielectric construction. As a substitute for a limited rotary joint the 78-in.-diam cable would have a lifetime of about 2000 bending cycles before mechanical failure of the end connectors. Fatigue fracture of the inner conductor occurred at 10,000 bending cycles. Cable of 1-58-in.-diam was found to have a bending life of nearly 1000 cycles before fatigue failure of the outer conductor. Above 1800 Mc this cable also appeared unusable because of high VSWR. The mechanical limitations and anomalous performance at microwave frequencies would prohibit the use of these sizes of cable for suitable operation in the microwave region. The anomalous effect was suspected and is believed due to the helical dielectric construction. A literature search indicates that this effect has not been analytically explained. Author